Homeowners don't always know what's best for them. This is especially true where ventilation is concerned. Basically, most homeowners cannot determine whether or not the minimum ventilation rates are being met. For this reason, ASHRAE Standard 62.2 states that mechanical ventilation is preferable to windows or other systems that require occupant control or provide unpredictable amounts of ventilation.

The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) published Standard 62.2, "Ventilation and Acceptable Indoor Air Quality in Low-rise Residential Buildings," in December 2003.

American National Standards Institute (ANSI) approved the standard in early 2004, which means that many code bodies may soon be looking to incorporate all or part of the standard in local codes.

The standard is not without controversy. It was published over objections from home builder and appliance manufacturer groups. These groups questioned whether specific links could be made between ventilation rates and health risks, as well as whether the standard would limit certain types of equipment. (Several industry groups have filed an appeal with ANSI, and a hearing is set for August 2004.) The ASHRAE committee responsible for drafting the standard, however, feels confident that it will provide solid information to the industry concerning all aspects of residential ventilation.

Controlling At The Source

Before 1996, the only way ASHRAE standards addressed residential ventilation was as a small part of its broader ventilation standard, Standard 62. In 1996, ASHRAE recognized that there was a need to have a separate standard for residential ventilation and formed a committee to do just that. Seven years later, ASHRAE approved Standard 62.2-2003.

Standard 62.2 is not an overly complex or long document, and it is applicable to both new and existing homes, including all single-family homes and small multifamily ones. As a standard intended for use in regulation, 62.2 describes the minimum requirements necessary to provide acceptable indoor air quality for typical situations. The standard is basically a trade-off between dilution ventilation and source control.

"In a sense, ventilation is the method of last resort for controlling indoor air quality," said Max Sherman, Ph.D., senior scientist, group leader, Lawrence Berkeley National Laboratory, Berkeley, Calif., and former chairman of Standard 62.2. "The most important thing to do is focus on the sources of contaminants. See if you can control them so you don't have to ventilate excessively. This is one reason why there's no magic ventilation rate, because it depends on those sources."

Sherman noted that the problem with indoor air quality is that it's tough to pin down exact causes and effects. Poor indoor air quality can lead to acute symptoms, but more often than not problems lead to chronic issues. "However, there is a large body of research that shows that contaminants affect people's health, and ventilation and source control reduce contaminant concentrations," he said.

While the ventilation rates really depend on the sources of contaminants in the home, the committee came up with a whole-house mechanical rate, which is 1 cfm per 100 square feet, plus 7.5 cfm per person. The typical range is between 30 and 80 cfm.

The kitchen is usually a major source of contaminants in a home, as the cooking process generates many particulates and chemicals. For this reason, the 62.2 committee mandated kitchen exhaust in the standard.

Said Sherman, "The kitchen requirement was a controversial requirement, because builders didn't want to have to put in a fan that exhausted outside in every kitchen. They wanted to say the windows were good enough. The committee decided that couldn't work."

The committee also decided to include a sound requirement for fans. The committee's position was that noisy fans are a barrier to their operation, and if they're not operated, they won't do what they're supposed to do. The builders contested this issue as well, claiming that a ventilation standard should not address noise issues.


Some argue that including mechanical ventilation will price some homeowners out of the market, as it will add $6,000 to $8,000 for a house built to Standard 62.2 recommendations. Of course, that number depends greatly on the design of the house. If a house is poorly designed from the point of view of residential ventilation, then it might cost thousands of dollars to add this feature. An example of this is if a kitchen is designed such that there is no way to run a duct from the stove to the outside. It would cost quite a bit to put in a duct for the exhaust fan.

"On the other hand, people are doing this kind of thing right now and they're saying it costs about $200, because they've thought through the design ahead of time," said Sherman. "We know it can be done cheaply because people are already doing it cheaply."

Fortunately, it's becoming even less expensive to include mechanical ventilation because there are more products available.

When the standard first went out for public review in 1999, the committee decided to hold off requiring quieter kitchen fans because there weren't any available. Now there are plenty of products available that meet the standard for ventilation and sound control (many can be viewed at the Home Ventilating Institute, www.hvi.org).

The type of ventilation needed may also vary by climate. In a cold climate, excessive supply ventilation may push moisture into the walls, causing problems. In a humid climate, excessive exhaust ventilation may pull the hot humid outdoor air into the walls, causing rot. The committee spent a lot of time examining these issues, and they did come up with a limit, stating if a certain amount of ventilation is exceeded, special precautions have to be taken.

"That limit is above what the standard requires, so if you're just building to the minimum, the standard does not require you to do anything special," noted Sherman. "The typical 50 cfm, by itself, is not going to cause walls to rot no matter what you do, because if you look at a house with no ventilation, just infiltration, there's a fair amount of pressure gradient from the stack effect across the walls anyway."

One of the simplest ways to meet the 50 cfm requirement is to upgrade a standard bathroom fan to one that runs all the time. This satisfies both the bathroom and whole-house ventilation requirements. Another method that's commonly used, especially in the Southeast, is to make an inlet into the return plenum. This tactic requires a little bit more knowledge because there's a damper, an inlet, and a control device to make sure the furnace fan cycles a minimum amount of time. Although this technique can be a bit more expensive, Sherman noted that it has the advantage of better air distribution.

"For all but the very simplest systems, there are some new skills to be used, but they're not significantly different than the standard contractor skills," said Sherman. "It's just a question of getting up on the learning curve. Hopefully, there will be plenty of people offering the training necessary to keep everyone up on these devices."

Sidebar: Standard 62.2's Major Requirements

With some exceptions, standard 62.2 requires whole-house mechanical ventilation. For a typical house, the required ventilation rate is about 50 cfm, but it varies with house size. The standard allows (and provides guidance for) flexibility in ventilation system selection (e.g., continuous or intermittent; supply or exhaust; with or without heat recovery).

Mechanical exhaust (i.e., to outdoors) is required in kitchens. The basic requirement is that a user-operable vented range hood must exhaust at least 100 cfm of air. To accommodate the wide range of kitchen configurations in the market, the standard includes an alternative of 5 kitchen air changes per hour of (continuous or intermittent) exhaust without any requirements regarding location within the kitchen.

Mechanical exhaust is required in bathrooms, but not in rooms such as toilet rooms, laundry rooms, lavatories, and utility rooms. The basic requirement is for a user-operable fan of at least 50 cfm. A continuously operating exhaust fan of 20 cfm may be used as an alternative.

The fans or fan systems required to meet the previous requirements must meet specific airflow and noise performance levels.

Combustion appliances must follow applicable codes. For a narrow set of circumstances, vented combustion equipment must be checked for backdrafting/spillage. ASHRAE is currently processing an addendum, which would eliminate any requirement for backdraft testing by eliminating that compliance path.

When air handlers or return ducts are in an attached garage, the duct system must be tested to meet air tightness specifications.

Good particle filtration is required upstream of air handling components. (The minimum filtration requirement is easily met, but is better than the fiber filters most commonly used.)

- Joanna R. Turpin

Publication date: 07/26/2004