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Musings of an Energy Nerd

How Much Fresh Air Does Your Home Need?

The latest version of the ASHRAE 62.2 residential ventilation standard calls for bigger fans — and Joe Lstiburek is ticked off

Max Sherman (left) and Joseph Lstiburek have been disagreeing about appropriate minimum ventilation rates for many years.

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) has had a residential ventilation standard since 2003, when ASHRAE 62.2 (“Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings”) was first approved for publication. (For more information on providing fresh air for homes, see Designing a Good Ventilation System.)

Until recently, the basic ventilation rate formula established by ASHRAE 62.2 back in 2003 — 7.5 cfm per person plus 1 cfm per 100 square feet — has remained unchanged. (The standard assumes that the number of occupants in a home equals the number of bedrooms plus one.)

However, the latest (2013) version of ASHRAE 62.2 includes a significant change in the decade-old ventilation formula. Under the new formula, high-performance homes will need to be ventilated at a higher rate, namely 7.5 cfm per person plus 3 cfm per 100 square feet. This means that for a tightly built 2,400-square-foot home with 3 bedrooms, the minimum airflow rate of the ventilation equipment has jumped 89%, from 54 cfm to 102 cfm.

This new formula has been criticized by some building scientists, especially those who have long argued that even the older formula — the one specifying a lower ventilation rate — was probably too high. The most prominent critic of the new formula is Joseph Lstiburek, a principal of the Building Science Corporation in Massachusetts and one of the original members of the ASHRAE committee that developed the 62.2 standard.

One of the most prominent defenders of the new formula is Max Sherman, a senior scientist at Lawrence Berkeley National Laboratory and the former chairperson of the ASHRAE 62.2 committee. (Sherman is also a Holladay Distinguished Fellow, an ASHRAE honorific named after my grandfather.)

Getting rid of the infiltration credit

The 2010 version (and earlier versions) of ASHRAE 62.2 asserted that the (old) formula used to determine the minimum airflow rate of ventilation equipment was based on the assumption that all…

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  1. dankolbert | | #1

    Thanks for the report, Martin. Should be exciting to watch. And survive.

  2. user-963341 | | #2

    Resistance is futile?
    I think in terms of winning hearts and minds (since this seems to be a battle) Max Sherman made a big mistake with that line.

    As to the concept of having a single ventilation standard for every new home; it is, let me find the word...stupid.

    ASHRAE does some great work but to be honest I'm seeing an awful lot of bureaucratic sh... er, stuff, from some of the committees. I have sat through enough committee meetings that I fully understand how this happens. Sometimes the process overwhelms the result. The need to produce a result trumps all.

    Not being in the room with the committee on this one I can't comment specifically, obviously, but I wonder if perhaps there may have been some clash of styles, shall we say, as well.

    For years I've been pushing the idea that getting ventilation right is as important as anything we do. Before we accept the 62.2 or, sorry Joe, one persons ideas, we should think long and hard about ventilation and what we really know about it. In most cases I think we know way too little.

  3. Expert Member
    Dana Dorsett | | #3

    Having your cake, and eating it.
    The higher rates would not have such an obscene energy use penalty if it also included a requirement for occupancy sensor control, interrupting ventilation for periods when the home is unoccupied or occupant activity is extremely low.

    Lstiburek is dead right on the (lack of ) efficacy of exhaust-only for properly distributing ventilation air compared to balanced & ducted systems. (It doesn't take rocket-science or hard math to figure that out either.)

  4. GBA Editor
    Martin Holladay | | #4

    Response to Dan Kolbert
    I think we will all survive the ventilation war. One comforting fact: no matter what types of equipment the building codes may eventually require builders to install, the operation of ventilation equipment will continue to be under the control of the homeowners. Just because your house has a big ventilation fan, doesn't mean that you have to run it for 24 hours a day.

    Even Max Sherman admits -- perhaps with a sigh of regret -- "There are no ventilation police."

  5. GBA Editor
    Martin Holladay | | #5

    Response to Bill Smith
    You are correct that the results produced by committees are often ungainly. What sticks in Joe Lstiburek's throat is the standard's high ventilation rate. What is striking to me, however, is the ungainly formula that builders are supposed to use to calculate the infiltration credit.

    Code writers and standard writers need to come up with guidelines that work in the real world -- that is, guidelines that can be implemented at the average job site. A simpler method for calculating the infiltration credit would better serve that goal.

  6. GBA Editor
    Martin Holladay | | #6

    Response to Dana Dorsett
    I think we can all agree that exhaust-only ventilation systems don't distribute fresh air as effectively as supply ventilation systems or balanced ventilation systems.

    I nevertheless maintain that any residential ventilation standard should include guidelines for the use of exhaust-only systems. In a small, open-plan house, exhaust-only systems can work well. They don't cost much to install, and they require only very small amounts of electricity to run.

    We need to promote a range of common-sense ventilation systems, and we need some common-sense (and flexible) guidelines for builders on how these systems should be installed. Hopefully, the end result of the current debates will be an improved residential ventilation standard -- or perhaps several competing standards.

  7. user-1031273 | | #7

    Correction to the Math of the 62.2-2013 Standard
    The 2013 version of the Standard does have formulas that are not easy to deal with, but those formulas were in the ASHRAE 136 Standard which was a separate Standard. One less Standard to refer to. Unfortunately the N factor calculations that you refer to are for the 2010 version of the standard and do not apply to the 2013 version and really should not be referenced in a discussion of the 2013 Standard. It is really important not to confuse the new calculations with the former ‘N’ factor. They are not the same and results will be way off the mark.

    The ventilation rates in the two versions of the standard are remarkably similar if you include the infiltration credit from the 2013 calculation, and it varies in the 2013 version (unlike the 2010 version) depending on the tightness of the building. Taking advantage of the infiltration credit calculation in the 2010 Standard required referring to two other standards.

    Boiled down, the 2013 infiltration credit is pretty simple:
    Qinf = 0.052 x Q50 x s x wsf

    Qinf is the infiltration credit or “effective annual infiltration rate”;
    Q50 is the measured CFM50 value for the building;
    S is a story factor;
    Stories 1 1.5 2 2.5 3
    S factor 1 1.18 1.32 1.44 1.55

    Wsf is the weather factor from the 1100 or so stations included in the Standard, but note that most of us only work in one or two states. The number of wsf factors varies from just two in Delaware to seventy-six in Alaska so you don’t have to remember all 1100!

    So if we take a 1500 square foot, 2 story, 2 bedroom home in Concord, NH, the ventilation rate from the formula is 38 cfm with the 2010 version and 68 with the 2013 version. If a blower door test is done with a CFM50 of 1000, the required ventilation using the 2010 standard would drop to 29 cfm and with the 2013 version would drop to 30 cfm. Note that if the infiltration credit was not applied in the 2010 version (requiring the application of two other separate standards), the rate would stay at 38 cfm which would be higher than the 2013 version.

    As you know, most new building codes require blower door testing, so it shouldn’t be that onerous to get a number.

    Appendix A alternative for existing homes was in the 2010 version of the standard, so it isn’t new. This allows existing fan products to remain in place (a significant savings for weatherization programs) with a minor adjustment of the whole building rate if fan flow rates are low or fans are missing or not ducted to the outside. And sometimes with a minor adjustment of duct runs or different controls, the existing fan can satisfy the requirements of the standard with very low to no cost.

    As for the issue of exhaust-only or supply-only or HRV/ERV ventilation, that’s a discussion that can go on forever. The fundamental question is whether mechanical ventilation is necessary at all, and I would submit that most of us in the industry think that it is. When houses get as tight as a plastic bag over the head, some mechanical ventilation is important. Removing pollutants at the source like kitchens and bathrooms is a good thing. The pollutants don’t circulate around the house that way. I’ll leave the rest of that discussion for another time.

    There are some great systems around for gently distributing fresh air around the house. But they have to be installed properly and maintained properly to work properly. The 62.2 Standard is a minimum ventilation standard. It is a system. It has a lot of parts, and they all need to work together. I’m afraid the meaning gets lost in the thunder of the rhetoric.

  8. GBA Editor
    Martin Holladay | | #8

    Response to Paul Raymer
    Thanks for correcting my confusion concerning the formula used to calculate the infiltration credit. I was consulting documents that referenced the 2010 version of the standard, and ended up using the old formula by mistake. I have corrected the article to reflect the information your provided.

    Although you are correct that "most new building codes require blower door testing," that's a very different statement from "most new homes get a blower door test." In fact, only a very small percentage of new U.S. homes are tested with a blower door, so very few builders will take advantage of the infiltration credit -- at least until blower door testing becomes far more common than it is today.

    Of course, I agree with you that most new homes require mechanical ventilation. I have been writing articles urging builders to install mechanical ventilation systems for at least the last 15 years. I also agree with you -- it should go without saying -- that it's a good idea to install exhaust fans in bathrooms and kitchens.

    Just because some people want to discuss the appropriate minimum ventilation levels for homes does not mean that anyone is questioning the need for a mechanical ventilation system.

  9. pwfuiuc | | #9

    A few corrections and clarifications
    There are a few points that are relevant to this article.

    The simple equation for calculating the infiltration credit is not actually in the standard. It was a simplification that was developed outside of ASHRAE to cut through the slog of the extensive equations that were brought over from Std. 136 and incorporated into 62.2. It was developed so that people in the field could use it. The only approximation to the slog of equations in 62.2 is that this equation uses stories in 1/2 story increments rather than using a precise height.

    Also, the story factor is not simply the number of stories. It is based on the number of stories. It is actually the number of stories raised to the 0.4 power.

    It is simply not correct to imply that the engineers on the 62.2 committee had this pushed past them by other interests. There was a single vote against the change in committee, from a trade organization rep, and no comments in public review. There were comments on other addenda so it is not as though nobody was looking. The fact is that, in January of 2012, nearly the entire committee believed that the right thing to do was to maintain the same overall ventilation rate and not allow any of it to be from infiltration that wasn't estimated. There were some that wanted lower rates and some that wanted higher rates. Almost all didn't want a default infiltration rate. So what happens? You get rid of the thing nobody wants and leave the overall rate alone for now.

    The debate on distribution continues. We had that debate in committee for years. Again, it is not a question of whether the engineers got pushed aside. It is that the analyses clearly showed that whether distribution was desired depended on what the assumptions were for where the contaminants were. With one set Joe was right. With another set Max was right. And we just don't know the right answer for where the majority of contaminants are. So, without a compelling argument that most homes are better off one way or another there was not a sufficiently strong majority to go one way or the other.

    The fact is that the rate in 62.2 will be wrong for almost every house. This is the nature of a prescriptive requirement. How many houses have exactly the right flue design to exhaust combustion contaminants without any waste? How many houses have exactly the right amount of attic or crawl space ventilation without any waste? There is nothing new to the problem of a "one-size-fits-all" approach. Codes are rife with it. People just aren't used to it with whole-house ventilation. What we do have is a value that a sufficiently large number of people believe is a reasonable number to protect the majority of people from the more serious problems most of the time. Should it be lower? Maybe, but we don't know. Should it be higher? Maybe, but we don't know. There are efforts going on in that arena, but it is a very difficult and expensive question to answer. And we should not pretend that moisture is a surrogate for everything else that we ventilate for.

    I have little sympathy for the argument that people don't do blower door tests. It is a 15-minute test that should be a part of any standard commissioning process, especially if you want to claim that the house is high performance. We have thousands of retrofit auditors across the country who do not seem to have any trouble doing these tests on a regular basis. What do they know that high performance builders don't?

  10. GBA Editor
    Martin Holladay | | #10

    Response to Paul Francisco
    Thanks for your valuable comments. It's good to hear another perspective from an ASHRAE 62.2 committee member. I have edited my article to reflect the information you provided, and I have quoted you to balance Joe Lstiburek's assertions.

    Thanks for explaining the calculation behind the story factor (number of stories raised to the 0.4 power).

    You wrote, "I have little sympathy for the argument that people don't do blower door tests." The statement that the vast majority of new U.S. homes are not tested with a blower door is not an argument; it is a fact. The situation may distress you -- it certainly distresses me -- but calling it an "argument" is a red herring.

    There may be some people fighting against recommendations in favor of blower door testing, but you won't find such people at Green Building Advisor. I've been advising builders to use blower doors for years.

    But there is a strange irony to the infiltration credit offered by ASHRAE 62.2. It is only available for leaky homes; tight homes can't take advantage of it. In the U.S. today, it's safe to say that almost all builders who use blower doors are building tight homes. Since you need to have the results of a blower door test to take advantage of the infiltration credit, I feel justified in predicting that very few builders will ever use it.

  11. user-1050854 | | #11

    Ventilation Police
    Max is right! We do not have ventilation police! What we need is Blower Door Police. Every home should have a blower door test and the results posted. The BD police should enforce that and the presence of a MV system capable of meeting 62.2.

    The important times for my MV system are spring and fall in my Mixed Humid Climate. The air exchange allows comfort without the Love of My Life turning on the AC because the air in the house is: take your pick MUSTY, STALE, HEAVY, etc.

  12. GBA Editor
    Martin Holladay | | #12

    Response to John Nicholas
    I believe that building codes should require every new home to be tested with a blower door, and that building codes should be enforced.

    If the officials who enforce this requirement become known informally as the Blower Door Police -- then I am all in favor of the Blower Door Police.

  13. pwfuiuc | | #13

    Response to Martin re: arguments

    I understand that GBA has been advising the use of blower doors for years. My comment about the "argument" is that people "argue" about the rates in 62.2, and now the loss of the default infiltration credit which reduced how much had to be provided by mechanical ventilation, with the fact that most builders don't do blower door tests. My language may have been careless, but my point is that I think this is backwards. Rather than saying because people don't do blower door tests they also shouldn't have to deal with 62.2, they should say that 62.2 is yet another reason for people to start doing blower door tests.

    Tight homes also get an infiltration credit the same as everyone else. The difference is that now, instead of getting a default, you get it based on what is actually measured. If you measure less than the old default then your rate will increase relative to the old version. Up through the 2010 edition only existing homes could get a credit beyond the default, but in the 2013 edition it has been opened to everyone. Do a blower door test, get a credit.

  14. Erik North | | #14

    A few thoughts not related to the debate
    First, this statement ought to be two unrelated sentences:
    "The latest version of the ASHRAE 62.2 residential ventilation standard calls for bigger fans. And Joe Lstiburek is ticked off."

    62.2 now calls for bigger fans and in unrelated news, Joe L. is ticked off.

    Also, isn't "making some reasonable technical judgments" just a euphemism for wild-ass guesses?

    (*Edit* My wife just said, "No, Erik..."Reasonable technical judgements" are wild ass guesses with a college education")

  15. kim_shanahan | | #15

    What is a "very small percentage"?

    You say a "very small percentage" of new homes get tested with blower doors, yet RESNET claims nearly one third of new homes built in the past year got HERS ratings, which requires a blower door test for a confirmed rating. While still far from a majority, I would say one third is not a "very small percentage".

    Could it be that market forces, not spottily adopted codes, could be the game changer? Now that Senators Bennet and Isaakson have crafted a SAVE Act compromise acceptable to NAHB and NAR, which, if passed, would be a huge boon for HERS rated homes, it would appear a HERS rated house may be more common than a home adhering to IECC 2012.

    When homes routinely achieve a HERS 70 or lower, and do so on with envelope specifications and tight construction, then the new 62.2 standard may be appropriate. Here in Santa Fe, with a city code requirement of HERS 70 or better in place since 2009, we added a 62.2 code requirement in 2012 because market forces were pushing builders to ever-tighter construction - low ACH50 numbers are bragging rights at our builder lunches. Recent humidity levels have been in single digits. Not even sure we can buy a dehumidifier in our market.

    Wonder if Uncle Joe would be OK with the new standard in our market?

  16. Tedkidd | | #16

    Infiltration credits chafe my butt.
    So a crappier enclosure requires less money spent on mechanical ventilation? About as logical as giving credit for "operable windows."

    Where is Max Sherman getting his bread buttered? Is there possibility there is some incentive for this odd thinking? Could it be that higher ventilation rates will increase iaq related lawsuits, and thus the market for expert witnesses? (Anybody who claims they aren't susceptible to self-interest bias should not be trusted, they can't even tell themselves the truth).

    Leakage is not a proxy for air quality, particularly when considering seasonality. Mechanical ventilation doesn't engender high confidence either. We need to abandon wild ass guessing about iaq. We need to continuously measure and manage accordingly.

  17. watercop | | #17

    I think I'm with Ted on this
    I have no problem with prescriptive standards that err on the side of health and life safety. That said, every prescriptive standard, in recognition of the limitations implicit in "one size fits all" brute force methods, should be accompanied by a "smart", that is data-driven alternative. There needs to be an option to actively control ventilation rates on the basis of a measured variable such as CO2.

    "One size fits all" generally translates to "One size fits no one", to wit - a 3000 SF 4/3 home normally occupied by just two people, such as grandparents who occasionally host children and grandchildren, will, most of the time, need substantially less ventilation than any reasonable prescriptive standard would call for.

    On the other hand, a 1200 SF 3/2 rental property in an economically depressed area with 2 adults in the master bedroom and 2 or even 3 kids in each of the secondary bedrooms PLUS an unemployed boomerang college student or recent grad bunking on the living room couch is likely to often encounter indoor air that can be cut with a knife and need 3x the 62.2 ventilation rate to maintain reasonable IAQ.

  18. Joe Lstiburek | | #18

    Leap of faith
    It is amazing that people actually believe that you can convert a blower door test result into an air change rate for ventilation purposes. The leap of faith required to do this is almost beyond comprehension.

    Blower door tests are good at providing reasonable estimates of average annual energy use if stupid stuff is not happening in a building. To use them to verify air change rates to assure acceptable indoor air quality is beyond stupid. Infiltration is not reliable. ASHRAE Fundamentals points this out.

    Folks just seem to love the pseudo science associated with a fan and a manometer and a bunch of hand waving. Fact is that you don't know where the holes are with a blower door test. You don't know the pressures across those holes. You don't know the nature of the holes.

    To make the whole house of cards work you have to believe in an equally stupid concept which is average annual exposure as an acceptable metric for acceptable indoor air quality. And to add insult to injury the cost of the test is more expensive than installing a fan with distribution.

    What we are now getting are excessive negative pressures and part-load humidity problems in new houses. Congratulations. None of the folks on the committee seem to have any experience with new houses and multifamily construction and certainly not in the South where it is hot and humid. And when I and others point these things out they are in denial because of the vested interests they represent.

    You cannot build a tight house and suck on it with an exhaust fan and not get into trouble. You cannot ventilate at the rates specified by ASHRAE Standard 62.2 and not get a part-load humidity problem in most new houses in the Untied States. And there is no justification for the rates specified in 62.2 in diluting contaminants of concern. Only source control is effective.

    Remember this moment. What is going on now is that folks are installing fans and not running them. Or running them at a fraction of the rate specified in 62.2. In many multifamily projects the fans that are installed and not run are called the ASHRAE "tax" or even worse (or better depending on your sense of humor) the LEED "tax". You install a large exhaust fan to meet the "requirement" and then install a second system that actually works.

    Just for the record, I am not mad or angry about all of this. But I must admit I am somewhat disappointed, often bemused but not surprised. We fix a lot of these projects with supplemental dehumidification and interlocked make-up air systems. I get to be a mechanical engineer again after all of these years. It is financially very rewarding.

    Who knew that it would come to this? The good news is that at least we are not talking about vapor barriers anymore.

  19. GBA Editor
    Martin Holladay | | #19

    Response to Kim Shanahan
    You wrote, "You say a 'very small percentage' of new homes get tested with blower doors, yet RESNET claims nearly one third of new homes built in the past year got HERS ratings, which requires a blower door test for a confirmed rating."

    I'll admit that the "nearly one third" statistic surprises me. Perhaps the world is changing faster than I think.

    But I also wonder if the RESNET statistic accurately captures all new home construction -- including new home construction in rural areas where building permits aren't required.

    In the Vermont town where I live, no building permits are required. There aren't many ways that statisticians will ever know how many homes are built annually in towns like this.

  20. Joe Lstiburek | | #20

    Response to Kim Shanahan
    You live in paradise and on that basis alone the rest of us should just ignore you because we are envious. Having said that I can only wonder where you get make up air for a 400 cfm kitchen range hood exhaust or that 200 cfm clothes drier or that fireplace? You could just insert a video screen in the fireplace opening and dial in a continuous running loop of a wood burning fire to display. You could hang your clothes outside on a clothesline. And you could learn to cook outside. Perhaps grow your own food too. Hunting might be an option. Don't own a car or if you do don't park it in an attached garage. Better still don't have a garage or don't attach the garage to the house.

    Once you get to building tight you are screwed. I think you should build tight - but now you have to provide interlocked make-up air for all the air consuming appliances.

  21. HomeBuilder1975 | | #21

    Here in Houston we are now required to do door blower and duct blaster testing. And by the way, because of heat, humidity, blood sucking mosquitoes, and pollution, no one here opens their windows. And now many of us are using spray foam insulation and 1500 CFM kitchen vent hoods, so ventilation becomes imperative. Someone mentioned dehumidifiers, my HVAC contractor is now insisting we at least prep for them, and in many cases go ahead and install. Tough climate.

  22. Sal_123 | | #22

    Unintended ASHRAE 62.2 consequence?
    "You cannot build a tight house and suck on it with an exhaust fan and not get into trouble." This is worrisome, as I am considering an ICF home, ideally with a low ach50 and a wood burning stove as the primary heat source. An "optional" ERV with an air exchange system and maybe a stove designated intake air source was anticipated. But wouldn't it behoove me to "allow" a good amount of secondary infiltration at the time of the blower door test to take advantage of the infiltration credit in the calculations to downsize my mandated system, lest be at the mercy of the ruthless blower door police once I proudly display my ach50 like a badge of honor only to have it kick me in the butt? I might post-blower test go back and spray foam closed those cracks against the windows in the living room.... Thus incentivizing manipulation of the data to my desired outcome goals? Unintended consequence of ASHRAE 62.2?

  23. GBA Editor
    Martin Holladay | | #23

    Reply to Sal Lombardo
    You raise four questions:

    (1) Is it a good idea to heat a very tight house with a wood stove?

    (2) If you choose to heat your home with a woodstove, is an exhaust-only ventilation system a good choice, or would a supply-only or balanced ventilation system make more sense?

    (3) Does it make sense to make your thermal envelope deliberately leaky?

    (4) Does it make sense to try to fool the Blower Door Police?

    Concerning question (1), opinions vary. My own opinion is that you can probably do it, but you may have to crack a window occasionally to prevent the wood stove from backdrafting. For more information on this question, see these two articles:

    How to Provide Makeup Air for a Wood Stove

    A Superinsulated House in Rural Minnesota

    Concerning question (2), I think the answer is "Probably not." I think that a suppy-only or balanced ventilation system makes more sense if you plan to heat with a wood stove.

    Concerning question (3), the answer is no.

    Concerning question (4), I believe that the answer is also no. If you live somewhere where local regulations require you to comply with ASHRAE 62.2, I suggest that you comply with ASHRAE 62.2. Once your house is built, you can program your ventilation equipment to operate any way you want -- either to operate 24 hours a day, or to operate for fewer hours per day.

  24. pwfuiuc | | #24

    Exhaust vs. other fans
    One misconception I find over and over again is this concept that 62.2 is causing all kinds of problems because of exhaust fans. Quick quiz: what is the minimum number of exhaust-only whole-building ventilation systems required by 62.2? Answer: 0. Yes, there are requirements for exhaust for local source control in kitchens and bathrooms. But of course these values were not touched by the 2013 edition, so there is no increase in the amount of exhaust required (remember the original focus of this discussion). In a retrofit context, where you can increase your whole-building fan to address shortcomings in local exhaust, you can avoid having any exhaust fans at all if that is what you want.

    There is no guarantee that everyone will do the smart thing (and we have plenty of evidence to the contrary), but if you have a scenario for which exhaust-only is a bad idea - such as Joe's example of very tight construction in humid climates - don't do exhaust-only. Std. 62.2 says what the rate needs to be, not how to meet that requirement.

  25. Joe Lstiburek | | #25

    Response to Paul Francisco
    Ah, Paul, ducking responsibility, are we? Not our fault, eh? We don't tell you how to do things? How convenient.

    So supply ventilation and balanced ventilation systems are the only systems that work in a code-compliant house? Exactly my point. Note that this reality is due to the excessively high ventilation rates in 62.2.

    Folks don't get this yet and when they do they will not be amused. And then you still have the part-load humidity problem. Not our fault either, eh? It is the fault of all that energy efficiency, eh?

    We got into this mess when we tried to make 62.2 work for existing buildings, particularly low-income weatherization program homes, as well as new homes. You and Mr. Karg wanted to make sure that these homes would not be penalized.

    We should have split the 62.2 into two: one for new code-compliant houses and one for existing homes. That still might be the best option.

  26. Joe Lstiburek | | #26

    What it will take to fix ASHRAE 62.2
    To fix 62.2 requires the following:

    1. Revisiting the basis for the ventilation rates. I doubt anyone remembers where they came from and what technical justification exists for them.

    2. Addressing the differences in effectiveness of ventilation approaches. Exhaust is not the same as balanced or supply and certainly not the same where distribution or mixing is involved.

    3. Addressing make-up air when air consuming appliances are operating.

    4. Dealing with new code-compliant houses differently than existing houses.

    5. Changing the compartmentalization requirement in multi-family units to a more realistic number.

    Good luck. And I mean that in a good way.

  27. GBA Editor
    Allison A. Bailes III, PhD | | #27

    HERS-ratings and blower doors
    To shed a little light on Kim Shanahan's stating that RESNET claims a third of all new home get a HERS rating and thus a blower door test, consider these two facts: (1) The large production builders use the sampling process so they could be testing as few as 1 out of each 7 homes. (2) The HERS Standards allow confirmed ratings to use a default infiltration rate. That is, no blower door test.

    I don't know how accurate is the claim of a third of all new homes getting HERS ratings, but even if it is close to the actual number of rated homes, the number that get blower door tests is significantly lower, probably fewer than half of all rated homes.

  28. heidner | | #28

    The consequences of the change will be for more than new homes and simple remodels...

    ASHRAE 62.2-2010 and in the future 2013 is referenced by many of the weatherization programs by local, state and federal governments -- and for LOW INCOME homes. If the low income weatherization was just on Manhattan Island, or in Burbank California -- that might not be an issue, but they are also in Alaska, Minnesota, North Dakota, Montana, Maine, Vermont, etc. True -- increasing the ventilation in of the home in Alaska will help clear the air of all the VOC's brought into the house from the snowmobiles... but the increased ventilation is likely to burn up a whole lot more fuel oil in locations that must ship it in by air plane.

    Quoting from the Weatherization and Assistance Program website...

    " 16. Now that the Standard is required by my program, I am afraid I will have to install ventilation in every dwelling we weatherize. Is this true?

    Chances are you will have to install local ventilation and whole-building ventilation in most of the dwellings you weatherize, but not all.
    Once a full ASHRAE 62.2 update is published, states should start planning for implementation by seeking necessary training and technical assistance to perform the new Standard....

    No more than one full program year can pass without moving to a new Standard. Grantees can voluntarily elect to adopt the most recent version of ASHRAE 62.2 as soon as they are prepared to implement the Standard." back in 2012,

    Since it appears the intent of the changes of 62.2-2013 is to IMPROVE air quality AND we are now in the 21st century... why not emphasize demand controlled ventilation (DCV) instead of a CFM calculation? My fear is that the AHJ will be rigid and within a couple of years they will ONLY accept the calculations from the standard -- without regard to the building air quality.

    But then, I am dreaming - after all the forward from 62.2-2013 does remind the readers that the standard does not address pollutants from space heaters, episodic occupant events, painting, cleaning, and high polluting source (I read as lutefisk, under arm deodorants, crayons, sharpies, room refreshers and those wonderful scented candles...)

  29. user-1135248 | | #29

    how 'bout a more adaptive standard
    As others have said, the standards-body committees seem to be
    desperately trying to arrive at a one-number-fits-all solution.
    That's clearly impossible.

    My meager one year's worth of experience so far with an HRV
    shows me that seasonal scenarios are going to be radically
    different any way you tackle it. I've got a CO2 meter and the
    ability to monitor indoor and outdoor temp and humidity, and
    while so far I can manually set things up most appropriately
    for those conditions any given day, I could conceptually be
    replaced by a computer and a few sensors that would operate
    based on an intelligent, adaptible standard.

    For example, an 0.1 ACH average was just fine over winter for
    a single occupant with minimal interior humidity generation.
    Shutting down the ventilation entirely would let CO2 levels
    slowly creep up toward 1500 PPM or so, but it took a long time
    for the air to start feeling anything like "stuffy". But on
    some of the coldest nights a ventilation shutdown might be
    completely appropriate -- to stop on the order of an extra 500
    btu/hr heat loss in the exchanged air through a ~ 70% efficient
    core. None of us are going to die of CO2 or VOC or radon
    poisoning in a few short times of hunkering down in our cozy
    airtight envelopes over the most frigid nights.

    Or right about now in the northeast, we're looking at a hot
    and humid 4th and beyond. I've got plenty of operable windows
    but like the folks in Houston, I dare not operate them right now.
    The only air exchange I'll allow is when the cooling system is
    actively *running*, to immediately condition that incoming icky
    stuff before sending it around the house. That's why a little
    integration between the A/C and HRV was necessary. Doing
    it any other way is begging for a mold farm. Since the DER the
    place doesn't heat up very fast so the times when I'm able to cool
    and thus get ventilation are once again relatively minimal.
    That's okay, and far better than the alternative. The nice comfy
    55% or so continued indoor humidity is well worth it, which I can
    confirm by simply sticking my head out the door once in a while.

    Why does the code-required ventilation dwell so heavily on
    exhaust, which only winds up depressurizing the building and in
    humid environments allows uncontrolled moisture to seep in? How
    about a *supply*-only standard for such climates, building positive
    pressure across the envelope and then if you need spot ventilation
    in a tight house, simply open a local path to the outside? That
    would fix the whole backdraft issue [short of sealed-combustion
    upgrades] and give a much better opportunity to add conditioning to
    the incoming air path if desired. But as mentioned in a comment to
    another thread, this whole HRV balancing thing seems to be a bit
    of a shuck as it doesn't seem to make much difference.

    So the standards folks need to broaden their accomodation of
    these wildly varying situations and start writing 62.2b or whatever
    will take such things into account. Systems have gotten smart and
    automated enough that there's no reason codes for ventilation can't
    be brought up to a much more flexible reality nowadays.


  30. user-910852 | | #30

    Homeowners don't care
    Thanks for running this article featuring Joe & Max. Lots of us have opinions on that one.

    The best part of the whole ventilation / air-quality discussion is that there's hardly a homeowner that cares. Go ask them. I do all the time. Don't know, don't care.

    I'm afraid as the entire 'energy related' industry moves forward, we'll all get beat up. No public input in any of these technical discussions.

    God Bless America. (Bring on Kate Smith and let 'er sing.)

  31. BCWetcoast | | #31

    I would side with Max
    Like the article, and it would be neat to be in a large room with Max and Joe putting on a show.

    I must admit I would side with Max. I look at it this way: you are trying to tighten up houses and stop them from having any uncontrolled air movements. This is both good and bad. Saves or makes energy usage more controllable. It also means you lose the ability to control what else is in the sealed-up structure.

    So at this point you have a decision: if you want to control energy demand with air sealing, then you need to condition the air you have trapped in the home. By "condition" I mean scrub out or replace unwanted components as they start to build up and replace any components you consume while living in the sealed structure.

    How to do this? Dehumidify and filter as well as replace used oxygen and/or dilute with makeup air and possibly try to recover some of the energy used to heat or cool the air you expel air you dilute. This is where the engineer comes in and has to decide which way to go.

    If you want a sealed house you have no choice, you must condition the air inside the house, or die. The industry I come from has done this for years -- in the mines you control the air coming in by volume to replace air used by machines, people and explosives. If the mix is wrong the health and safety people get upset with too many funerals; too much air and you waste money (especially if you have to heat or cool the air ).

    So to Joe: you want to seal up houses, then do so. Just remember you still have to pay the piper to get a living environment inside the home. Yes, this will cost money, so you better do a good analysis on how much money you are going to save and come to a workable balance.

  32. heidner | | #32

    Home owners do care about both IAQ and energy
    I disagree with both Joe and Charlie. I do not believe that we can make blanket statements that home owners don't care about air quality - some certainly do and they may be fanatical about it. Like wise there are individuals that are the extreme energy misers.

    Charlie had stated, "If you want a sealed house you have no choice, you must condition the air inside the house, or die." This is of course true - at issue is how much conditioning? Individuals that use BPAP or CPAP's are often amazed that the size of the hole in the mask that you exhale through is about the diameter of a #2 wood pencil. (Of course sleeping doesn't require the same air flow as jogging...)

    While the ASHRAE standard 62.1 for commercial buildings does allow alternative measures for air quality, the residential 62.2 standard does not. As it is becoming more widely accepted and REQUIRED, the rigid enforcement of the CFM calculations is going to be increasingly painful with little real gain. The minimum ventilation rate is defined in 4.1.1. For my house - it would require the equivalent of a kitchen vent van running 24 hours a day to meet the standard -- EVEN if I live in the house only on Sundays. (876 hours occupancy). That means that the house would be fully vented while vacant 90% of the year.

    The forward, scope and overview for the standard does indeed mention air quality -- and Indoor Air Quality does have second billing on the cover page of the standard, but outside of these specific areas "IAQ" is only mentioned two or three times. ASHRAE 62.2-2013 is not a standard whose purpose is air quality - it is essentially only a ventilation standard -- that ignores the energy impact.

    An addendum to 62.2-2013 could be added that allows for an alternate path to compliance; provide guidance on IAQ based on VOC or CO2 measurements and the allowed ranges for daytime/nighttime use. Bring the standard into the 21st century and in line with the energy efficiency standards for the building envelop.

  33. Joe Lstiburek | | #33

    Response to Charlie Gould
    Let me clarify my position and Dr. Sherman's. Dr. Sherman believes that infiltration is an effective means of ventilation. I do not. Do you?

    Dr. Sherman has opposed any recognition of the positive benefits of balanced ventilation systems with distribution as opposed to exhaust-only ventilation without distribution in Standard 62.2. I believe that balanced systems with distribution are 2 to 3 times more effective than exhaust only systems without distribution. Do you?

    I believe that it is better to bring outside air into a building from a known location and then treating it before distributing it. Do you?

    I believe that excessive negative pressures are a problem. Do you?

    And here is the key point missed by most folks: there is no correlation between most contaminants of concern and ventilation rates below 0.5 ach. I believe that source control is the best approach. Do you?

    I believe that tight houses are better than leaky houses and should be ventilated with balanced ventilation systems. Do you?

    The question is the rate and an effective means to obtain it. Tell me what rate should be used for this workable balance you cite? What is the research that you base this rate on? Note that residentially the only work that I could find related to contaminants and ventilation rates was Scandinavian work dealing with mold in poorly built houses. In fact Martin Holladay did a nice piece on this earlier.

    If you have a poorly built house in a cold climate, high ventilation rates work well to address mold problems. Comfort sucks and so does your energy bill. A better approach is to construct a better house with warm surfaces and dry foundations and not ventilate as much to control mold, because you do not need to. In an air-conditioning-dominated climate, high ventilation rates lead to mold problems and do not solve them.

  34. GBA Editor
    Allison A. Bailes III, PhD | | #34

    Great beer can analogy!
    Thanks for the wonderful beer can analogy, William Geary! I'm old enough to remember those cans but young enough that I wasn't drinking alcoholic beverages from them.

  35. heidner | | #35

    The energy impact. -- RetroFit & Weatherization
    If retrofitting/weatherizing, remodeling an exsiting house, and the calculation comes in at 120CFM air ventilation... Using an average HRV, the cost to run the HRV continuously with perhaps intermittent circulation of the existing furnace fan -- can easily consume 200W. That's 200W X24hr X 365 or about 1752kWhr/year (No attempt made to estimate actual heat recovery)... just rough estimate for electrical costs.

    If the house is only occupied on weekends, that would be about 1200kWhr/year to ventilate an empty house. It doesn't matter if the air flow is balance a not, you are still moving a lot of air in an empty house. But it would meet the requirements of the standard.

    Move north to Alaska in a smaller house, sealed tight, weatherized, and an HRV added -- but moving perhaps 60CFM for ventilation. That might still require nearly 450kWhr for the HRV... but remember the fuel to run the local village generator is shipped north from Seattle during the summer time and they may not have the opportunity to send in more fuel for months. And yes the scenario is real -- January 2012.

    Because of the energy penalties for the ventilation -- even exhaust fans - the solution is simply turn them off. That defeats the whole purpose of the standard - and it also demonstrates that it fails to cover many of the real life applications.

    ASHRAE 62.2-2013 will work well in California and many of the mild climate states, but then wouldn't it be just easier to open the windows?

    Over the last several years - I have been looking at replacing my house HVAC, I've been carefully following the various manufacturers for HRV, ERV, Heat Pumps, Furnaces, etc... early on it was actually easier to find thermostats and sensing units that would control ventilation based on IAQ. However the sensing devices for homes have been harder and harder to find.. fewer manufacturers offering them. And now the reason is becoming more apparent -- with a formula only 62.2 rule - there is very little incentive to spend the money for research and development of residential products that might not be installed because -- the upcoming codes do not recognize or allow them. The ASHRAE 62.2 standard is in effect hindering innovation and by inference you might be able to argue that it could be hurting the long term energy efficiency and IAQ for many homes.

  36. Billy | | #36

    Joe Makes Sense
    Joe, you are the one who makes sense in this debate. It is apparent that Dr. Sherman is not concerned with the technical, engineering, and practical "this is how the world really works" aspects of his proposal. Apparently his main concern is the politics.

    But unfortunately politics may be the way the world works, more-so every day.

    Maybe Dr. Sherman needs to go back to the old days of drinking beer from cans that required punching triangular holes in beer can tops, before the age of flip tops. I wonder if he punched one hole and sucked his beer out of the can (relying on infiltration) or punched two holes and poured it out of the can? Or maybe he doesn't drink beer so he is unaware of the problem... That might explain things.

    Joe, keep up your good work and publications. I read them every chance I get. And keep fighting the good fight.

    And Martin, thank you for your balanced discussion of the viewpoints and debate.


  37. Billy | | #37

    Couldn't Resist

    I couldn't resist... if I could have included a pizza analogy as well it would have hit all of Joe's important food groups.

    More seriously, I have enjoyed reading the comments in this discussion here, and I do enjoy reading the studies and commentary from Joe and his colleagues over at I've been both an engineer and a carpenter and many times I've had the proverbial light bulb turn on when reading his articles.

    Allison -- I see you grew up in LA and used to live in Florida - me too, grew up in New Orleans and lived near Melbourne. I used to live in Atlanta too, working for Georgia Tech but now I live up near DC. I'll follow your blog.


  38. user-910182 | | #38

    One size does not fit all
    There have been very good discussions all the right direction we should be going. To sum up:

    1) 62.2 is a like a round peg to be placed in a variety of shaped openings based on climate and occupancy characteristics and leakage rate of the building.

    2) Intelligent controls should not only be allowed but promoted. I think that controlling ventilation based on CO2, VOC and RH is best of all worlds by giving the degree of ventilation needed when it is needed instead of one size fits all as in 62.2

    3) Agree exhaust only systems are not good for warm and humid climates. In dry and non air conditioned situations, exhaust only systems are applicable barring backdrafting problems. They are the least expensive, are already understood by most builders and provide fresh air throughout the building by drawing in air thru the envelope. It also helps dry out the envelope during heating conditions

    4) Not only are there few 'blower door police' but there are few 62.2 police that I am aware of so we can probably follow Joe's advice and ignor 62.2

  39. Jim_Maletta | | #39

    Getting away from one size fits all approach
    Thanks to all for the lively discussion on this subject. I would assume from the thread of the discussion that most of you are more involved with new construction that with retrofit on existing homes. I, by comparison, work predominantly with existing homes--and mostly outside of low income programs. I have been fortunate enough to have the benefit of working with some highly competent insulation contractors who do such a thorough job of air sealing and insulating that we frequently see turn of the century houses coming in with final air leakage rates between 3 ACH/50 and 6 ACH/50. Because of this, I strongly insist that my clients include what I describe as "supplemental" ventilation in the form of a continuous duty rated exhaust fan in one of the bathrooms. While I can understand the reservations of some of you for using "exhaust only" in a hot humid climate, Milwaukee cannot be described as either hot or humid for most of the year so the "exhaust only" proves to be quite effective. IAQ is on the radar here, but the primary worry is condensation in cold weather. The combination of air sealing with the exhaust strategy has worked well. I have been doing this for about 15 years and I have tested a little more than 5000 houses in that time. The only call-backs I have ever had are from the occasional absent minded clients who forget to turn on the ventilation fan in the Fall when they close up the house.

    I'm no engineer. I'm a pragmatic individual who looks at things with one simple question in mind: Will what I am recommending for my clients solve their problem(s) or not. I find that for the majority of my clients the 62.2 (2010) standard works quite well. I have found that in some situations where there is a large home with only 1 or 2 people in residence that 62.2 (2010) actually provided more ventilation than was really needed and it would make the house too dry during the winter. At this point, I will be very reluctant to recommend the 2013 standards to my clients until such time as I can see how it works on the ground.

    Some folks argue against the exhaust only ventilation on the basis that you are not able to control where the air comes from of how it is treated (or not) when it comes into the house. What I would point out is that in an existing home that is already the case, so we are only making effective use of an existing "resource" to address occupant needs in an economical fashion. From the point-of-view of the guy in the field, it is hard enough to talk people into using a continuous duty fan that will cost them $600 to install (material, labor and permit). Try talking them into spending $1800-2000 for an HRV to be retro-fitted in an old house. In many of these projects the supplemental ventilation needed is in the range of 20-60 CFM continuous 24/7. I don't know of any HRV that provided so little ventilation. If I put in an HRV running at 200 CFM when I need 22 CFM then i have effectively shot the rabbit with an elephant gun. Not only does it cost more to install; it also costs a lot more to operate --there is an energy penalty from excessive ventilation and an additional cost. That is something I am trying to eliminate for my clients, not add to it.

    All the engineer types in the discussion group can debate the pros and cons and the assumptions and calculations. God bless you for it because we certainly need to make this as precise as we can. From my perspective, I simply as "Does it give my clients what they need without creating any new problems?" From my boots on the ground perspective the 2010 version of 62.2 worked fine for my clients. I think we need to have a 62.2 standard for existing homes and a standard for new construction.

    On a side note, one of the folks in the discussion expressed an interest in using a wood stove in a new house as the primary heat. You can do that but you need the right equipment. For combustion appliances I always tell by clients to remember the BYOA rule-- BRING YOUR OWN AIR. If it is going to burn any fuel in your house then it needs to be equipment designed with an air in-take from the exterior so it brings in its own air for combustion.

  40. user-1135248 | | #40

    If it helps, my Fantech can
    If it helps, my Fantech can do an average of 20 - 25 CFM when it's
    set to run 15 minutes per hour on low fan. That's about all the
    ventilation I really needed over the winter [15000 cu ft volume,
    single occupant with low moisture production, CO2 was average
    700 - 800 ppm]. But I needed to buy the fancy "EDF5" controller
    for it to obtain that, otherwise the lowest possible would have
    been about 75 cfm continuous run.

    Summer is being a mixed bag so far; I'll let 'er rip when the
    HVAC system is actively cooling, but religiously avoid bringing
    in untreated humid outdoor air when it's not.


  41. BeamTeam | | #41

    Does ASHRAE want us to build leaky homes?
    A lot of great dialogue here, but I find myself in a conundrum...

    I work for a company that builds exceptionally tight homes, we perform what we refer to as "leakage" blower door tests to all of our building shells. The initial purpose is to inspect the building shell for leaks when it is still in a state that they can be easily fixed, our homes typically test between 0.5 and 1 ACH50. We then use the calculations prescribed by ASHRAE to size the whole house ventilation system.

    What I have found in my energy modeling is that the heat loss through ventilation is consistently one of the top components responsible for heat loss, even with an ERV or HRV, and close to the top when you add separate bath and kitchen fans. This makes it difficult to sell energy efficient homes if you have a client who is clever enough to come to the conclusion that a leakier home could cost less money and use close to the same amount of energy if it did not require whole house mechanical ventilation. My defense to that is always “where would you prefer your fresh air to come from, a filter or a dirty crack in the wall?” But that argument does not work for them all.

    I believe the word bureaucracy was dropped a few times on this page and I have to say that I find it very disheartening when organizations that are supposed to regulate and improve the building industry are used instead to promote procedures that will in turn make buildings less efficient. ASHRAE should be more focused on developing an organization of HVAC contractors that actually know and understand balanced ventilation and how to properly integrate these systems with different types of homes, instead of making it yet more expensive and inefficient to do the right thing.

    Thank you for putting up such a stink Joe, keep up the good work, this industry needs more soldiers like you!!!

  42. DavidButler | | #42

    response to Allison Bailes #27
    Allison wrote:
    > The HERS Standards allow confirmed ratings to use a default infiltration rate. That is, no blower door test.

    That was once true, but the default option was removed (for envelope & duct leakage) earlier this year as a result of public comments to RESNET Standard 301-201x. Steve Byers, myself, and several others actively lobbied for this.

    As you point out, only a portion of sampled homes must be tested but since the tested home is randomly selected, and a failure results in 100% testing, it's not appropriate to compare these with non-rated homes.

  43. DavidButler | | #43

    Here's my take on the ventilation debate
    Here's my take on the ventilation debate: I like Joe's approach for new construction. Unlike the ASHRAE 62.2 Committee, BSC is not encumbered by the political process inherent in consensus standard writing.

    What about older unsealed homes? As others have noted here and in other forums, there comes a point at which the prescribed MV rate would be overwhelmed by infiltration. That's not to say that very leaky homes will necessarily have good IAQ, just that it doesn't make sense to ventilate until and unless you get the home tight enough for it to actually do any good.

    Unfortunately, I see no way to define a threshold prescriptively that works for all, or even most homes. That's why we have brains, and why we do research. More of both are needed.

  44. CiaranM | | #44

    Yes David but what if our home had a brain?
    I am a builder in Canada and I am also an inventor. One of the projects I am working on is a product called Rhea or the recycling home energy appliance. Rhea is the Goddess of everything that flows so its a fitting name. Rhea is six major components built around the homes main plumbing stack including a hrv, a flash hot water heater and a central vacuum stacked bottom to top on the right side. The left side contains a waste air to water exchanger, a waste grey water to water exchanger and a fresh air to grey water exchanger. Rhea ventilates the entire house and uses the leftover heat from grey water to preheat the fresh air prior to sending it to the HRV. Rhea has the potential to be much more than the sum of her parts. I am planing to build a new home here in the near future and showcasing most of our 24 inventions. Rhea will play a pivotal role in this new home and will replace the homes thermostat and be responsible for so much more than any programmable thermostat on the market today could ever achieve.

  45. CiaranM | | #45

    When I designed Rhea I took into account how people live in their homes and adjusted Rhea to compensate for peoples behaviour. For instance people shower and refuse to run the bath fan because it makes the room cold and the noise bothers them, so now we have a ventilation problem. With Rhea we know you are in the shower because Rhea has detected heat in the grey water and is stopping it to remove the energy. Now Rhea knows to increase the rate of air flow from the bathrooms. Ceiling fans are obviously mounted in the ceiling and vented straight out, with Rhea we place the vent beside the toilet and draw air from there at a constant yet slow speed. Ceiling fans are designed to quickly vent the room and when you leave you also turn the fan off. Rhea ventilates 24/7 and at a very slow pace but it runs unlike the bath fans that usually remain off. Now if we look at how bathrooms are constructed these days we can see why I went this route, years ago bathrooms were plastered or drywalled with conventional products but now we have dense shield,aqua board and a host of other products designed for a moist environment. So today's bathrooms can handle moisture and this buys us time to ventilate at a slower speed where the temperature won't plummet and there is no noise in the room and the best part is its automatic and the occupants don't even have to concern themselves about it.

  46. CiaranM | | #46

    Martin I read your article on radiant barrier some time ago when I was researching radiant barrier OSB for another invention I was working on called STAR's or Solar Thermal-Air Roofing system. With this system we install radiant barrier OSB reflective side up on a new or existing home we then apply 2x4s on edge every 8 inches running the length of the roof and to those we cap with a reflective metal cap and then we apply a standard metal roof or you could sheet again with OSB and shingle. What we have left are 6.5 x 3.5 inch chambers running the length of the roof. Now we can draw air in from the bottom and duct it of at the top. We now have a way to keep the home cooler and we can take this heat and use it in a multitude of different ways, one of which can be to replace the homes stale air with preheated solar air.

  47. GBA Editor
    Martin Holladay | | #47

    Response to Ciaran Morris
    Lots of people have built rooftop solar air systems. They've been doing it since the 1940s. Some are glazed; some draw air from channels below metal roofing, as you suggest; and some draw air from a hot attic (with or without sloped glazing). All share the same problem: the economic value of the heat they provide is never enough to justify the cost of the equipment.

    In a cold climate, such a roof is often covered with snow when you need the heat the most, and the thermal output of such a system is zero. When the system's thermal output is greatest, no one wants the heat, because it's summer.

  48. CiaranM | | #48

    We took all that into consideration when we designed the whole system. First the cost to add this to your house is very low only a dollar a square foot extra, even if you have ST or PV on the roof it usually only takes up a small portion and this system is the entire roof. Then we added two methods we call STEM (short term energy management) and STEALTH (short term energy and long term housing). STEM is the heavily insulated exterior plenum that can be dressed to look like a chimney chase but is used to draw the air off the roof pulling it past a pex glycol coil allowing us to transfer the heat to a liquid. This heat can then be consumed by the home in a variety of ways or brought to STEALTH for later use. The fan and pump at the top of STEM can also run in reverse and melt snow from the roof which we also capture and use in a most unique way. Due to this reverse feature STEM has the ability to raise the top of its chimney chase exterior, opening vents at the top while sealing off the port to the STAR`s roof. This allows us to capture overnight lows by bringing in cold night air and transferring it into STEM`s hydronics which then stores this temporary cool source on the exterior bottom 3 feet of the basements wall. During the day when the home heats up this is the first source Rhea uses in her cooling strategy.
    I live in a strange place called Calgary Alberta and often my air-conditioner is running even though the temperature outside has dropped well below where my thermostat is set. This is because my home has no way of telling that this regular phenomenon has occurred. My mechanical system also has no way to take advantage of this situation either. So we are also designing this feature into STEM, allowing STEM to import air directly into the home while Rhea can then vent directly outside bypassing her air to air exchanger. These features along with all the other ones that I haven`t yet mentioned will give this home excellent control over its ventilation and minimize the homes carbon footprint by sourcing what`s available to it at or near the time the home requires it.

  49. GBA Editor
    Martin Holladay | | #49

    Response to Ciaran Morris
    Count me a skeptic. You can't take advantage of solar hot air channels without additional hardware; in most cases, you'll need ducts, blowers, and electronic controls. The heat is available at the wrong time of year, and it has a very low economic value.

    A home designer would get better returns on their investment by taking all of the money that your equipment would cost and investing that money in building envelope air-sealing, additional insulation, or better windows.

  50. CiaranM | | #50

    That should go without saying Martin, our next home will be built with ICF blocks have triple pane windows and Rhea is all about minimizing the holes in the building envelope. STEALTH is built under the homes attached garage, ( here the basement also runs around the perimeter of the garage) special plates are used to transfer the weight of the pile supporting the floor through the insulated floor of STEALTH and into the pad below, also the same plates transfer the weight from the concrete floor through the top layer of insulation and into the pile. These piles (usually 4 to 6) will be wrapped with hydronic pex pipes that run to STEM and to our IS Block system. This area that exists in every home built in this region can now be fortified with extra insulation and function as an ultimate heat dump. We can backfill like normal and store the heat in pit run or something similar. One thing we are considering doing is backfilling this void with carbon captured from the oil and gas industries practices, by lining the cavity with 10 mil poly prior to placing the carbon we can safely sequester 84 tons of carbon under every garage and use this heat dump to help regulate the temperature of the home and now we have a place to store low grade heat when it is available, don't forget by taking this heat away from the roof we also make the home easier to cool in summer months.

  51. Option7 | | #51

    "ASHRAE 62.2" great "rule of thumb" for masters of the obvious!
    I have been involved in semicinductor nano systems design and fabrication for 30+ years where you ALWAYS take into account all variables which in this case would be the sources of air intake through infiltration in an exhaust only installation. The new 6.2 standard simply suggests to homeowners to turn up the CFM to create a even more negative pressure environment and not care where the make up air is coming from along with whatever contaminants it brings into the living space. This is either extreme ignorance or they simply want to sell multiple higher CFM point of use exhaust fans in every home rather than a well placed supply air intake fan with filtration to insure the best air quality. Exhaust only ventilation systems are pure garbage when it comes to living space air quality unless you live in a building designed with strict materials ougassing limits such as in semiconductor nanofabrication facilities. Of course there are no homes that meet these strict criteria (especially older homes) so increasing infiltration air supply under the new 6.2 standard will bring more of every unknown contaminant you can imagine into the living space. Bathroom exhaust fans trade humid air for garbage, unhealthy infiltration air. The new 6.2 standard is the ignorant man's guide to bring in more unknown contaminants into the living space rather than advising homeowners on how to reduce infiltration/unknown contaminants.. If ASHRAE were credible they would have stressed the need to ALWAYS design HVAC systems with fresh air supply intake fan along with the desired filtration level to guarantee the air quality in the house the homeowner requires. In a supply only environment you create a pressurized living space so contaminants due to infiltration are eliminated and the only source for contaminants will then be from outgassing or particulate shedding of internal materials within the living space (paint, carpet, pet dander, dust, etc). The balanced or supply only systems approach should be strongly recommended over exhaust only systems such that total exhaust flow rate should never be higher than the incoming filtered supply or intake air in any structure if you are concerned with air quailty.
    Instead of trying to steer homeowners toward methods to eliminate the negative effects of "infiltration" in a negative pressure living space it simply tells them to increase the flow rate of poor quailty "infiltration air". I question the motives of the people on the 20 member panel who voted for this standard and wouldn't take their advice on anything related to HVAC system design. They are either ignorant or simply Using the 6.2 standard to promote every type of ventilation/make-up air product made by interested manufacturers (exhaust only, balanced or supply only systems). I believe it is the latter since It appears the 6.2 standard benefits the manufacturers and shady contractors. A reputable HVAC contractor would explain to their customer that the 6.2 standard for exhaust only systems is the worst system you could install unless you are only concerned about removing moisture from a bath or smoke from a cooktop.
    Unfortunately "do it yourselfers" would just upgrade their bathroom vents to higher CFM units which is the easiest to do but creates an increase in unhealthy contaminants. ASHRAE doesn't care about this because they will simply address the poor air quality later after homeowners have spent good money to upgrade their exhaust only systems only to find they have created healh problems that will force them to spend more money on one high quality controlled air supply system they should have installed in the first place rather than waist their money on the worthless upgrade of exhaust fans based on higher CFM suggested in the ASHRAE standard.
    If I were a shady HVAC contractor I would give a cooy of this standard to evey customer to tell them "Your exhaust fans are "undersized" and could result in expensive mold growth and dangerous levels of indoor air quality plaguing people with alergies or leading to alergies down the road due to prolonged exposure". The exact opposite wouod be true. The increase were raise the contaminant lebel and their health risks.

  52. GBA Editor
    Martin Holladay | | #52

    Response to Joe Consolini
    In fact, researchers who have studied exhaust-only ventilation systems have not found evidence of "unhealthy contaminants" in the makeup air. There is no evidence for your assertions; please cite a study.

  53. AmadeusMozart | | #53

    1) All theories aside: The only way to know if you are ventilating enough is to measure the CO2. (and perhaps other pollutants). 2) When we build our existing home I build my own ventilation system since we were very unhappy with a commercial system that we had previously. I was told that what I wanted to do would not work, however, it has been working like a charm. We could not be happier and we will do the same again in a new place we are going to build. My setup is to extract the stale air everywhere and only have one spot where the outside air gets supplied: above the heater. Then the cold air will mingle with the hot air from the heater and work its way through the house. (The reasoning behind this is that draft will make you feel colder - remember the ceiling fans? The only draft is now where the heater is where no-one sits, lies or spends their time, extracting air does not create a draft.)

    PS we live in a single level dwelling.

  54. johnosterman | | #54

    One year ago I moved into a 1400 square foot, 3 bedroom condo recently built to the new ASHRAE ventilation standard with ceiling ventilation. This new standard requires a ventilation rate of 72 cfm for my condo or approximately one air change every 3 hours. At this rate, the relative humidity in my condo is essentially the same as outside: under 25% in the winter (I live in Canada) and well over 70% during heat waves and rainy weather in the summer. ( I have had to install both a humidifier and dehumidifier. ) Moreover, I have asthma, but during SMOG and smoke alerts (we've had some forest fires) I get the same bad quality air indoors that they are warning us about outdoors! These new standards make no sense; they waste a lot of energy and make the indoor air quality of my home worse than it would have been using the old recommendations.


    1. exeric | | #55

      Hi John,
      This may be a sensitive subject in these parts but I think this article and its recommendations are quite outdated. I seem to recall even Martin saying that he's changed his mind recently on exhaust only ventilation. (Please correct me if that is wrong, Martin.) In my own house I originally went with a bathroom exhaust fan to ventilate the house at the ASHRAE recommended rate as part of a Deep Energy Retrofit of the house. The other part of the retrofit was tightening up the house substantially to a blower door measured 2.25ACH50. It quickly became obvious that the bathroom exhaust fan just was not enough ventilation as the CO2 level quickly went over 1000 ppm and kept going up with only one individual in the house. I added an ERV and it now stays between 500-600 ppm. My belief from my own experience is that any house with an ACH below 5, this is just a guess, probably deserves an ERV or HRV if the AC system itself doesn't supply fresh air.

      You may be able to get an acceptable ventilation rate without one but at a cost of bringing in air temperatures and humidity you don't want. It would depend on the climate. I think in most climates a fairly tight well insulated house deserves an ERV or an HRV

  55. Jon_R | | #56

    > make the indoor air quality of my home worse

    An ERV will cause less moisture transfer than a HRV. But I'd say that a dehumidifier and sometimes a humidifier is the new standard. I'm sure that for most pollutants most of the time, your air quality is better or the same. Good filters are needed when outside air is bad. Preferably part of the ERV/HRV but standalone interior units are an option.

  56. exeric | | #57

    "But I'd say that a dehumidifier and sometimes a humidifier is the new standard."

    When did this happen? Considering the energy cost of running a dehumidifier and the problems with introducing water vapor into the inside structure when using a humidifier this does not seem right. My Panasonic ERV uses 40 watts continuous for a 1000 sq ft house. It's always better to eliminate those complications and problems by using an ERV'HRV before they occur in my opinion. It seems to me a humidifier and/or a dehumidifier are band aids in most climates, (maybe not in the south) for deficiencies in the structure. Of course they may be required as a last resort. But that is what they should be - a last resort

  57. johnosterman | | #58

    Thanks for your comments, but it's a 150 unit complex and I have no control over the system design that was installed or the filters. I think that because of this standard, they're simply blowing too much air. (PS: I agree with the 'band-aid' comment!)


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