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Q.I have been called to solve an air-quality problem at a house with air-lock entries. The house has hydronic heat. The vestibules have no mechanical ventilation, and the air quality is poor. What type of ventilation do you suggest for these very small rooms?

A.Ventilation consultant Andy Shapiro responds: In general, opening and closing the doors provides enough ventilation for vestibules. My guess is that there is a source of odor in these vestibules that is leading to the air-quality complaints. Could the problem be caused by the smell of boots taken off and left in the mudroom? Mold from excess moisture from some source? Off-gassing of materials or finishes?

The first approach with any indoor air-quality problem is to identify the pollution source. After the source has been reduced as much as is practical, ventilation can be used if necessary to dilute the remaining, hopefully low, concentration of offending air.

If the house has a whole-house ducted ventilation system, such as a heat-recovery ventilation system, and the source of the smell cannot be reduced to acceptable levels, then a small exhaust from the vestibule could be connected to the whole-house system. But first, find the source.