Q: We have a new home with a fresh-air induction system that runs on a timer. When the timer comes on, fresh air is drawn into the house...

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Q: We have a new home with a fresh-air induction system that runs on a timer. When the timer comes on, fresh air is drawn into the house by the furnace while a whole-house fan upstairs exhausts air out.

During the first year, we had the fan coming on for about 10 minutes every hour to clear out “off-gassing” from building materials, etc. However, the house is now almost two years old, and I believe the off-gassing is now minimal.

Considering energy efficiency and good health, including minimizing possible mold and related problems, how often should the fresh air intake/exhaust system run? Does this vary from season to season?

A: All residential structures built after 1991 have some form of exhaust/intake for fresh air.

The amount of time you run the air system is dependent on your lifestyle, size of the building, the season and the number of people in the house.

Six roommates, all smokers who never run the exhaust fan when showering or cooking in their small, tightly sealed home, will need more ventilation than a nonsmoking single who often uses the exhaust fan and opens windows in his mega-house.

That example didn’t really answer your question, did it? The goal is to have about one-third of the air change per hour in a typical home. The crowded, sealed home in the example needs more than that, and I think you understand why.

In very rough terms, running the system four or five times a day for about 30 minutes will get your home close to that one-third air turnover.

Q: I have an enclosed recessed light near the shower on the top floor of my house. The darned thing works for a while, goes out, then comes on again after about five minutes. It seems to make no difference whether I am showering or not. The house is about 24 years old. I have changed the bulb several times, and nothing has changed.

A: This type of light has thermal protection to prevent overheating. When enclosed, as it is in a shower area, it traps even more heat than a similar light that is not covered at the bottom.

First, I would reduce the wattage of the light bulb in the fixture, then run up to the attic. This type of light has vents in the top that allow heat to escape, and should not be in contact with insulation. When you remove the insulation, the top of the light will ventilate and cool better, and your problem should go away.

While in the attic, check the wiring leading to and inside the light to make sure it has not been scorched from excessive heat. You may want to consider replacing the recessed fixture with a newer unit.

Darrell Hay is a local home inspector and manages several rental properties. Send home maintenance questions to dhay@seattletimes.com. Sorry, no personal replies. More columns at www.seattletimes.com/columnists.