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Ventilation Rates and Human Health

Have researchers found any connection between residential ventilation rates and occupant health? The answer may surprise you.

Posted on Mar 29 2013 by Martin Holladay

Stuffy homes are unhealthy homes, while homes with plenty of fresh air are healthy. That’s been a commonly held belief for at least 200 years. In the mid-19th century, the connection between ventilation and human health was championed by sanitarians, a group of health experts who blamed the spread of bubonic plague and cholera on “miasma.”

According to Michelle Murphy, the author of Sick Building Syndrome and the Problem of Uncertainty, “Ventilation engineers had previously promoted the mechanical supply of ‘fresh air’ in the name of healthfulness, not comfort. The fight against foul air, excess carbon dioxide, and miasma … had allied ventilation engineers with public health reformers, called sanitarians, who sought to improve the living conditions of the worthy laboring poor by … legislating standards for fresh air in tenements, schools, and factories.”

The miasma theory of contagion was disproved in the 1860s. However, the connection between ventilation and human health is still trumpeted by various organizations, including “healthy house” groups and fan manufacturers. For example, marketing materials from Broan, a fan manufacturer, claim that “microbial pollutants like mold, pet dander and plant pollen along with chemicals such as radonColorless, odorless, short-lived radioactive gas that can seep into homes and result in lung cancer risk. Radon and its decay products emit cancer-causing alpha, beta, and gamma particles. and volatile organic compounds (VOCsVolatile organic compound. An organic compound that evaporates readily into the atmosphere; as defined by the U.S. Environmental Protection Agency, VOCs are organic compounds that volatize and then become involved in photochemical smog production.) create a toxic environment in your home.”

Similarly, a document posted on the website of the Healthy House Institute declares, “Ventilation is a critical component for home durability and occupant health.”

Since experts have posited a connection between mechanical ventilation in homes and human health for the last 160 years, perhaps it’s time to ask two questions:

  • Do we have any data that show a connection between residential mechanical ventilation and occupant health?
  • Do we know how much ventilation is desirable for optimal occupant health?

The answer to the first question is no, not really. And the answer to the second question is an emphatic no.

When pigs fly

The standard for residential ventilation in the U.S. is ASHRAE 62.2A standard for residential mechanical ventilation systems established by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. Among other requirements, the standard requires a home to have a mechanical ventilation system capable of ventilating at a rate of 1 cfm for every 100 square feet of occupiable space plus 7.5 cfm per occupant.. Among the members of the committee that developed ASHRAEAmerican Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). International organization dedicated to the advancement of heating, ventilation, air conditioning, and refrigeration through research, standards writing, publishing, and continuing education. Membership is open to anyone in the HVAC&R field; the organization has about 50,000 members. 62.2 were Joseph Lstiburek, a principal of the Building Science Corporation, and Max Sherman, a senior scientist at Lawrence Berkeley National Laboratory.

To understand the range of expert opinion on residential ventilation, it’s a good idea to consult both Lstiburek and Sherman, since they rarely agree. For years, Lstiburek and Sherman have been arguing publicly about optimal ventilation rates. When it comes to almost every ventilation controversy, these two experts are usually at opposite ends of the spectrum. When I asked both experts about the connection between residential ventilation rates and human health, however, I was surprised to discover that they agree.

I sent an e-mail to Sherman asking him about available data on the connection between residential ventilation and human health, and he responded, “I think there is no data. We have simulations.”

When I asked Lstiburek the same question, he answered, “There is no data. To determine the health limits for residential ventilation, they just take occupational limits and divide them by 10 or 100. There is no science to it.”

The evidence is indirect

According to a useful Web resource from Lawrence Berkeley National Laboratory (LBNL), Ventilation Rates and Health in Homes, “Very little research has been conducted on the relationship of ventilation rates in homes with the health of the occupants of the homes.”

Although researchers don’t have good data showing a link between residential ventilation rates and occupant heath, it’s possible to make inferences based on indirect evidence. The LBNL Web site notes, “From numerous experimental studies, as well as from theoretical modeling, we know that higher ventilation rates will reduce indoor concentrations of a broad range of indoor-generated air pollutants. Because exposures to some of these air pollutants, for example, environmental tobacco smoke and formaldehydeChemical found in many building products; most binders used for manufactured wood products are formaldehyde compounds. Reclassified by the United Nations International Agency for Research on Cancer (IARC) in 2004 as a “known human carcinogen.", have been linked with adverse health, we expect that increased home ventilation rates will reduce the associated health effects.”

This expectation has not yet been confirmed by researchers, however.

Scandinavian studies

The three most frequently cited studies of the relationship between residential ventilation rates and occupant health were all conducted in Scandinavia.

One was a 1999 study by Norwegian researchers (Oie, L., et al., “Ventilation in homes and bronchial obstruction in young children,” Epidemiology, 1999, 10 (3), pages 294-299).

The second relevant study was a 2004 study by Swedish researchers (Emenius, G., et al., “Building characteristics, indoor air quality and recurrent wheezing in very young children (BAMSE),” Indoor Air, 2004, 14 (1), pages 34-42).

The third relevant study was a 2005 study by Swedish researchers (C. G. Bornehag, J. Sundell, L. Hägerhed-Engman, and T. Sigsgaard, “Association Between Ventilation Rates in 390 Swedish Homes and Allergic Symptoms in Children,” Indoor Air, 2005, 15 (4), pages 275-280).

According to the LBNL web site, the 1999 Norwegian study focused on young children. The web site notes, “Low home ventilation rates were not associated with an increase in bronchial obstruction (i.e., reduced breathing airflows) in children. However, the increase in risk of bronchial obstruction resulting from other factors, such as building dampness, was moderately to markedly higher in homes with ventilation rates below 0.5 achACH stands for Air Changes per Hour. This is a metric of house air tightness. ACH is often expressed as ACH50, which is the air changes per hour when the house is depressurized to -50 pascals during a blower door test. The term ACHn or NACH refers to "natural" air changes per hour, meaning the rate of air leakage without blower door pressurization or depressurization. While many in the building science community detest this term and its use (because there is no such thing as "normal" or "natural" air leakage; that changes all the time with weather and other conditions), ACHn or NACH is used by many in the residential HVAC industry for their system sizing calculations.. In other words, having low ventilation rates increased the health risks from some of the building conditions, such as dampness, that are associated with indoor pollutant emissions.”

According to the LBNL web site, the 2004 Swedish study “found that the risk of recurrent wheezing in children was not different for houses with measured air exchange rates above and below 0.5 ach.”

Like the two other Scandinavian studies, the 2005 Swedish study also focused on children’s health. The Swedish researchers found no association between residential ventilation rates and asthma rates in children. However, the researchers found that children with rhinitis and eczema had lower ventilation rates in their bedrooms than non-symptomatic children.

The authors of the 2005 study admit several limitations to their findings. They noted, “Residential factors not associated with ventilation (e.g., smoking, socio-economic status) may have impacted the findings.” Moreover, “the associations between ventilation rates and asthma and allergy symptoms were not strong, perhaps due to the small sample size.”

What’s the bottom line? According to the LBNL web site, “In summary, the few studies that have directly investigated whether lower ventilation rates in homes are associated with a worsening of health have had mixed findings.”

Factories and office buildings

We have somewhat more data on the effects of ventilation rates on human health in non-residential buildings (factories and office buildings) than we do in homes.

When it comes to office buildings, “The available data indicate that occupant health and perceived IAQ will usually be improved by avoiding ventilation rates below 20 cfm (9 L/s) per occupant and indicate that further improvements in health and perceived IAQ will sometimes result from higher ventilation rates up to 40 cfm (18 L/s) per person. These findings are relatively consistent for office buildings located in cold or moderate climates, but less certain for other building types and climates.” (ASHRAE Journal, August 2002: “Ventilation Rates and Health,” by Olli Seppänen, William J. Fisk, and Mark J. Mendell.)

Three researchers — William J. Fisk, Anna G. Mirer, and Mark J. Mendell — studied the phenomenon known as “sick building syndrome.” The researchers reported, “Data from published studies were combined and analyzed to develop best-fit equations and curves quantifying the change in sick building syndrome (SBS) symptom prevalence in office workers with ventilation rate. … Based on these analyses, as the ventilation rate drops from 10 to 5 L/s-person, relative SBS symptom prevalence increases approximately 23% (12% to 32%), and as ventilation rate increases from 10 to 25 L/s-person, relative prevalence decreases approximately 29% (15% to 42%).” (“Quantitative relationship of sick building syndrome symptoms with ventilation rates,” by William J. Fisk, Anna G. Mirer, and Mark J. Mendell.)

It is far from clear, however, that studies of office buildings or factories have much relevance for homes. According to Joseph Lstiburek, “We have some Threshold Limit Values (TLVs) for some occupational stuff. But that is occupational stuff. If you are factory worker and you are working with a particular chemical that we know a great deal about, NIOSH probably has an exposure limit for that particular chemical. But, TLVs only apply in factories (i.e. “occupational exposure”); they do not apply in office buildings and certainly not in houses. … I am an order-of-magnitude kind of a guy and I sometimes divide the occupational numbers by ten when pressed for an opinion for office and residential exposure. But this is an arbitrary guess on my part. There is no health data that I have to go on. Why not divide by a hundred? Some folks do. Are they more ‘right’ than me? They seem to think so. The point is that we are making this stuff up. All of us.”

Asthma and high humidity

Several researchers have shown a correlation between asthma symptoms in children and humidity problems in homes. According to William J. Fisk (“How IEQ Affects Health, Productivity,” ASHRAE Journal, May 2002), “Many studies have found that the prevalence of respiratory symptoms associated with asthma are increased by 20% to 100% among occupants of houses with moisture problems, implying that elimination of these moisture problems would diminish symptoms by 17% to 50% in these occupants.”

Most of these homes with serious moisture problems (for example, leaking roofs, plumbing leaks, or moldy walls) are substandard homes occupied by low-income families. While increased ventilation rates might be one way to tackle these problems, the homes may need more direct interventions instead — for example, roof repairs, plumbing repairs, or the installation of polyethylene on the crawl space floor.

Moreover, damp living conditions are only one factor associated with asthma symptoms. Other factors include the number of pets in the house and whether or not family members smoke tobacco.

Ventilating during hot, humid weather

When it comes to determining ventilation rates for U.S. homes, it makes sense to be wary of the conclusions of Scandinavian researchers — unless, of course, you live somewhere in the U.S. with a climate that resembles the climate of Sweden.

The studies that show an association between homes with humidity problems and asthma symptoms in children lead some healthy-house advocates to promote high ventilation rates. That might make sense in Sweden in January, when outdoor air is dry. But the same advice can’t be applied to Houston in July.

According to the LBNL web site, “A higher indoor humidity, which, in turn, can lead to more indoor dust mites (an important allergen source) and to a greater risk of indoor mold growth, is another potential consequence of increased ventilation rate. Indoor humidity will increase with ventilation rate only when the outdoor air is more humid than the indoor air, e.g., during hot humid weather, and when the building mechanical systems also do not dehumidify sufficiently to counteract the effects of increased moisture entry. When outdoor air is less humid than indoor air, e.g., during cool winter weather, more ventilation decreases the indoor humidity.”

Overventilation carries an energy penalty

Healthy house advocates often sing the praises of high ventilation rates. But it’s important to remember that overventilation has several downsides.

The penalties associated with overventilation are summed up succinctly by William J. Fisk, Douglas Black, and Gregory Brunner, in an article titled “Changing Ventilation Rates in U.S. Offices: Implications for Health, Work Performance, Energy, and Associated Economics.” The authors wrote, “Providing more ventilation increases building energy consumption, increases the related emissions of carbon dioxide, and contributes to climate change. Modeling of the U.S. commercial building stock indicates that 6.5% of all end-use energy (3.2% in offices) is for heating and cooling of mechanically-supplied outdoor air ventilation. … One can estimate that an additional 3% of total end-use energy is used to heat and cool infiltration air, thus, an estimated 9.5% of end use energy is required for ventilation.”

What do you do when outdoor air is polluted?

It’s also important to remember that outdoor air isn’t always clean. In some locations, outdoor air can be contaminated by vehicle exhaust. Outdoor air can be high in ozone and high in particulates. The LBNL web site notes, “Indoor concentrations of some outdoor air pollutants can increase with ventilation rate. Increases in indoor ozone concentrations may be most significant. Higher outdoor air ozone concentrations are associated with adverse respiratory and irritation effects and several other health effects. Outdoor air polluted with ozone is normally the major source of indoor ozone. Because ozone is removed from indoor air through chemical reactions with indoor pollutants and materials, indoor ozone concentrations tend to be substantially lower than outdoor air ozone concentrations; i.e., buildings tend to shield us from outdoor ozone. However, as ventilation rates increase, indoor ozone concentrations become closer to outdoor concentrations. Thus, increasing the ventilation rates will increase our exposures to ozone.”

The same web site notes, “Increases in ventilation rates will also generally increase indoor concentrations of, and exposures to, outdoor air respirable particles, while simultaneously reducing our exposures to indoor-generated particles. Higher outdoor particle concentrations are associated with a broad range of adverse health effects. If the incoming outdoor air is filtered to remove most particles, the influence of ventilation rate on indoor particle concentrations can be small. Ventilation rates, if stable over time, will not generally affect time-average indoor concentrations of non-reactive gaseous outdoor air pollutants such as carbon monoxide, but higher ventilation rates can increase peak indoor concentrations.”

The dangers associated with outdoor ozone and respirable particles only occur in some locations. The web site notes, “It is clear that more ventilation can increase our exposures to some pollutants, particularly where and when the outdoor air is highly polluted or warm and humid. At the same time, the increases in ventilation rate will diminish our exposures to a variety of indoor-generated air pollutants. On balance, the scientific literature points to improvements in health and performance with increased ventilation rate; however, at polluted locations where it may not be possible or practical to adequately remove pollutants from incoming ventilation air, it is possible that some moderate intermediate ventilation rate is better for health than higher ventilation rates.”

According to Joseph Lstiburek, increasing a home’s ventilation rate is an unsophisticated way to address indoor pollution problems. “So what is the typical recommendation from one of these reports?” Lstiburek writes. “Increase the ventilation rate. That will reduce the concentration. Aaragghh. Dilution is not the only solution to indoor pollution. We can’t ignore the effect of ventilation rates on energy and part load humidity. We can’t just turn up the crank and ventilate like crazy. Whatever happened to source control?”

Can we determine the best ventilation rate by testing indoor air?

The idea behind mechanical ventilation is to improve the quality of indoor air. If a house doesn’t have enough ventilation, then indoor air should be bad — right? And if the ventilation system is working well, then indoor air should (presumably) be good. And there should be a simple way to test indoor air to see if it’s good or bad — right?

Unfortunately, the facts don’t conform to this simplistic view.

For one thing, the main reason that indoor air is “bad” has nothing to do with a home’s ventilation rate. It has to do with occupant behavior.

For another thing, it’s hard to test indoor air. Lstiburek notes, “I don’t have a problem with measuring CO2 — it is sometimes, not always, a pretty good surrogate for ventilation rates. … I also don’t have a problem with measuring temperature and relative humidity — I can tell a lot from measuring temperature and relative humidity. … At this point I typically stop with the testing. Why? Almost everything else is pretty much a waste of time. The most popular waste of time are tests for volatile organic compounds (VOCs).”

If you follow the link in the above paragraph, you can find out why Lstiburek believes that testing for VOCs is a waste of time. Here’s the gist of Lstiburek’s argument (with a few of my own opinions thrown in): if you want high-quality indoor air, don’t pollute the air in the first place. Don’t smoke tobacco. Don’t light candles. Don’t use plug-in air fresheners. Don’t clean indoor surfaces with solvents. Don’t spray insecticides indoors.

And if you know that there is a source of pollution in your home, install an exhaust fan close to the pollution source and use it appropriately. Taking these common-sense steps make a lot more sense than increasing your home’s ventilation rate.

Indoor air pollutants of concern

Fortunately, researchers have studied the question of which indoor air pollutants are most concerning. According to “Healthy Efficient Homes: Research to Support a Health-Based Residential Ventilation Standard,” by Brett C. Singer, Jennifer M. Logue, and Max H. Sherman, the four pollutants that are most concerning in "non-radon homes" are acrolein (a byproduct of burning tobacco, firewood, candles, and foods), PM 2.5 (fine particulate matter), NO2 (nitrogen dioxide, which is formed when natural gas is burned), and formaldehyde. The researchers conclude, “In-home air pollutant health risk dominated by PM 2.5. … Currently quantifiable chronic air pollutant health risk in non-smoking, non-radon homes driven mainly by PM 2.5.”

What’s the takeaway? If you have a supply ventilation system, the system should include a filter; and if you have a gas range, use your range hood fan. The researchers wrote, “In homes that cook with gas burners, ~50% exceed 1-h NO2, ~5% exceed CO standards.”

The bottom line

After researching existing data on the correlation between residential ventilation rates and occupant health, I have concluded that healthy-house advocates often overstate the advantages of high ventilation rates. At this point, we just don’t have enough data to make health claims for high ventilation rates. We need more research on this issue.

That doesn’t mean that we can ignore the need for mechanical ventilation in homes. I think it’s wise for builders to install equipment that allows occupants to ventilate their homes at the rate recommended by ASHRAE 62.2 (7.5 cfm per occupant plus 3 cfm for every 100 square feet of occupiable floor area). However, that doesn’t mean that every home in the U.S. needs to be ventilated at that rate.

If you care about indoor air quality, the most important thing you can do is to limit the release of pollutants — especially tobacco smoke — inside your home.

The next most important thing you can do is to employ exhaust fans for source control: for example, to remove humid air from bathrooms, to remove combustion gases from the area above your kitchen range, and to remove any noxious fumes given off by indoor hobbies.

Once these steps are taken, you’ll probably still want to operate ventilation fans — either at the ASHRAE 62.2 rate, if your lifestyle generates lots of odors or particulates, or at a rate below the ASHRAE 62.2 rate, if your lifestyle is on the non-polluting end of the spectrum.

However, these fans probably don’t need to run when no one is home, and you’ll probably want to limit use of ventilation fans during hot, humid weather.

Martin Holladay’s previous blog: “Pearls of Wisdom From Recent Conferences.”

Click here to follow Martin Holladay on Twitter.

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Mar 29, 2013 9:19 AM ET

Edited Mar 29, 2013 9:21 AM ET.

More info...Plz
by Armando Cobo

Great write-up, thank you. Your link to “Healthy Efficient Homes: Research to Support a Health-Based Residential Ventilation Standard” did not work.
A couple of questions:
1. What would be the best suggestion on ventilation strategies for homes in the Deep South with a high-humid climate, other than ERVs and a separate de-humidifier as part of the HVAC system?
2. What would be the best suggestion on ventilation strategies for homes in the middle of Downtowns, where buildings, transportation and density pollution is so much higher?

Mar 29, 2013 9:30 AM ET

In conjunction with air sealing?
by albert rooks

Thanks for the in depth look at "health & ventilation rates" based on the available facts. As we move into a period that promotes higher insulation values and lower exfiltration rates, ventilation becomes an area where we need a better understanding and practices.

During this past code cycle here in Washington State, the states (TAG) Technical Advisory Group had accepted that 3ACH50 was possible for new construction and was moving in favor of adoption. A later discussion about current ventilation practices and knowledge brought the airsealing issue to a stop. It was felt that for one to improve, the other needs to be checked and improved also.

One of the reasons I'm asking is that the home evaluation/insulation /airsealing programs seem to be gaining ground. It going to take good ventilation to keep these homes healthy. Creating tighter homes only to ventilate therm with exhaust only fans and, at times, no make up air path, seems like falling short of the goal.

In researching this subject did you come across anything that could shed light on homes that had make up air paths vs those that don't? I thinking that make up air is one significant difference between commercial and residential applications for existing buildings. Residential make up air coming from a crawl space would contain different pollutants than air through window vents (even though I think they are a silly idea).

Mar 29, 2013 9:57 AM ET

Edited Mar 29, 2013 10:20 AM ET.

Response to Armando Cobo
by Martin Holladay

Q. "Your link to ‘Healthy Efficient Homes: Research to Support a Health-Based Residential Ventilation Standard’ did not work."

A. Bummer. The link worked yesterday. Someone at the EPA evidently just pulled the document from the EPA website.

Q. "What would be the best suggestion on ventilation strategies for homes in the Deep South with a hot-humid climate, other than ERVs and a separate dehumidifier as part of the HVAC system?"

A. I recommend that every home include a mechanical ventilation system that can ventilate at the rate specified by ASHRAE 62.2. Since most southern homes include air conditioners that deliver air through ductwork, the most common type of ventilation system in the South is a central-fan-integrated supply ventilation system. It's also possible to install an HRV or ERV with dedicated ventilation ductwork.

As my article notes, during hot, humid weather, it's a good idea not to overventilate. It's up to each family to figure out what that means. In some climates -- Houston is the classic example -- you may need to install a stand-alone dehumidifier to keep indoor RH in a healthy range during the swing seasons (spring and fall).

Q. "What would be the best suggestion on ventilation strategies for homes in the middle of downtowns, where buildings, transportation and density pollution is so much higher?"

A. If the home has a supply ventilation system, make sure that the system has a filter, and check the filter regularly so that the filter can be changed or cleaned as required. If the home is near a busy intersection or highway, I would turn off the ventilation system during rush hours.

Mar 29, 2013 10:08 AM ET

Edited Mar 29, 2013 10:55 AM ET.

Response to Albert Rooks
by Martin Holladay

Q. "In researching this subject did you come across anything that could shed light on homes that had make-up air paths vs those that don't?"

A. As you probably know, there are three types of ventilation systems: exhaust-only, supply-only, and balanced systems. Your question applies to exhaust-only systems, since the other two types of ventilation systems provide ducted outdoor air.

According to the best available evidence, exhaust-only systems can work well, especially in small homes with an open floor plan. There is some evidence that the distribution of fresh air can be a problem with this type of system; however, we need far more research before we can conclude that there is anything wrong with exhaust-only systems.

There is evidence that passive air inlets are usually unnecessary with exhaust-only ventilation systems. I discuss many of these questions in my article, Designing a Good Ventilation System.

Q. "Residential make-up air coming from a crawl space would contain different pollutants than air through window vents (even though I think they are a silly idea)."

A. You make a good point. That's why builders need to have a whole-house understanding of building science principles. It's a good idea to pay attention to air sealing when designing your crawl space. A good conservative approach to crawl space conditioning uses an exhaust fan in the rim joist and a grille in the floor between the upstairs (conditioned) space and the crawl space; this approach results in crawl space depressurization. More information here: Building an Unvented Crawl Space.

Mar 29, 2013 10:15 AM ET

Edited Mar 29, 2013 10:19 AM ET.

by Armando Cobo

But here are my doubts: in a Hot-Humid climate I always spec high efficient forced-air systems with an additional de-humidifier and an ERV, but I’m always wondering if I’m highly increasing the energy usage unnecessarily, or if I just need to see it as a “must” expense; not any different than people up north who need to install 4’ of rigid foam outside the bldg enclosure or 10” under the slab. I don't think slowing outdoor fresh air is the answer... don't want a moldy or damp house. Any thoughts?

Mar 29, 2013 10:23 AM ET

Edited Mar 29, 2013 10:27 AM ET.

Response to Armando Cobo
by Martin Holladay

I believe that a responsible residential designer or builder should include ventilation equipment capable of ventilating a home at the rate specified by ASHRAE 62.2.

Once the home is completed, however, it's up to the homeowner to decide how to operate the equipment. You can provide advice, but you can't control how they operate their fans.

Some families have lifestyles that don't require a lot of ventilation. Other families have lifestyles that require more ventilation.

We are all awaiting more research on these issues, Armando.

Mar 29, 2013 10:53 AM ET

by Armando Cobo

Good points, I guess I'll sleep good from now on...

Mar 29, 2013 11:17 AM ET

Free information
by Armando Cobo

There is a bunch of free information from the EPA in PDF format at air cleaning devices

Mar 29, 2013 11:42 AM ET

Response to Armando Cobo
by Martin Holladay

Thanks for providing that link. Here is the bottom line, according to the EPA:

"The best way to address this risk [the risk of indoor air pollution] is to control or eliminate the sources of pollutants, and to ventilate a home with clean outdoor air. The ventilation method may, however, be limited by weather conditions or undesirable levels of contaminants in outdoor air. If these measures are insufficient, an air cleaning device may be useful. While air cleaning devices may help to control the levels of airborne allergens, particles, or, in some cases, gaseous pollutants in a home, they may not decrease adverse health effects from indoor air pollutants."

Mar 29, 2013 8:30 PM ET

Ventilation rates and health
by Don Fugler


It is an elusive relation: does better indoor air quality lead to improved health? There have been many studies of indoor air quality and ventilation rates. Most show that higher rates, within reason, reduce indoor air pollutants and should lead to better IAQ. There have been some attempts at making a better correlation between good IAQ and occupant health. There was some work in Canada's far north where most infants have terrible bouts of respiratory illness. Despite the problems of doing research in the north, and a relatively small sample, there were some encouraging results at: Another excellent project was looking at the ventilation rates, IAQ, and respiratory health of over 100 asthmatic children in Quebec City. Again, more ventilation led to improved IAQ but the medical improvements were more nebulous. This study is still being published here and there but here are references to some of the papers:

It has been difficult to find the best number to insert into standards such as CSA F326 and ASHRAE 62.2. I think the research has shown that air exchange rates (including mechanical ventilation) in the order of 0.3 ACPH for many houses (or 30-60 L/s) result in most indoor pollutants being reduced below guideline levels. This seems like a reasonable goal until we get the expensive health research completed.

Mar 30, 2013 5:50 AM ET

Response to Don Fugler
by Martin Holladay

Thanks for providing the two links. The abstract of the Inuit study reports that "Use of HRV, compared with placebo, was associated with a progressive fall in the odds ratio for reported wheeze of 12.3% per week ... Rates of reported rhinitis were significantly lower in the HRV group than the placebo group in month 1 ... and in month 4 .... There were no significant reductions in the number of health center encounters."

My girlfriend, Dr. Karyn Patno, is a pediatrician who worked for years in a Yup'ik community (Bethel, Alaska). She has told me about the frequent respiratory problems of Yup'ik children, which sound similar to the symptoms reported in Inuit communities. The study you linked to shows significant results, although it is unclear whether the findings are broadly applicable in other cultural settings or other climates.

It sounds like the Quebec City study is ongoing, and I was unable to find a paper reporting any medical data. I'll take your word for it that "the medical improvements were more nebulous."

I agree that 0.3 air changes per hour -- a ventilation rate that is close to the standard that has been floating around for 24 years (ASHRAE 62-1989) -- "seems like a reasonable goal until we get the expensive health research completed."

Mar 30, 2013 10:07 AM ET

Passive heat recovery system
by Scott Simpson

A very clever passive heat recovery unit has just come onto the market called Ventive here in the UK - which means, unlike MVHR, zero electrical input and no noise. And a lot less space. Too early to have any feedback from installations but it sounds genius - especially with the move to air-tight Passivhaus standards and keeping embodied carbon low. Not sure about costs, but you can find info about them here:

If anyone knows of any other passive heat recovery system - or research papers - I'd be grateful to hear about it.

Mar 30, 2013 12:57 PM ET

Edited Mar 30, 2013 1:01 PM ET.

Sick building syndrome study telling, but...
by Skip Harris

Joe L's assertions about studies only showing issues with industrial pollutants, not residences or office buildings, seems contradicted by the SBS study showing an inverse relationship between ventilation rates and SBS in office buildings. It seems that if one could put a price on SBS and on ventilation, one could then easily calculate the most cost-effective rate of ventilation.
Of course, studying buildings with low-ventilation and low SBS rates might be informative as well.

Mar 31, 2013 8:34 AM ET

Edited Mar 31, 2013 12:02 PM ET.

Response to Dustin Harris
by Martin Holladay

I won't presume to speak for Joseph Lstiburek, who may well agree with you.

However, I can think of several ways in which office buildings differ from homes:

1. Most office buildings have more people per square foot than most U.S. homes.

2. Most office buildings have equipment (for example, copy machines) that isn't found in most U.S. homes.

3. Many (perhaps most) U.S. homes are empty during the day and occupied at night -- the opposite pattern from most offices.

4. The cleaning products used in offices may differ from the cleaning products used in homes.

We need more research on these issues.

Mar 31, 2013 7:17 PM ET

Joe would be proud of me; I'm
by Hobbit _

Joe would be proud of me; I'm ventilating at an average of
about 0.1 ACH in a volume of 15,000 cubic feet. [This also
answers the question over in the "Maine" thread.] That's the
lowest the Fantech will run, and keeps the CO2 at a more than
adequate 700-800 ppm. I've shut down the ventilation on a
few occasions just to see how quickly my own "miasma" builds
up; it takes almost 24 hours before it's at what we'd
consider unhealthy levels, and opening a couple of windows
or going to high-ventilation zaps it right back down. No
appreciable rise in humidity just from respiration.

So I've got a fairly decent handle on how much ventilation
is needed for my own situation. I agree that monitoring CO2
is a convenient indicator, as well as humidity in places
where it tends to accumulate faster, and I'd love to hear
of more building maintainers routinely watching that stuff.

I wouldn't want to run ventilation in hot humid weather unless
that air is being actively dealt with -- whole-house dehum, a
heat-pipe setup, or sent into the main air-conditioning system
when we're *certain* that it's running. That's why I threw
together that "HRV integration" stuff for the HVAC -- that's
for summmer, and if there are times when no actual cooling is
needed but the outdoor air is yuckier than I could possibly
cause my indoor air to be, the HRV will remain inactive.


Apr 1, 2013 2:32 AM ET

Cats & Dogs, HEPA Filters, Sinusitus, Measuring Air Changes
by Kevin Dickson, MSME

It's becoming obvious that trying to correlate a minimum residential ventilation rate with health is impossible.

Just a few additional complications worth mentioning:

1. You can't measure the natural infiltration rate of any house accurately. Therefore all the homes in a study would have to be tight enough to make the natural ventilation negligible compared to the forced ventilation. Since you would have trouble guaranteeing that all the windows and doors are closed all the time, this is impractical. Even a tracer gas test would be meaningless because of variable outdoor conditions and house geometry. Food for thought:

2. "Health" is relative. Dr. Rebecca Bascom, in her comments on the ASHRAE 62.2P, said, "health varies wildly among people; and susceptibility to health problems varies widely." Maybe you could identify an minimum ventilation rate for sinusitis, but that would be different than asthma.

3. Some studies may indicate that dirty kids (breathing dirty air) may be healthier adults, quoting from the internet: "One study of Amish children who live and work on farms, published in the Journal of Allergy and Clinical Immunology, suggested that early-life exposure to allergens may prevent the immune system from developing allergies." Allergists inject you with the allergen in an attempt to cure your allergy. Isolating yourself from allergens by having clean air could make your allergies worse.

4. Is re- filtering indoor air with a HEPA filter worth doing?

5. If you actually comply with ASHRAE 62.2, even using an ERV, your indoor air can be uncomfortably dry during very cold weather. Bumping the humidity back up to 35% with a humidifier will cause condensation and mold on most double pane windows. High performance windows will solve this one.

6. House pets can cause health problems that ventilation can't prevent.

7. Maybe healthy air can be manufactured from stale air with an oxygen concentrator and an ion generator?

Apr 1, 2013 10:29 AM ET

Response to Kevin Dickson
by Martin Holladay

Thanks for your perceptive comments.

Concerning point #2 -- "Health" is relative: Public health researchers are familiar with the study of correlations between a variety of factors and human health. Some factors -- like tobacco smoking or lack of exercise -- show a very strong correlation with health outcomes. These correlations jump right out when you look at the data.

Residential ventilation rates don't fall into the same category, it seems to me. If there is a correlation between residential ventilation rates and occupant health, the correlation is likely to be very weak.

Apr 3, 2013 12:18 PM ET

NESEA workshop
by Dan Kolbert

I haven't checked to see if NESEA has posted workshops from BE13, but Lew Harriman and Bill Rose gave a great one called "Should Code Regulate Humidity & Moisture in Buildings." Good disagreements on their parts on what and how, but they both agreed that the metrics currently available and in use are inadequate. If the presentation isn't up, I can try to put my notes into some kind of presentable shape.

Apr 3, 2013 12:33 PM ET

Response to Dan Kolbert
by Martin Holladay

I found the link: Should Building Codes Regulate Humidity and Moisture in Buildings?

Apr 3, 2013 12:40 PM ET

Edited Apr 3, 2013 12:41 PM ET.

Some quotes from Lew Harriman and Bill Rose's presentation
by Martin Holladay

Here are some quotes.

Bill Rose: "Perceptions of dampness have been shown to be associated with increased risks to public health and safety. [But] Quantified dampness has not been shown to increase risks to public health and safety."

Bill Rose: "What prompted the initial incursions of regulation (building codes) into moisture control? How successful has that been? (I would argue not successful. Moisture control is as contentious now as it has ever been.)"

Bill Rose: "What is the three-way link between dampness, health and ventilation?" [Editor's note: Bill does not answer the question, at least not in the presentation slides.]

Lew Harriman: "We don’t know the dose-response relationship between moisture, mold, microbial growth and health, BUT...we DO KNOW that damp buildings are not healthy. So I don’t think continuing to ignore the issue in codes (because it’s difficult and problematic) serves the public interest."

Apr 3, 2013 4:50 PM ET

Ventilation is not about supplying anything
by Max Sherman

Great blog. A few comments:

• Correction: Acrolein is generated by combustion of almost any carbon-based fuel—cooking, candles, etc. It is not just a tobacco issue.

• Correction: The total ventilation in 62.2 is 3 cfm/100 sq.ft. plus 7.5 cfm/p not 1 cfm/100 sq. ft. In the 2010 version there was a built-in infiltration credit of 2 cfm/100 sq. ft. to get the number you quoted for mechanical systems. In the current version, however, that default infiltration credit is gone. You can, however, get an infiltration credit based on a blower-door measurement.

• Joe and I agree on almost as many things as we disagree on… it’s just that the disagreements are more entertaining for other people.

• Joe and I agree that ventilation is an important factor in getting IAQ, but not the only one. Clearly the emission rate of contaminants of concern are also important. We need to improve the science of all of this and not just do correlations with ventilation rates and say we learned something.

• Ventilation is not about supplying fresh air — it is not about supplying anything. The only things people “use up” in air is the oxygen and something like 2% of the 62.2 ventilation rate would be enough to supply that. Ventilation is principally about removing indoor-generated contaminants of concern. The more you can capture them at their source and the less you can distribute them to the occupants, the better it is.

• Current ventilation standards are set based on engineering judgment by a room full of “experts”, but some of us would like to see that transition to be based on a bit more causality and science. That is the direction my research has gone in the last few years. You might be interested in a recent interview I did: Moving Toward a Health-Based Ventilation Standard.

Apr 3, 2013 4:54 PM ET

Response to Max Sherman
by Martin Holladay

Thanks very much for your comments. I have made your suggested corrections; I appreciate the information very much.

And thanks for the link to the interview, "Moving Toward a Health-Based Ventilation Standard." It's a valuable document.

Apr 3, 2013 6:39 PM ET

Health correlations, houses, specificity
by Derek Roff

As Kevin mentioned, it is very hard to do good research on health outcomes of people living their everyday lives. There are too many variables. Drawing good statistical conclusions on the impact of residential indoor air quality on an aspect of health requires tracking continuously the indoor air quality of many different homes, along with tracking all the other things the residents do outside their homes, and what kind of air they are exposed to. Giant sample sizes are needed. Data collection and correlation of all those factors is overwhelming.

Martin points out that we have data on the health impact of smoking, or of lack of exercise. Indeed, we have data on various single variable questions. I bet we don't have data on the impact of the residential ventilation rates on smoking's health hazards. Adding additional variables increases the cost of good research exponentially.

In the absence of comprehensive data to answer complex questions on indoor air quality, we can either give up, or look for other ways to make useful choices. I like Don Fugler's answer. We know a good bit from laboratory and other tests about the health risks to mammals of breathing a number of chemicals, including several common indoor air pollutants. While we don't have data proving that breathing a varied mixture of these pollutants in a home is also unhealthy, that's the way that I'm going to bet. Minimizing the introduction or production of these pollutants within the home, and ventilating to reduce those that are found to be in present in a given house, seems like a prudent strategy.

It is encouraging that both Don's study of Canadian and other research, and Martin's reference to the 24-year old ASHRAE 62-1989 proposal, suggest a minimum of 0.3 air changes per hour.

Apr 3, 2013 7:51 PM ET

0.3 ACPH
by Don Fugler

Just a qualification on this number: while a number of research projects show that a house air change rate of 0.3 is reasonable at keeping high levels of indoor pollutants at bay, this is for typical houses with typical occupation. A 7000 square foot house with a single resident probably needs no mechanical ventilation other than a bathroom fan. A small house with an active family of six might require 1 ACPH of continuous mechanical ventilation. Houses with high pollutant sources will need higher ventilation rates (or source reduction).

Apr 4, 2013 4:59 AM ET

Response to Derek Roff
by Martin Holladay

Thanks for your comments; I agree with most of what you have written.

You wrote, "Martin points out that we have data on the health impact of smoking, or of lack of exercise. Indeed, we have data on various single variable questions. I bet we don't have data on the impact of the residential ventilation rates on smoking's health hazards. Adding additional variables increases the cost of good research exponentially."

I understand your point, but I'm not suggesting that we complicate the research by introducing two variables. (We do have data on the health effects of two variables, by the way -- exposure to asbestos and smoking spring to mind.) Let's stick with a single variable -- the ventilation rate provided by installed ventilation fans -- and see what we come up with. We have large longitudinal studies -- the most well-known is the Framingham study -- that look at variables like this. The research is expensive but not particularly complicated.

Preliminary attempts to look at a correlation between residential ventilation rates and occupant health have not yet come up with a strong correlation.

You wrote, "I like Don Fugler's answer." Don Fugler's suggestion -- "0.3 ACPH ... seems like a reasonable goal until we get the expensive health research completed" -- is very similar to the suggestion I made: "it’s wise for builders to install equipment that allows occupants to ventilate their homes at the rate recommended by ASHRAE 62.2."

Apr 4, 2013 5:03 AM ET

Second response to Don Fugler
by Martin Holladay

Thanks for your comment on the need to use common sense when deciding on a ventilation rate. I agree with you completely -- some homes should probably be ventilated at a rate that is less than 0.3 ach, while others should probably be ventilated at a higher rate.

Once again, we're back to the usual answer to so many questions we face: "It depends."

Apr 4, 2013 9:07 AM ET

Air change
by Roger Anthony

Surely it is illogical to base ventilation on the volume of a building.

Logic says if a person is breathing 7 litres of air a minute, lets replace 7 litres a minute.
If there are more people, then provide more air.

What are people doing in their homes? Usually sitting, occasionally doing household chores.

These activities use about 7 litres of air a minute.We should multiply this by the number of people
in the home at the time.

A minimal amount of air change at minimal cost.

If pollution or high humidity is introduced then
open a window.

Apr 4, 2013 4:17 PM ET

Air changes
by Roger Williams

I have played with our air exchanger, using a highly scientific approach. I reduced the air changes until my wife complained, then went a little above that level. She has athsma and needs fresh air to be comfortable. According to the ratings of our HRV we are replacing the air at .2 ACH in normal conditions and raise that to .8 ACH during a family dinner/gathering. Seems to work well for us.

Apr 4, 2013 10:17 PM ET

Plants and IAQ
by Mike Nelson Pedde

While not specifically related to ventilation, this talk on improving IAQ might be of interest:


Apr 5, 2013 6:40 AM ET

HEPA Filters
by Kevin Dickson, MSME

Max Sherman's paper indicates that yes, it would be very beneficial to recirculate the indoor air through a filter to remove P(2.5) particulates. Those particulates are apparently the worst of all the indoor pollutants.

You can remove them without fresh air and its resultant energy penalty.

Another house-caused source of respiratory health problems is Legionella. If the hot water tank is kept at, say, 105F and used for showers, it could cause bacterial pneumonia. European codes already address the problem. Ventilation wouldn't help on that one.

Apr 5, 2013 7:47 AM ET

Response to Mike Nelson Pedde
by Martin Holladay

Kamal Meattle's suggestions make sense in New Delhi, where he can hire low-wage custodial help to hand-wipe the leaves of the plants he installs in office buildings. His program is unlikely to be adopted by busy American families. He suggests installing three species of plants in your home. One of them is the areca palm.

He says, "Areca palm is a plant which removes CO2 and converts it into oxygen. You need 4 shoulder-high plants per person, and in terms of plant care, you need to wipe the leaves every day in Delhi, and perhaps once a week in cleaner air cities. We need to grow them in vermi-manure which is sterile, or hydroponics. And take them outdoors every 3 to 4 months."

OK, that makes sense. If there are four people in my family, I need 16 shoulder-high plants in my living room. And every day, when I come home from work, I will wipe all of the leaves (because I don't have a maid who works for a few rupees a day). And how am I going to put them outside in Vermont in December and January?

Oh, I forgot to list the other requirements -- you need room for lots more plants in your bedroom and the other rooms of your house as well...

Apr 5, 2013 7:21 PM ET

Edited Apr 5, 2013 10:07 PM ET.

Mechanically Tightened Shell + Fresh Air Intake
by Steven L

Martin, and everyone posting to this website, I find all of your discussions both enlightening and a bit overwhelming. I feel that I'm learning so much, but also that I have so much to learn. I would like to solicit some opinions if possible.

My wife and I are designing and building a new home in the Texas Hill Country (west of Austin). I was discussing HVAC / Insulation / Air Exchanges with them and they are suggesting a "Mechanically Tightened Shell with Fresh Air Intake." This seems to consist of construction cement, or some adhesive, added to the stud face, bottom plate, and top plate along exterior sheathing and drywall joints. No mention of outlets. As for the Air Intake, I am assuming it to associated with the HVAC system.

The price is $4,500 for a ~3,000 sf house [3 bedrooms, 1 office (only room upstairs), 2 1/2 baths - propane fireplace - standing seam metal roof - rock exterior ~5" thick, long southern porch for shade].

I had really wanted to go with foam, but it appears this is not going to be possible and they are proposing blown in insulation. I would really like to hear any comments you might have on this approach.

Thank you in advance,

Apr 6, 2013 6:06 AM ET

Response to Steven L
by Martin Holladay

If you care about airtightness -- and you should -- the best way to verify the airtightness of your home's envelope is with a blower door. I hope that your builder performs a blower-door test on your house. Ideally, you should have a specification that includes an airtightness goal. (However, it may be too late for that in the case of your current project.)

Here is more information on blower door testing: Blower Door Basics.

I'm not sure what your builder means by "construction cement, or some adhesive, added to the stud face, bottom plate, and top plate along exterior sheathing and drywall joints" -- but I'm guessing that this is a reference to either Owens Corning EnergyComplete and Knauf EcoSeal. For more information on these products, see Air Sealing With Sprayable Caulk.

The reference to an "air intake" may refer to a central-fan-integrated supply ventilation system, but there is no way of knowing what the builder has in mind unless you ask. For more information on central-fan-integrated supply ventilation systems, see Designing a Good Ventilation System.

Apr 6, 2013 10:14 AM ET

Edited Apr 6, 2013 10:56 AM ET.

Response to Martin Holladay Re: Mechanically Tightened Shell...
by Steven L

Martin - Thank you so much for the quick response, as we are driving down to meet with the builder on Monday. The information that you provided and pointed to will be of great assistance at that meeting. I am reading, digesting, and taking notes now.

FYI... we have changed builders mid-stream (long story) and I am now having to adapt to and understand how the the new guy thinks.

The original design called for the attic to be within the conditioned space because we were using foam - allowing smaller than normal A/C equipment (two stage) and providing nice attic storage. We also want to use can lights so this was a good solution.

As I mentioned in the earlier post we seem to be switching to blown-in insulation, but I would like to continue using two stage A/C and can lights. But, from what I read here without keeping the attic within the conditioned space this is problematic without sealing the cans with drywall top-hats (or Seal-a-Lights which don't seem air-tight) and increasing the A/C size. Can I economically keep the attic in the conditioned space without foam? Is there a trade-off or solution that someone here can suggest?

Thanks Again,

Apr 6, 2013 1:16 PM ET

Edited Apr 6, 2013 5:11 PM ET.

objective of better air quality
by Morris Charney

When I first read "Musings of an Energy Nerd" I was rather put off by the underlying message of the article but I must say I am rather impressed by all the informed responses it generated. Allow me to explain my initial negative reaction because I think Martin Holladay needs to reconsider some of his comments.I am an architect who has been practicing for 50 years with an emphasis on building inspections. Doing building inspections gives you the chance to see trends as they develop in buildings without having to wait for definitive research which summarizes so many of the responses this article has generated. Those of us who experienced the altruism of the 60's , the Energy Crisis of 1973 and all the Building Code changes that followed to conserve enegy in buildings hopefully learned something that is not so evident even with all the information now available over the internet. Martin's article is full of interesting anecdotes but an argument can be made today for most any hypothesis given the facility of references from the internet. A good building design should have multiple objectives. I contend that the objective of conserving energy is no more important than the objective of creating a healthy environment and in that regard, the first seems to be progressing at the expense of the second and that is not a good thing. Many of the derogatory remarks at the start of the article are typical. I still believe that homes with plenty of fresh air are inherantly heathier than homes that are stuffy and do not have adequate air changes. It is still valid today and more necessary than ever. The connection between ventilation and human health was championed in sanitoriums [rather than by 'sanitarians' as Martin suggests]. Mentally ill people were housed in asylums whose original definition was a place of sanctuary. Now a-days it is estimated that three-fourths of mentally ill Americans are in jails or pententiaries.Canadian Medicare as articulated in the 1984 Canada Health Act had wonderfull objectives which Canadiand can all be proud of--part of our heritage. When the National Buildig Code was changed in 1995 in response to the fact [as explained in the annex of that year] that interior air pollution was seriously defective, we could no longer rely on natural ventilation [opening windows] to achieve a healty environment, and that air changes [fresh air/oxygen] had to be delivered to each and every inhabited room[at a rate similar to ASHRAE's standard complete air change in about 3 hours--it was a wonderful accomplishment. Here we are in 2013 and it isn't happening. Martin muses as to its importance. All these responses from academics and scientists waiting for definitive research to be done on the subject Many are still suggesting opening windows. The uri-formaldehyde trial was the longest running civil case in Canadian history and ended with an indecisive judgement because not enough difinitive research had been done correlating it to health issues. Try doing some building inspections in urban areas not out in the Vermont countryside [installing solar panels to conserve energy] to get a better sense of how compelling the problem of air quality has become.In Montreal,for example, we have nurseries and primary schools that are so unhealty [bad air quality, mould infestationsd] that many have been boarded up and supposedly they are to be demolished and rebuilt. Most of that has to do with the lack of maintenance and poor initial mechanical designs.There is hardly any mechanical code enforcement even in new construction [especially renovations of older buidings] in regard to vital mechanical aspects such as providing fresh air /oxygen and sufficient air changes. I met one builder/contractor at an inspection who told me of renovating 70 older homes in the fashionable Plateau Mt-Royal area and all of them depended on opening windows for "natural ventillation". The other day I inspected a luxurios condominium in Vieux Montreal selling for 1.5 million having gone through a $350,000 renovation yet the mechanical didn't work [made a lot of noise but it did not involve fresh air or air changes]. It faced due south and the vendor said he preferred opening windows. That's a crock. Do building inspections and you will see how no one opens a window when it is too cold, rainy or too hot and humid outside. That's why the building code was changed in the first place. When you get CO2 readings over 1000 ppm and climbing and outside it is 350ppm, you know that can't be healthy. Meanwhile I got carbon monoxide readings in the common areas including the swimming pool , the gym/work-out centre and the garage.We shouln't be waiting for more research, more proof [like the global warming issue or climate change]. You just have to use common sense and observe. To this day, the first thing checked when you go to the hospital is the oxygen content of your blood. It is done for a purpose.

Apr 7, 2013 6:16 AM ET

Edited Apr 7, 2013 7:17 AM ET.

Response to Morris Charney
by Martin Holladay

This article does not question the need for mechanical ventilation in homes. It is about ventilation rates, not about whether ventilation is necessary.

I have championed the need for residential ventilation for many years. This article includes a link to my 2009 article, Designing a Good Ventilation System, in which I wrote, "Homes without ventilation systems are homes of the past. The building science community has reached a consensus: build tight and ventilate right." In the article on this page, I once again emphasize this important point: "It’s wise for builders to install equipment that allows occupants to ventilate their homes at the rate recommended by ASHRAE 62.2."

This article looks at the existing scientific evidence linking residential ventilation rates with human health. It's hard to go forward to make recommendations to builders and homeowners if we don't first start with an examination of the scientific evidence.

You wrote, "An argument can be made today for most any hypothesis given the facility of references from the internet." That may be true, but in my research I didn't rely on just any old references on random web pages. I relied on interviews with Max Sherman, a senior researcher at Lawrence Berkeley National Laboratory, a nationally recognized expert on residential ventilation who has performed years of research on the topic and who is the former chair of the committee that developed the ASHRAE 62.2 standard. (I have been interviewing Max Sherman on this topic for at least 12 years, since I was editor of Energy Design Update. By the way, I happen to feel a certain kinship with Max, since he has received an ASHRAE award named after my grandparents: the Louise and Bill Holladay Distinguished Fellow Award.)

I also relied on the best published research I could find on the topic, and on interviews with Joe Lstiburek, another former member of the committee that developed the ASHRAE 62.2 standard.

You wrote, "The connection between ventilation and human health was championed in sanitoriums [rather than by 'sanitarians' as Martin suggests]." I know the difference between a sanitorium and a sanitarian, Morris. A sanatorium is a type of health facility, while a sanitarian is a public health expert. The term "sanitarian" was in use over a hundred years ago, when public health issues in urban tenements and "miasma" fears were national concerns; the term is still in use today.

You wrote, "When the National Building Code was changed in 1995 in response to the fact [as explained in the annex of that year] that interior air pollution was seriously defective, we could no longer rely on natural ventilation [opening windows] to achieve a healthy environment, and that air changes [fresh air/oxygen] had to be delivered to each and every inhabited room[at a rate similar to ASHRAE's standard complete air change in about 3 hours--it was a wonderful accomplishment." I agree, and nothing in my article disputes the wonderfulness of that accomplishment.

You wrote, "Try doing some building inspections in urban areas not out in the Vermont countryside [installing solar panels to conserve energy] to get a better sense of how compelling the problem of air quality has become." In fact, for seven years in the 1990s, I worked as an inspector doing capital needs assessments for low-income housing projects, many of which were located in Burlington, Vermont -- not that far from Montreal. I visited countless occupied homes and apartments. I have seen it all: moldy bathrooms, dripping windows, plumbing leaks under kitchen sinks, wet crawl spaces, and attics filled with mold. I have seen non-functional HRVs, disabled bath fans, and confused occupants.

Like you, I have a strong desire to make good recommendations to designers, builders and homeowners facing this type of problem. That takes a whole-house approach based on building science. We can't address these issues without a foundation in scientific knowledge based on data. This article is an attempt to look at the existing data so that we can all go forward with sound recommendations.

Apr 7, 2013 5:49 PM ET

I must say your answer to my
by Morris Charney

I must say your answer to my comments is very different from what I understood of your "musings of an energy nerd". If it was meant to be about ventilation rates and not about the need to ventilate [mechanically] then why is it that so many follow up responses seemed to be questioning the need for mechanical ventilation and alluding to the benefits of opening windows [natural ventilation]? My point was that mechanical ventilation requirements as expressed in the 1995 code are not being followed and are being reduced significantly by those promoting conservation of energy. Manufacturers have come up with air exchangers/heat recovery ventilators which don't work. They are not operated continuously, they pollute too easily because filters are too rudimentary, the air volumes are too restrictive, incapable of achieving a complete air change within 3 or 4 hours and most use flexible ducts which can't be cleaned. The preoccupation with outside pollutants [fresh air being the source of the oxygen that is needed] is also a non-issue if one uses a filter of Merv 11 quality [4 inch, pleated ,disposable]. Noone seems to be willing to promote good air quality [as prescribed in the code] with the excuse that it can only be accomplished at the expense of energy conservation objectives. Why would the rate even be an issue [which you say was the essence of your article] when variable speed controlls are available for mechanical equipment. Most AE/HRV units currently in use are being operated with humidistats [which makes no sense]. HVAC systems, AE/HRV's and their controls are needlessly complicated. When the air changes are adequate in a home, you are able to smell the fresh air, you know that it is working. Why suggest that we can't address questions [such as the rate of mechanical air changes] "without a foundation in scientific knowledge based on data". The judgement that came out of the urea-formaldehyde case was to the effect that the degrees of sensitivity varied by individual and you can't make generalized correlations between contaminants and individual health based on absolute numbers. That is why we do not have fixed standards for mould spores, bacteria or most other airborn microscopic contaminants for indoor air. Indoor air is compared to outside air [supposed to be better]. We are finally starting to accept that HES people all have different levels of sensitivity to electromagnetic fields. It would be similar in regard to airborne contaminants. I am suggesting that the rate is not an issue if you provide an HVAC system including a fresh air intake with a variable speed. It isn't happening because homeowners [when they have a choice] are being told it would cost too conserve energy.

Apr 8, 2013 4:16 AM ET

Edited Apr 8, 2013 8:58 AM ET.

Response to Morris Charney
by Martin Holladay

I suspect that you and I are in agreement about many issues relating to residential ventilation. I think you are reacting to guesses concerning what I have written rather than to the words I wrote. I urge you to read carefully what I have actually written.

You sound frustrated that many residential ventilation systems are poorly designed, poorly installed, and operated incorrectly. These issues frustrate me as well, which is why I wrote, "Several research studies have shown that a high number of mechanical ventilation systems are poorly designed or installed. Among the common problems: Ventilation fans with low airflow because of ducts that are undersized, crimped, convoluted, or excessively long."

You wrote, "If it was meant to be about ventilation rates and not about the need to ventilate [mechanically] then why is it that so many follow up responses seemed to be questioning the need for mechanical ventilation?" Well, Morris, I'm not sure -- but this website is a lively forum that attracts opinionated readers who like to debate, and the give-and-take by readers often results in a spirited dialogue. I can hardly be faulted for the opinions of people who post comments on these pages.

You wrote, "My point was that mechanical ventilation requirements as expressed in the 1995 code are not being followed." The problem of code compliance is not restricted to Canada. We also have a huge code compliance problem in the U.S. The issue is complicated, but I am on your side on the issue of code compliance, which I address frequently on these pages. For example, I have written, "Several studies have documented the fact that in many areas of the country, energy code provisions [are] largely unenforced. ... To this day, most Vermont jurisdictions have no building inspectors. In essence, the Vermont energy code is entirely voluntary. ... The trouble with uneven enforcement, however — in addition to the obvious point that energy waste contributes to global climate change — is that a builder can never be sure when a new building official will begin enforcing long-ignored regulations."

You are frustrated that many homeowners have ventilation systems that "are not operated continuously." This will be a tough problem to solve. I'm not exactly sure how you are going to enforce regulations requiring homeowners to operate their ventilation equipment according to your preferences rather than the homeowners' preferences. I think the best we can hope for is that -- at a minimum -- builders install equipment capable of ventilating at the rate recommended by ASHRAE 62.2.

You wrote, "HVAC systems, AE/HRV's and their controls are needlessly complicated." I share your frustration with overly complicated HVAC equipment, which is why I wrote (In Simplicity versus Complexity), "Many of today’s harried homeowners don’t even know where all of their mechanical equipment is located, much less the equipments’ maintenance requirements. ... When specifying equipment, keep it simple."

You ask, "Why suggest that we can't address questions [such as the rate of mechanical air changes] without a foundation in scientific knowledge based on data?" My conclusion in this article is the same as yours: although we lack enough data to pin down a correlation between ventilation rates and health, we nevertheless should provide and use mechanical ventilation systems. Even though there are gaps in our knowledge, and even though research is spotty, we need to go forward with the best information we have. That said, it's always a good idea to look at the data we have.

I certainly agree with another one of your points: "The judgment that came out of the urea-formaldehyde case was to the effect that the degrees of sensitivity varied by individual and you can't make generalized correlations between contaminants and individual health based on absolute numbers." That's one of the obvious conclusions of the article on this page; that when it comes to making recommendations on the ideal ventilation rate for homes, the best answer is often, "It depends."

In short, Morris, you have set up a straw man and argued strongly against him. I am not that man.

Apr 9, 2013 9:20 AM ET

A blog by Matt Risinger
by Martin Holladay

A recent blog by Matt Risinger (posted on the Fine Homebuilding website) picks up some of the same themes discussed here.

Dec 17, 2013 7:21 PM ET

Thanks for a Great Post on Ventilation
by John Krigger

As usual, you do your literature research and present a large amount of information in a small space very efficiently. You are a terrific writer too. Keep up the good work!

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