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Musings of an Energy Nerd

All About Indoor Air Quality

Which materials, substances, and practices are important to keep your indoor air fresh and healthy?

From the perspective of indoor air quality, the most dangerous activity in your house is cooking. Cooking releases dangerous amounts of fine particulates and acrolein into the air.
[Image Credit: Eugene Kim / Flickr]

Many owners of green homes are concerned about indoor air quality. GBA often receives questions from homeowners who worry that some building materials emit dangerous chemicals. For example:

We do our best to provide answers to these questions. But if there is a theme running through these questions — and I think there is — it would be this: homeowners are worrying about the wrong materials and substances.

Indoor air quality (IAQ) is a big topic. To get a handle on it, we need to break it down into small bites.

Here’s how I’d like to proceed:

Finally, I’ll share researchers’ findings about which chemicals are most concerning.

In most U.S. locations, indoor air is more polluted than outdoor air. According to the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), “Studies from the Environmental Protection Agency on human exposure to air pollutants show that indoor levels of pollutants may be two to five times, sometimes more than 100 times, higher than outdoor levels.”

There are exceptions to this rule, of course. If your house is located near a busy intersection or a location where buses or trucks often idle their engines, the outdoor air near you house may be more polluted than your indoor air. If you live in such a location, increased ventilation may not improve the quality of your indoor air. For the rest of us, however, ventilating a house with outdoor air usually improves the situation.

The most important test you should perform is a radon test. If you’ve tested for radon, you’re done. In most cases, further testing isn’t justified.

For more information on testing, see “Indoor Air Quality Testing Should Not Be The First Move.”

Asbestos fibers. Most building products containing asbestos were removed from the U.S. market by…

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  1. Charlie Sullivan | | #1

    This is a great summary. Building can be so overwhelming that it can be hard to gain perspective. This article provides the needed perspective, at least for this issue.

    The only danger I see here is that raw foodists will delight in the condemnation of cooking. How long before you get a question from a raw-food devotee who wants help convincing a builder to go ahead with a range-free kitchen design? Oh, wait that already happened.

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Charlie Sullivan
    Two protesters holding signs in front of a restaurant:

    Organic food advocate: "Free-range chickens!"

    Raw food advocate: "Range-free kitchens!"

  3. Malcolm Taylor | | #3

    It's hard to keep up. I took CMHC sponsored Healthy Housing courses in the late 90s that emphasized the dangers of particle board and carpets. Good to know progress has been made.

  4. Dan Kolbert | | #4

    There's really only one safe cooking method
    Take out.

  5. Malcolm Taylor | | #5

    You've never done prep work in a restaurant.

  6. Brian Just | | #6

    Great overview
    This is an excellent overview of an all-too-often overlooked topic.

  7. Peter Whitman | | #7

    Range Hood Vent
    Great article, thanks Martin!
    Somewhat off topic: My range hood is going to vent to the outside with a 7" rigid duct. The range is rated at 650 CFM. This is more than what I wanted but had a hard time finding a quality island hood with lower CFM's. They sell a CFM reducer to lower the rate of exhaust. Should I install it? What's the best back vent system for a horizontal duct to keep the cold air out in the winter: damper? Exterior vent only?
    House is new construction, closed cell, HRV/ERV.
    Any links or manufacturers would be appreciated.
    Thanks is advance.

  8. User avater GBA Editor
    Martin Holladay | | #8

    Response to Peter Whitman
    Most range hoods rated at 650 cfm actually exhaust about 50% (maybe 70%) of the nameplate rating once they are hooked up to ducts and one or more elbows. You might want to test the airflow on your unit after it is installed. What airflow rate are you aiming for? Does the range hood fan have several speed settings (low, medium, high)?

    To keep cold weather out in the winter, make sure that the duct termination on your sidewall has a backflow damper.

  9. Kevin Hogan | | #9

    Range hood vent option
    Many builders in Wisconsin have chosen to vent down and out the rim joist to successfully prevent cold air from entering the home through the backdraft damper located at the termination. The rationale is cold air will not travel up the vertical run to the range hood because cold air is heavier than the indoor air. Simple solution and very effective.

  10. User avater GBA Editor
    Martin Holladay | | #10

    Response to Kevin Hogan
    I hate to disappoint you, but the theory you present is mostly hogwash.

    The relevant forces acting on the air in the duct are many, but the temperature of the air is probably the least important. The main relevant forces are the stack effect and wind (as well as pressurization and depressurization forces created by appliances in the house).

    If the kitchen range hood is on the first floor of a two-story or three-story house, then the stack effect in winter might be depressurizing the kitchen with respect to the outdoors. This will tend to pull air into the range-hood duct (if the range hood fan isn't operating).

    If the duct termination is located on the windward (as opposed to the leeward) side of the house, the wind forces will be pushing air into the the duct. This will be partially but not completely counteracted by the backdraft damper, which in no cases will be airtight.

    The fact that outdoor air is cold does not prevent it from entering a house in winter. The driving force for this type of infiltration, as I said, is usually the stack effect or wind, but it can also be due to depressurization caused by a clothes dryer, a water heater, or a bathroom exhaust fan.

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