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TECHNICAL
35
T H E C A N A D I A N
HOME INSPECTOR
Waste Plumbing continued from page 34
and cheater vents are not because of
their moving parts.
Reasons for their use
Air admittance valves and automatic
air vents are an inexpensive alterna-
tive to conventional venting. These
devices are often added when fix-
tures have been installed after the
house was built. They are commonly
used to vent island sinks and wash-
ing machine standpipes. In other
cases, they are added to correct a
siphoning or odour problem.
Implications of their use
Both air admittance valves and auto-
matic air vents perform only some
of the functions of a standard venting system
because they do not allow air out. Automatic
air vents have another negative factor, as they
rely on metal or rubber components which can
wear out and fail. Since they are mechanical
devices operating in a hostile environment,
they are prone to failure. Many authorities won’t
accept their installation and require replacement
with a conventional venting arrangement.
What we tell our clients
When we see an air admittance valve, we advise
our client that a full venting system is probably
not in place. Even where air admittance valves
are allowed, one conventional vent stack or
stack vent must still extend to the outdoors to
provide unobstructed air flow. When we see
an automatic air vent, we advise our client that
it should be replaced. When we see either of
these devices, we perform our normal plumb-
ing tests to determine whether the device is
operating.
If it works
If no performance problems are noted, we
advise the client that this may not be
an ideal installation but it may work.
We let the client know that replace-
ment may be needed.
If it doesn’t work
If there are performance issues, we
recommend replacement with either
an air admittance valve or an appro-
priate venting system.
Carson Dunlop, founded in 1978,
operates two home Inspection com-
panies in the Greater Toronto area,
and is a leader in home inspector
training and report writing in North
America. Products include the Home
Inspection Training Program, Hori-
zon, the Home Reference Book, The
Illustrated Home and the Technical Reference
Guide. Through CDW Engineering, they also
offer Commercial inspection services and train-
ing. www.carsondunlop.com 800-268-7070.