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There probably is not a week that goes by where we don’t
see a “cheater valve” used on a plumbing fixture. What do you tell your
clients? Some inspectors say they are illegal, others say they are not
“code”, still others say, they are fine, because that is the only way
to vent a fixture far from the main stack. Actually all of those
statements can be correct. First we need to know the difference between
an air admittance valve (AAV) and a “cheater vent”. An air
admittance valve (pictured in white) opens when negative air pressure
is detected and allows air into the vent stack. When the negative
pressure is gone it then closes to prevent sewer gases from entering
the area. A check valve or “cheater” valve are spring operated and open
by suction to allow air into the system. Sewer gas may escape. The
spring in the check valve may fail. If this happens, it will remain
closed and allow negative pressure to siphon the drains allowing sewer
gases to enter at the fixture drains. Check valves (pictured in black)
are only
allowed in mobile homes.
The 2015 International Plumbing Code specifically
addresses AAV’s in section 918. Section 918.3 states in part;
“Individual branch and circuit vents shall be permitted to terminate
with a connection to an individual or branch-type air admittance valve
in accordance with Section 918.3.1. Stack vents and vent stacks shall
be permitted to terminate to stack-type air admittance valves in
accordance with Section 918.3.2.”
Basically Section 918.3.1 states that individual and
branch-type AAV's shall vent only fixtures on the same floor level, and
connect to a horizontal branch drain. Where the horizontal branch is
located more than 4 branch intervals from the top of the stack, the
horizontal branch shall be provided with a relief vent that shall
connect to a vent stack or stack vent, or extend outdoors to the open
air. The relief vent shall connect to the horizontal branch drain
between the stack and the most downstream fixture drain connected to
the horizontal branch drain. Section 918.3.2 states; “Stack-type air
admittance valves shall be prohibited from serving as the vent terminal
for vent stacks or stack vents that serve drainage stacks having more
that six branch intervals.” (A vent stack is a vertical pipe that
runs parallel to the waste stack, to which all the vents are connected.
The stack vent is the final portion of the waste / soil stack above the
highest fixture and normally terminating outside). So what should a
home inspector be looking for?
- An
AAV cannot be used for sumps and sewage ejector systems
- AAV will have a UPC symbol on it / check
valves do not
- AAV
should be accessible and in adequate air space
- The
size of the AAV shall be rated properly for the size pipe it is venting
- Section
918.7 states; “Within each plumbing system, not less than one stack vent
or vent stack shall extend outdoors to open air
- AAV
should not be installed in supply or return ducts
- AAV
shall be located a minimum of 4 inches above the horizontal branch drain
or fixture drain being vented.
- Stack
type AAV shall be located not less that 6 inches above the flood level rim
of the highest fixture being vented
- The
AAV shall be located within the maximum developed length permitted for the
vent.
- The
AAV shall be installed not less than 6 inches above insulation materials
- Within
each plumbing system, not less than one stack vent or vent stack shall
extend to the outdoors
- AAV
should be installed no more than 15 degrees of vertical
- AAV’s
should not be exposed to the elements
- Check
or cheater valves are only permitted in mobile homes
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