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Q.Nine years ago I built a new house on a slab foundation. We put in a forced-air heating system, and the hvac contractor ran the ducts under the slab. The house is on a lake, and during certain times of year rising ground water enters the ducts. We installed a small pump with a float switch in the ductwork next to the furnace, and it has been doing a fairly decent job, but maintenance of the pump has been a continuing problem. The homeowner wants a more permanent solution. What is the best way to prevent water from entering the ducts?

A.Bill Rose, architect and building researcher at the University of Illinois in Urbana-Champaign, responds: Abandon the below-grade ductwork. Otherwise, the humidity in the ductwork will create a mold museum for the occupants, and they will be breathing a little of every water-soluble contaminant in the area. Plug the ducts at all penetrations through the slab with concrete. Route new ducts above the slab somewhere, or move to hydronic or resistance heating. No exceptions.