A.Pat Huelman, cold climate housing coordinator at the University of Minnesota, responds: Whether or not the fireplace or exhaust fan will cause problems depends on several factors. The most important factors are the leakage characteristics of the house, the type of combustion devices used for space and water heating, the location and type of fireplace and chimney, and the presence of other exhaust devices such as a clothes dryer, central vacuum, or bath fans.

The quantity of combustion and dilution air needed by a fireplace varies, depending on the type of fireplace, the type of chimney, and the size and burning phase of the fire. The amount might be as little as 100 or 200 cubic feet per minute (cfm) at the startup or burn-down of a small fire in a fireplace with glass doors, or as much as 800 cfm...

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