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.

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