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W
ith warm weather just around the corner, thermostats soon will be
switched from heat to cool. Those of us who inspect and repair HVAC
systems for a living know that with the start of the AC season, the phone
will begin to ring with cries from hysterical customers frantic about water
dripping from their ceilings and water-soaked floors. Condensate may be behind
their falling plaster and drenched carpets due to improper collection and control of
this cooling-mode byproduct.
As air passes through the cooling coil of an air conditioner or heat pump, its tem-
perature is lowered below the saturation point. While simultaneously hugging the
fins of the coil and moving downward, moisture sucked from the air begins filling a
collector positioned under the coil, which manufacturers call the primary conden-
sate drain pan or just the condensate pan. As the pan fills, it must continually drain
to prevent it from overflowing and causing damage to the equipment and to the
surroundings. The pan also must drain quickly and completely to prevent it from
becoming an unhealthy pool of contaminants. Failure to do so can lead to personal
and real property damage and even to life-threatening illnesses.
bloW-THroUgH and draW-THroUgH SYSTEmS
The evaporators of air conditioners and the indoor coils of heat pumps, both used
for cooling in summer, are installed so that a blower either pushes or pulls air over
their cooling surfaces. When air is pushed across, putting the coil under positive
pressure, it is considered a blow-through or positive pressure system. When air is
pulled across the coil, it is a draw-through or negative pressure system. The major-
ity of air handlers used with heat pumps or with modern AC cooling-only systems
are draw-through systems. Blow-through systems are common when cooling coils
are attached to a gas or oil furnace, as most furnace makers call for cooling coils to
be placed downstream of the heat exchanger.
There are a few exceptions regarding cooling coil placement in the air stream gen-
erated by a furnace blower, but unless the furnace is listed and labeled safe to be
downstream of a cooling coil, passing cooled air over the heat exchanger will result
in extensive corrosion of the furnace, premature failure of the heat exchanger and
moisture damage to the surroundings.
Home inspectors need to pay close attention to the cooling coil location when in-
specting new furnace-based heating and cooling systems. If the system has yet to
be operated in the cooling mode, there will be little evidence of a problem, and the
Let’s Concentrate on
CONDENSAtE
Kenny Hart, ASHI Certified Inspector
Cased coils or coil boxes are often attached to
furnaces.
Photo from Carrier Literature
.
The condensate
pan for vertical
installations can
be seen under the
“A” coil and is
labeled #5 in this
illustration. The
condensate pan
for a horizontal
installation can be
seen at the left
side on the air
handler and also
is labeled #5.
Illustration from Carrier
Literature.
Copyright © ASHI Reporter. Reprinted with permission. This article originally
appeared in the April 2009 issue of the ASHI Reporter. To learn more about the
American Society of Home Inspectors go to www.ashi.org and www.ashireporter.org.
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T H E C A N A D I A N
HOME INSPECTOR