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Integrating an ERV with an Air Handler

Engineers at Steven Winter Associates are developing a new type of heating and ventilating appliance

A new type of heating and ventilating appliance is being developed by engineers at Steven Winter Associates. The appliance will integrate an energy-recovery ventilator (ERV) with an air handler that distributes warm air for heating and cool air for air conditioning.

Everyone pretty much gets that continuous (or very frequent) ventilation is necessary in high-performance homes. And — at least in theory — most people get why balanced, heat-recovery ventilation is better than ventilation that is unbalanced or lacking heat recovery. But the devil’s in the details.

A couple years ago, Steven Winters Associates started an R&D project with funding from DOE’s Building America program, and one of the first steps was interviewing several developers (single- and multi-family residential developers, mostly on the East Coast) about ventilation. For none of these developers were heat-recovery ventilators (HRVs) or energy-recovery ventilators (ERVs) standard [1]. They all had some experience with ERVs, however, and when asked about these experiences the word “nightmare” came up shockingly often.

The ERVs on the market now can certainly work well in the right application, but we see problems more often than not. One of the biggest challenges is trying to add ERVs on to central heating/cooling systems in homes. Most ERVs aren’t really designed for this, and here’s what we see:

  • Ducts connected to the wrong places! Outlet and inlet ducts get reversed, or the supply air from the air handler unit (AHU) getting exhausted (sad how often this happens).
  • ERVs are attached to supply and/or return trunks of the AHU. Unless the AHU fan is running constantly (or whenever the ERV is turned on), outdoor air comes into the AHU and is sucked right back out the ERV exhaust.
  • If the AHU fan is turned on, the relatively small fans in the ERV can’t successfully compete with the big AHU fan. People don’t get the ventilation flow rates they want and/or the flows are very unbalanced.
  • AHU fans can use a lot of electricity. Hundreds of watts is common — I’ve measured over 1 kW (though this is changing — more below).

Even if installers follow manufacturer instructions for attaching ERVs to AHUs, they could still end up with low flows, unbalanced flows, or high electricity consumption. Through this DOE R&D effort, we’re trying to do better.

Developing prototypes for a new integrated appliance

We’ve been working with Mitsubishi Electric Trane, CORE Energy Recovery Solutions, and Therma-Stor to design an ERV that’s truly integrated with a small, efficient forced-air heating and cooling system. The small and efficient are key pieces, as we’re making use of the AHU fan to move outdoor air around the space. Residential heating and cooling loads have come way down, and small, efficient, variable-speed fan motors are more common (and less expensive). Our prototypes have been integrated with a 1-ton Mitsubishi air-source heat pump (with a full-static AHU). This has more than enough capacity for most new apartments (built to reasonable codes), and it’s even enough for many very efficient single-family homes. We think it could work pretty well for systems up to 2 tons, but we’re not looking to go beyond that. The ventilation flow rates and heating/cooling flow rates might be too dissimilar, and larger AHU fans would likely use too much energy.

Our integrated ERV has both outdoor air and exhaust air fans, but they’re efficient, variable-speed, and they’re sized to work with the AHU fan. So even when the AHU ramps up to high speed for a big thermal load, the ERV fans adjust to maintain desired ventilation flow rates. With the Mitsubishi AHU we’re using, our prototypes delivered 50-120 cfm of balanced ventilation using 40-80 watts including the AHU power. The cross-flow heat exchangers from CORE provided 70% sensible recovery at 120 cfm (above 80% at 40 cfm). In the summer, total energy recovery was around 45% at 120 cfm and 60% at 40 cfm.

For a bit more info, check out our 2-page summary sheet. We’re still working with partners to optimize size, power consumption, control features, cost, etc. A patent is pending, and this is not on the market yet. But if you’re interested, we’d love your feedback. We’ve posted a quick survey to gather some information about what folks use now for ventilation, what features they’d like to see, capacity, price-points, etc. It’s anonymous (unless you want to give us your e-mail). Feedback is welcome!


[1]  HRVs transfer sensible heat only (temperature); ERVs transfer sensible and latent (moisture) heat. Because I don’t want to write “HRVs or ERVs” all the time, I’m just going to use “ERVs,” but the issues are very similar for both systems.


Robb Aldrich is Principal Mechanical Engineer at Steven Winter Associates in Norwalk, Connecticut. Robb focuses on building energy systems: researching new technologies, monitoring performance of systems, and working with stakeholders across the country to create better, healthier, more efficient buildings.


  1. Expert Member
    ARMANDO COBO | | #1

    I believe in stand-alone systems to provide balanced ventilation, as most homes require between 40-80 cfm of continuous ventilation. Spot ERVs are ideal for single family homes as they are affordable, easy to install and energy efficient, and you don't have to deal with any integration with the HVAC system.

  2. Jon_R | | #2

    No doubt that there are considerable savings to be had by not needing separate ducts.

    There are already constant flow H/ERVs on the market (eg Zehnder Novus 300) that are capable of more pressure than the typical furnace AH. So one should be able to connect ERV supply to AH supply and ERV return to AH return and still maintain balance and desired ventilation rate - with and without the AH being on.

    There will be a short-circuit path through the AH when it's off - but perhaps the air filter creates enough resistance to block most of this flow.

    Other than integration (which makes sense), does this new system do more than what is already possible?

    1. robbaldrich | | #8

      To clarify, the plan is for the AHU fan to be ON whenever you're ventilating – often 24/7. This certainly has electric energy implications, but small, variable-speed fans can use very little energy. In the 1-ton Mitsubishi system (in which we’re testing prototypes), the AHU fan uses 30-35 Watts on low speed. We don’t envision this working well with much larger, less efficient AHU fans; the electricity hit would be too big.

  3. user-723121 | | #3

    Back in the day (1980's) controls were not available to sequence HRV run time, as in 20 minutes on, 40 minutes off. Continuous running HRV's brought in too much fresh air, overly drying the house and had an energy penalty. If I remember correctly we used a 24 hour dial timer with pins to run the HRV and this would be overridden with remote timers in the baths, kitchen and laundry. We used a separate duct system in the double wall homes and if the forced air ductwork was utilized the HRV supply air was introduced into the furnace supply side. It was thought the cold HRV air into the furnace return would cause problems with the furnace heat exchanger by over cooling it.

    1. tundracycle | | #6

      Continuous running HRV's brought in too much fresh air,

      How much is too much? How much fresh air is needed in a house?

      1. GBA Editor
        Martin Holladay | | #7

        W. Ramsay,
        Here is a link to an article that addresses your question: "How Much Fresh Air Does Your Home Need?"

        1. tundracycle | | #13

          Yes, we have a standard. But does provisioning a system by that standard produce healthy enough indoor air? If a system designed to those specs results in 1400 ppm CO2, is that good enough? Or do we need 1000 ppm CO2? Or 400 ppm CO2?

          Will a system designed to ASHREA 62.2 reduce other VOC's to a healthy level? What level is that for what VOC's?

          1. schreib77 | | #17

            All good questions. Here is my answer from MY home building experience:
            New home last year with NO AHU unit, slab on grade & hydronic heat Mech Vent system: 50 CFM fan bringing in Fresh air and a 2nd identical bath fan exhausting. House and occupants dictated 45 cfm mech. vent was required min. 24/7. With my cheap fan system($130) I could attain the standard but dried the crap out of my home-- often low 20% range RH! in winter.
            I just installed a panasonic ERV(NOT HRV) and my humidifier has turned itself off because we re-capture the humidity in the exhaust air and return to home in Supply. My house "blows" 1.0 in the blower door test.
            As to CO2: I bought a $300 Dwyer CO2 meter. Simple mech. bath fan system usually hit 850 CO2 when on continuously but the other "half" of air quality, RH, was NOT attained as noted above. The new ERV solved the RH problem(too dry) and keeps the CO2 around 950 ppm. Maybe higher than what some may like to have but I have seen no problems and Martin has offered in his blog elsewhere, I recall, that a number around 1000 ppm is likely "good."

            For the ERV, I bring in fresh air to only one point: Master Bedroom right in front of my Mitsubishi Mini-split head. If the incoming air is a bit cool the head re-heats and mixes it in the far corner away from the bed. Works great. CO2 readings taken in middle of home-- NOT right there in bedroom. CO2 numbers in BR are down around 850 ppm.

  4. contdan | | #4

    One of the key benefits of a separate ERV is to take the stale are out from bathrooms, and other areas specific areas where fresh air is not needed. The system described above seems to just provide fresh air to the entire HVAC system, which may be ideal for smaller projects. Is there any consideration to also allowing stale air ducts to be tied in from bath exhausts?

    1. robbaldrich | | #16

      Yes there is. In the images here, the return air is shown to split between ERV exhaust and return to the AHU. Instead of splitting exhaust from return air, the lower, exhaust intake can have 4" or 6" collars to run ducts for local exhaust. The exhaust fan is sized for some considerable pressure, so pulling through reasonable exhaust ducts won't be a problem. Whether or not it's wise to recover moisture from bathrooms is another issue (we're also thinking of an HRV version down the road).

  5. sethw | | #5

    While I can seem some problems, I really respect the effort to simplify and consolidate systems. This could control marketplace resistance as well as unreasonable cost increases.

  6. Dennis_Miller | | #9

    I wish this a combo product as described in the article was already stable and on the market as we are soon building a "pretty-good house" and would be interested.

    So it seems to me that many people are quite happy to heat/cool their homes with a minisplit ductless heat pump (or whatever the proper term is). So if a house seems to be heating and cooling well with two or three interior units, is it an outrageous thought to think that an independent ventilation system could be added to this scenario? The interior units control the temp while the ventilation unit recycles some of the air. Is this reasonable, or hopeful thinking, or a air handling disaster waiting to happen?

    1. schreib77 | | #18

      See my reply to a post above, my post #17.
      I did almost exactly what you are proposing. It works. Although my main heat source is a boiler(hydronic heat in concrete slab) in a warmer climate I could have chosen complete mini-splits. Living in Minnesota hydronic as the main heat works really well. I mostly have the mini-split as my AC in the 3 weeks during summer! However, it was very handy in my application for placement of the colder fresh air coming in from the Panasonic ERV.

  7. GBA Editor
    Martin Holladay | | #10

    André Fauteux, a GBA reader from Québec, read this article and sent me the following comment by email: "What’s new about it, except the ERV? Lifebreath has made its Clean Air Furnace for years."

    I'm posting André's comment in case Robb Aldrich cares to respond.

  8. robbaldrich | | #11

    The main difference is that our system will integrate with ducted heating/cooling systems (preferably small-capacity heat pumps with efficient, variable-speed fans). This new system won’t provide heating/cooling itself. The decoupled nature will allow you to change ventilation flow set points, and these rates will be maintained regardless of what the H/C system is doing (especially important when the H/C fan changes speeds). So it’ll hopefully more versatile, but I know some very happy Clean Air Furnace users.

    1. GBA Editor
      Martin Holladay | | #12

      Thanks, Robb.

  9. user-6813968 | | #14

    I live in the Raleigh NC area and have recently completed a 3 br two bath plus office 2095 Sq Ft new custom home. The homes is a single level on a slab with 2X6 exterior walls, flash and bat insulation, low E windows and is an Energy Star Certified home. We installed a ductless Mitsubishi mini split with four evaporators, in living room, and one in each bedroom. The office does not have an evaporator but temperature is within one degree of the other rooms. We also installed an independent Honeywell ERV system. The system is very energy efficient and does a great job of heating and cooling. I don't understand why now today's homes do not use this same system. There is a lot of energy loss in a central HVAC system through the duct work. Can anyone tell me why this is not the standard HVAC system in today's market. NC is a very humid area but right now as I type outdoor humidity is 94% and indoor humidity is 41%. It's a great system.

    1. GBA Editor
      Martin Holladay | | #15

      User 6813968,
      It would be useful to know your name. (I'm Martin.)

      You're preaching to the choir. Here at GBA, we have been advocating the use of ductless minisplits and balanced ventilation systems with dedicated ductwork for years.

      I'm glad you're pleased with your system, but it sounds as if the designer of your system went overboard. It's almost impossible for a 3-bedroom house measuring 2,095 square feet to have a load that requires four minisplit heads. I suspect your system is grossly oversized.

  10. schreib77 | | #19

    Robb, could you comment on this? Based on only what you display for your module it appears you split the Return air with a single, non-moving baffle. It seems like kind of a no-brainer to move the baffle dynamically with a closed loop controller to modulate output and provide REAL control. Your control variable could be maximizing delta T across the exchanger with 2ndary control via pressure inputs on the system. Doing so takes the scariness out of the whole thing for technicians and optimizes the efficiency. Not knowing all how this works and what your controls already do I may be off in suggesting these variables but the idea of dynamic baffle control seems useful to your patents!

    1. robbaldrich | | #38

      Hi Brian - I'm afraid I don't get where you're coming from. Right now, ventilation flow rates are controlled by changing the speeds of the variable-speed fans (outdoor air & exhaust air fans). In prototypes, we're using constant-flow fans (flow based on the input voltage). These are pricey, but we hope to use them in production too. Early versions might have a simple dial/voltage divider, but it could accommodate more elaborate controls (DCV, etc.). Shouldn't be much trouble for technicians; the fans provide constant flow over an impressive range of pressures.

      Feedback on control functionality is welcome. Advanced controls certainly possible, but certainly more costly.

      1. schreib77 | | #39

        Robb, my comment may not be meaningful based on lack of full understanding of your system. However, I was only referring to the fact that the RETURN flow (the orange arrows, ONE fan right?) is split at your unit with no control over the ratio-- being this split occurs at a non-moving split junction. I was suggesting that control flexibility could be gained by making that split variable so the ratio could be modulated between flow going into your ERV media and that returning to the AHU. That flat piece of metal could be moved so as to modulate. Such modulation allows more or less to return to the AHU vs the exchange media dependent upon some variable you choose to enhance control.

        1. robbaldrich | | #49

          Gotcha - sort of. In early prototypes we tried using one fan and modulating dampers, but that proved to be too limiting. So latest prototypes use two small, variable-speed fans: outdoor air and exhaust air.

  11. user-6813968 | | #20

    Martin, the contractor that installed the mini split and the ERV system was not very competent and it took him about 10+ return trips to finally get it right. Initially he installed one Mitsubishi MXZ-4C36NA2 condenser (3 Ton) and four evaporators, MSZ GL-15NA in living room, MSZ GL-09NA in master bedroom, and MSZ GL-06NA in the other two bedrooms. The thermostats he installed were inferior and the temperature sensors were located in the evaporators and they did not hold the temperature at the set temperature. I wasn't very happy with this and they finally installed better thermostats that had the temperature sensor in the programmable control unit that I installed on the wall in each room. and they had to add a unit on each evaporator that would communicate with the new thermostat controllers. After that the system would keep room temperature at setting as long as it wasn't too hot or too cold. So then the issue was the condenser was not big enough to keep up with extreme hot or cold I would set the thermostat for 72 and it would never get there same thing in the summer. Finally he installed two H2i Hyper Heat condensers one MXZ-3C30NAHZ2 (3 ton) and one MXZ-2C20NAHZ2 (2 ton). The larger runs the living room and the Master Bedroom and the smaller unit runs the other two bedrooms. Finally we have a system that controls the room temperature at the set temperature and can keep up the with heating and cooling demands.

    Tim Corcoran

  12. AndyKosick | | #21

    I assume there are filters on the core but is there a filter for the bypass air or would that additional to this unit?

    1. robbaldrich | | #30

      All air pathways are filtered: outdoor air entering core, air entering AHU, and exhaust air (to protect the core and blower). Not sure what you mean by bypass air, but I think we're filtering everything we need to filter.

  13. user-1102988628 | | #22

    Interesting. I just paid $$$$$$$$ for a SW mechanical engineer to design a system in my new highly insulated (exterior insulation ++++) house and he spec'd an ERV tied into my HVAC system. Extremely frustrating and now i learn that others in the same company are campaigning against this ventilation method.

    1. robbaldrich | | #29

      This system isn’t available yet. From a strict performance standpoint, a separate H/ERV with separate ducts will usually deliver ventilation more consistently than will an add-on system with the central AHU. But separate distribution requires more time, money, and space. We go over these issues with our clients, but a separate distribution system is not always possible or practical. These are challenges we hope to address with the system in the works.

      1. user-1102988628 | | #35

        There wasn't much of a discussion... just a recommendation. I have decided to install a Zehnder and disregard the SW plan. I also think that using a couple of pairs of the Lunos systems would have been more beneficial than using HVAC ducts. Even if your theory is true that sometime combined systems are possible, in practice they do not work. My experience is that most of the HVAC people do not understand how to install combined systems. The probability of correct Installation should be a significant consideration when specifying combined systems for reliant customers.

  14. tundracycle | | #23

    Unofficially a couple of folks at Mayo said they’d shoot for no greater than 500 ppm CO2 and that they believe that is what CERV is set for. They think current US fresh air ventilation standards are much too lax.

    1. GBA Editor
      Martin Holladay | | #24

      W. Ramsay,
      To the best of my knowledge, the CO2 sensors on the CERV have a default setting of 1,000 ppm. For more information, see "A Balanced Ventilation System With a Built-In Heat Pump."

      For information on a research project which used the 1,000 ppm benchmark for CO2 as a reasonable target, see "Ensuring Fresh Air in Bedrooms."

      1. tundracycle | | #34

        Thanks Martin. Good articles. I may have misunderstood their CERV comment.

        From the rather limited reading I've been able to do on this topic I've come away with the impression that our 1,000 ppm target is a guess, we really don't know what the health impact of various CO2 levels is, but closer to atmospheric levels (402 ppm?) is likely much better and perhaps critically better, and there are many other contaminant bits that we may need to be concerned about as well.

        It's interesting that mechanical air movement, even with a ventilation system, didn't work as well as opening a door. I think I'd agree with the comments that these homes must have had a poorly designed or implemented duct system.

    2. Trevor_Lambert | | #25

      Given that atmospheric CO2 is around 450ppm, I would say 500ppm is not a realistic number, unless your system includes some kind of CO2 scrubber. I've found that <650ppm is fairly easily maintained, most of the time.

    3. Jon_R | | #26

      But note that a single person in a large house would produce low ppm CO2 and yet there might be significant danger from other pollutants. CO2 is a poor proxy for other pollutants.

      1. schreib77 | | #28

        No, the present consensus is that CO2 is, in fact, a good proxy; the only reasonable proxy that can be sensed without excessive cost. Sensing the organic pollutants you allude to is NOT simple, is not reasonable, and is very expensive. CO2 was chosen by ASHRAE and other air quality bodies specifically because it IS a proxy that can work.

        You should spend $2 or $300 and buy a CO2 meter ; take readings around your house for a year or so like I have. Then, you may appreciate its efficacy.

        1. Jon_R | | #31

          I have one - and what I said is correct. I suggest you open a can of paint thinner and see what your CO2 meter says about the need for more ventilation.

          1. Trevor_Lambert | | #33

            The use of CO2 as a proxy does depend on a couple of premises, most importantly that the house is occupied by a typical number of people and that the amount of other airborne pollutants are also typical. With this in mind, it's a useful tool. I used it to set a baseline ventilation rate, but am obviously aware that if I start cooking, painting, sanding, etc. in the house that additional ventilation is needed. CO2 is the only pollutant that, given ideal conditions, will constantly rise without any occupant behaviour (aside from just being there). It's certainly a better proxy than no proxy at all.

            Monitors for HCHO, TVOC, PM2.5, PM10 are actually available for pretty reasonable prices as well.

          2. schreib77 | | #41

            Well Jon, not sure what exactly you are implying but implying you are!
            some pointers you may not be fully aware of:
            -- CO2 meters are NDIR type-- non-dispersive infra-red. They sense the 4.26 µm band of absorption and compare background absorption to what CO2 blocks from the detector and filter.
            -- OTHER gases passing down the sensing tube can also elicit a response but they do not need to be CO2. For example, if the paint thinner you have in mind has an absorption band in this critical area it will affect the reading.
            -- This reading change does not mean that since the READOUT on the meter goes up or down that CO2 goes up or down. It means that constituent gases have passed by the sensor and affected absorption in the 4.26 µm band.

            The CO2 meter does not say anything about "needing ventilation". It is simply another dumb computation that puts out numbers requiring intelligent, human interpretation and subsequent action, if required!

            "I have one - and what I said is correct. " What you said earlier is simply false. Listen to facts not your guessing. Read up on this technology:


    4. schreib77 | | #27

      Mr. Ramsay:
      Ocasio- Cortez, senator from NY, would like to have clean air standards that bankrupt every economy in the world because the world is going to end in 12 years too.

      Do the Mayo folks know anything about air handling, air quality, or are they just shooting from the hip?

      The folks here have spent a lot of time considering CO2 and air quality in general. Perhaps the Mayo folks should buy a CO2 meter and walk around a few "real" homes, including their own, before stating what they would suggest. 500 ppm CO2 is basically the constituent makeup of outside air. Tight homes approach totally enclosed living volumes so when living beings occupy them gases emitted build up while reducing oxygen levels unless directly removed. Two ways: feed in a low level outside source(~ 450 ppm CO2) or close up the space and recirculate the gases through a scrubbing system that controls all gas levels. The latter being a multi-million dollar system.

      At NASA they chose to install CO2 scrubbers that adsorb the CO2 and create oxygen from water to keep the levels under control. Such technology is not practical on earth.

      Their OUTSIDE air standard is not a likely solution and not. . . a very considered "thought".

      1. tundracycle | | #32

        I've no idea how much they know about air handling but these are a well regarded pulmonologist and epidemiologist so I'm guessing they might know something about air quality and what is good/bad for our bodies.

        What they know about air handling systems is irrelevant though. What we need from them and the rest of the medical community is what air quality do we need in our homes and buildings and then work to achieve that in the most energy efficient way. My guess is that in many cases the best solution to achieve the best air quality may be to turn off the air handling system and open a bunch of windows - something we're not so good at doing in the U.S.

  15. user-6813968 | | #36

    People used to open windows in the Summer time because they had to with no AC. If you live in Southern California or Hawaii that is an option for most of the year but the rest of the country it's too cold in the winter and too humid in the summer to leave the windows open.

    1. tundracycle | | #37

      It is perhaps a lot like our penchant for driving to a store that's only 1 mile away, getting irritated when we can't park our car directly in front, and then wonder why we're so unhealthy due to lack of activity. We want out houses to be 71°f and 42% RH (both +/- 0.5%).

      In reality we can open windows for a good chunk of each year in most of the U.S. And even more days if we have a whole house fan - assuming we're OK with a bit more variation in temps and humidity.

      In theory this should provide much better indoor air quality and use considerably less energy. How much of a health difference this would make I don't really know beyond it likely being healthier.

      It'd be interesting if energy (petrol, NG & electric) costs rose considerably and everyone had to begin paying for 100% of their healthcare expenses. I'd guess we'd see a lot of open windows and fewer cars on the road.

      1. schreib77 | | #40

        Much of what you say makes a lot of sense: open the dang windows and let some fresh air in. True for much of Minnesota for the majority of summer but many folks leave the house shut up-- we open the windows like you would. However, back to your point about the Mayo docs. OK fine, they are experts, but keep in mind, experts in human disease causation, specifically, pulmonary(lung related). So, they will recommend what they know is the highest likelihood for folks with COPD or emphysema-- only a tiny minority of the population. Home HVAC systems are designed for the majority of us; those with ill health need to be in hospitals, sometimes in the critical care wards with, guess what, a controlled environment. They likely have not studied nor are experts on humans living in controlled CO2 or specific indoor environments so I have a hard time taking these specialists as knowledgeable in this area. Even if they did the probability of the average human taking their advice is as likely as morbidly overweight people reducing their fat intake. This world of engineering is not like your theoretical world. Things are dealt with in ways that are truly CONTROLLABLE with technology as it is available today.

        "Live in the open air" is basically what they / you are recommending but that is not practical in either cold or hot weather. As modern humans we have adapted: AC in hot / heating in Cold weather. Both require closing off the undesirable temperature by enclosing the humans. The simple reality is there are tradeoffs-- have comfort but lose the fresh air(normal gas ratios of outside air, only OUTSIDE air pollutants) OR keep these ratios with low inside air pollutants and temperature comfort at VERY HIGH COST-- NASA space station breathing air control. AKA the new GREEN deal being proposed by the NY socialist: tax $500K per person in a vain attempt to reverse global weather swings. Sorry, that just won't fly.

        1. tundracycle | | #47

          There is still very much that we don't know. We do know that the healthiest and longest lived people in the world all live in temperate climates and spend a lot of time out-of-doors. And we know that people in the U.S. are among the least healthy, including of diseases that are likely be caused by poor IAQ. How much is fresh air and how much is activity is unknown.

          BTW, Sweden and Netherlands are both fascinating pseudo exceptions of sorts. They're far from the healthiest but are healthier than would normally be predicted. Both are also known for people being more active than average and spending more time out of doors than average.

          We also don't know about exposure. Is there a great advantage to 6 months of fresh air even if the other 6 months are inside with poor IAQ? Likely, but I think we're still not sure and may find that it is very much daily exposure and not cumulative.

          1. Dennis_Miller | | #48

            I agree that we should pursue IAQ as much as possible, and personally I am an active homeowner that opens windows regularly. I also agree that the average homeowner cannot be counted upon to bother with windows.

            I would also say that we are far from the least healthy, but we are still way down on the list, like 30th out of all the nations in the world, even the little tiny ones that hardly anyone has heard of. But of course there are many factors involved in healthiness and I would suggest that while IAQ is a factor, it is generally way down on the list of causes. Probably the biggest things in the US are behavioral issues. The US is #1 in obesity, the opioid epidemic is mostly a US phenomenon, compared to the world we are about average in smoking tobacco, we have 10 times more McDonalds than Canada, we have a lot of meth users whereas the UK has hardly any, and so on. Make a pie chart of health issues for the US and I suspect IAQ would be a tiny slice, but still worth addressing.

          2. Expert Member
            Dana Dorsett | | #50

            I suspect one evening spent at any oud bruin cafe in Amsterdam is worth a month of heavy breathing on the average couch in 'merica, from a indoor air quality and health risk perspective. The brown walls are painted with centuries worth of tobacco smoke, and it seems every other patron seems determined to do their fair share of the ongoing painting. :-)

            Breaking down longevity by climate in the US is complicated due to the number of times people move. But Hawaii is #1 (temperate, but on the very warm side), followed by Minnesota (not so temperate), then Puerto Rico (another temperate but very warm location) then Connecticut (not exactly temperate) and California (variable, but mostly temperate), then Massachusetts (not so temperate.)

            Longevity is also highly correlated with relative wealth, and access to quality health care, which both Sweden & Nederland have in abundance compared to the US. Among the ten lowest longevity states & territories of the US most are in temperate climates, but have lower average income, higher poverty rates, and less access to quality health care than states like MN/CT/MA, and the rest of the 10, most of which are in colder but wealthier states. The only top 10 longevity state/territory with higher poverty / lower personal wealth is Puerto Rico, which has offered free & very low cost health insurance for poor & indigent citizens for about 25 years, despite selling off the large public hospitals to the private sector during the same reform period.



      2. Trevor_Lambert | | #42

        "In reality we can open windows for a good chunk of each year"
        Ok, so that leaves a good chunk of the year that you can't. Which means you NEED a system that works when the windows are closed.
        "In theory this should provide much better indoor air quality and use considerably less energy." The first part of that is debatable, the latter is false. Unless you are okay with your house being the ambient outside temperature, which could be 0F/-18C or below, you are definitely going to use more energy with the windows open than closed.

        1. tundracycle | | #45


          - Natural fresh air cooling + ventilation (open windows) for xxx days per year is still xxx more days per year of significantly reduced energy usage and healthier IAQ than current?

          - Yes, we then need to tend to the other xxx days when outside weather is not very conducive to open windows (though I've been known to crack windows open for a bit on many winter days in MN). Q1: What bits does our indoor air then need to possess or not possess? Q2: How do we best achieve that?

        2. tundracycle | | #46

          "the latter is false."

          Really? If it's 76°f, 45% humidity, slight breeze and I choose to turn off my HVAC system and open windows instead I will not be reducing my energy consumption? Quite significantly?

          Just because it'll be cold tomorrow doesn't mean that I can't enjoy open windows today.

  16. MAinspector | | #43

    With all this talk about CO2 detection do we see future codes requiring a CO2 detector installed on each story, similar to CO/Smoke detection? I could see a CO2 detector communicating with the mechanical ventilation system and even sending an alarm if levels reach a certain threshold. The way forward needs to include the understanding that the average homeowner buying the bulk of new homes being built has absolutely no clue about mechanical ventilation, air tightness, etc. I constantly see situations where homeowners move into a new house and turn off the ERV because the air coming in was cold, or hire an electrician to change the settings on the continuous bath fan because it was noisy. We need to keep in mind that most people are completely clueless to building science and I really don't see that changing.

  17. schreib77 | | #44

    Jon, a big difference here is CO will kill 'ya, CO2 will mostly make you sleepy as the % oxygen is reduced. I have not heard the CO2 has any documented long term health effects, though have not researched that.

    You are for sure correct as to most folks being clueless about general AQ but that will change as communication and news improve in this area-- 10 years out(?) before any real stuff happens? It will be forced by the market hopefully, not laws and "code". Folks building or owning new tight homes will start to become a higher minority and the market will reduce prices on CO2 detection to respond, CO2 sensors marketed with WIFI connectivity will appear like other wireless home control systems today, and eventually, all new homes will include them with the ERV / HRV. I would bet within 3 years they will be included in all ERV's. I would be surprised if Winter Associates does NOT include one with their integrated ERV.

    I see little need to have one on each story.

  18. PotatoEverett | | #51

    Oh man! Would love to try one of these out. Would need to be able to work horizontally and hopefully have configurable outdoor and exhaust ducts. How close do you feel these are to production? Would you like to have anybody test your prototype in Chicago? Any recommendations in the meantime?

  19. tkzz | | #52

    I'm wondering if a product like this exists now in 2023?

  20. tkzz | | #53

    How about 2024?

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