Conscious Choice: Fresh Air Systems

March 2000 | Sensible Home

Fresh Air Systems

by James Dulley

Dear Jim: Our furnace has an air cleaner, but the indoor air seems stale. I worry about how it affects my children’s health. What is an economical method to get fresh air indoors? How about just opening a window a little? — Deb N.

Dear Deb: Stale indoor air is not only unpleasant, but, according to the EPA, it can be unhealthy. You don’t often realize how stale the air is until you open a door to let a pet in, for example. The gush of outdoor air is very refreshing. This is a problem even in older, so-called leaky homes.

The key to a healthy and comfortable indoor environment for your family is to circulate a substantial volume of fresh outdoor air throughout your house. This is also important in the summer because the higher indoor humidity levels can allow molds, dust mites, and other allergens to accumulate.

Opening a window has the least expensive initial cost, but it pushes up your utility bills. Running kitchen and bathroom exhaust fans helps some, but provides little control over where the fresh air leaks indoors. Fresh air inlet-only designs, like Therma-Stor’s unit, bring fresh air into the main air return duct.

Installing a window or whole-house heat recovery ventilation (HRV) system is your overall best option for ensuring healthy indoor air quality. These can be attached to your existing furnace/air conditioner ductwork. Alternatively, you can have separate ducting added if your home has hot water or electric baseboard heat.

An HRV is a simple device. One fan pulls fresh outdoor air through a heat exchanger into the house duct system. Another fan sucks stale air out of your house through the same heat exchanger. The two air flows do not mix. Easy-to-install window units accomplish the same effect without ductwork.

In the winter, the outgoing stale warm indoor air preheats the incoming fresh outdoor air as the two streams pass through the heat exchanger. Up to 80 percent of the heat is saved. The fans use less than 150 watts of electricity. In the summer, the stale cool indoor air precools the incoming fresh air.

You can select either a standard or enthalpic heat exchanger design. Standard models are often made of aluminum and just transfer heat. Enthalpic designs also allow some moisture to pass between the two air flows for better comfort.

Another primary difference among the various models is the comfort controls. Look for a model with three to five fan speeds. A programmable control that operates the HRV on a continuous low speed while your family is home is most effective. Simple timer controls are the least expensive option.

Adding a dehumidistat control can help especially in the winter. When the indoor humidity reaches a high level (sweating windows), the HRV automatically switches to high speed.

Write for (or instantly download from www.dulley.com) Update Bulletin No. 516, buyer’s guide of fifteen whole-house/window HRVs, capacities, efficiencies, power, features, and prices. Please include $3 and a business-size SASE. James Dulley, Conscious Choice, 6906 Royalgreen Dr., Cincinnati, OH 45244

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