A.Terry Brennan responds: With a strong enough contaminant source, any house can have an indoor air quality problem. If contaminants are properly controlled, a tight house can have as clean or cleaner air than a leaky house.

For example, some of the houses with radon problems I’ve worked on would need 20 to 30 air changes per hour to get them below the recommended levels for indoor radon. This could be done by adding big enough fans, but the house would cost a fortune to heat and you couldn’t keep candles lit from the breeze. So the first rule is "No strong...

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