- 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.