National Oilheat Research Alliance 35
neutralizing kit be connected to protect pipes
and sewer systems.
Some condensing appliances are equipped
with a blocked drain switch (Figure 2) to pre-vent
the unit from operating in the event of a
blocked or slow-draining drain. This switch is
wired in series with the primary control’s T &
T circuit and opens if the condensate level gets
too high.
A condensate pump may be needed to re-move
the condensate to a safe place when:
• a suitable drain is not present at the
appliance;
• the drain is above the trap outlet level
on the appliance;
• the drain line cannot be sloped down-
ward for its full length to the drain.
The condensate piping in the appliance and
the drain system should be flushed regularly, at
least once each year.
PVC vs Stainless Venting Systems
PVC piping is normally used as the venting
material for condensing furnaces. However,
since PVC starts to soften and lose its shape
at about 150°F and condensing boilers can
have flue gas temperatures between 190°F and
300°F, polypropylene or stainless steel must be
used for venting hydronic appliances.
PVC Venting Systems—Furnaces
There are a number of requirements that
must be met when venting with PVC and
the specific manufacturer’s instructions must
always be followed. In general, manufacturers
agree that:
• Vent size reduction is not permissible.
• Horizontal runs must be supported
every 3–5 feet to prevent sagging, joint
separation or pipe blockage.
• The vent system must slope upward
from the appliance to allow proper
drainage of condensate.
• Vent pipes passing through unheated
areas must be insulated.
and there are significant differences in a
number of areas, including:
1. Pipe—some manufacturers specify
rigid Schedule 40 PVC only while others
also accept ABS.
2. Fittings – some specify DWV and
some accept Schedule 40.
3. The minimum and maximum length
of piping.
Figure 2