Learn about Downflow / Horizontal
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Venting
Venting refers to the pipe that connects to the furnace and
goes to the outdoors to remove the furnace’s combustion
gasses (also referred to as a ue or chimney). Lower eciency
furnaces (in the 80% eciency range) have metal vent pipes
which often connect into a brick chimney; or the metal vent
pipe goes vertically through the home and terminates through
the roof. Instead of metal, most new high eciency furnaces (in
the 90% eciency range) use a plastic PVC vent pipe (such as
used for plumbing) and can be vented vertically or horizontally
out the home. Plastic vent piping is used because the vent gas-
ses from the high eciency furnaces aren’t hot, and so a metal
pipe isn’t required. The heat goes into the home instead of out
the chimney, which is an important money-saving benet.
If your existing low eciency furnace vent terminates into a
brick chimney along with a water heater venting into the same
chimney, and you’re replacing the furnace with a new high
eciency model which will no longer vent into the chimney,
a chimney liner will need to be installed for your water heater.
A chimney liner is required by code in this case, and needed
to insure the water heater’s combustion gasses stay warm
enough to rise through the chimney to the outdoors as well as
to protect the chimney from deterioration. If you are installing
a new low eciency furnace which will reconnect to the brick
chimney with a metal pipe, code requires that both appliances
be vented through the chimney liner. Aluminum chimney liners
(used for gas products) cost about $100-$300 and are relatively
easy to install.
2) Selecting the right accessories
Some heating systems have accessories that might be
required for your application. Some of these could be:
LP Conversion Ki• t – This is a kit that is used to convert
the new gas furnace so it can operate on liquid propane
(LP) instead
High Altitude Conversion Ki• t – Just as it sounds like,
this is a kit that would be required for gas or oil heaters
used at high altitudes, typically when the installation is
above 5,000 or 7,000 ft
Thermostatic Expansion Valv• e – This is a valve required
for operation for high efficiency heat pumps
Accessories of this type are mentioned on the manufac-
turer’s specification sheets.
Then there are accessories that are not required, but you
might want to get to improve the performance of your
heater, make installation simpler, to increase your comfort
and to improve the health of your home’s occupants. For
more information on improving indoor air quality, see the
government’s web site at www.epa.gov/iaq.
There is a greater variety of optional accessories avail-
able for forced air furnaces than for other types of heaters
such as boilers. Here are some useful accessories for your
forced air furnace to consider at the time of your furnace
purchase:
Thermostat
A thermostat is required to operate all types of heaters. You can
likely use the one you currently have, unless you are changing
system type (ask your heating professional). Even if you already
have a thermostat, there are advantages to upgrading to a new
one. For one thing, if you don’t already have a digital program-
mable thermostat, you should certainly consider getting one.
They are much more accurate which will signicantly stabilize
the home temperatures making you feel noticeably more com-
fortable. Also, programmable thermostats allow you to have
the temperatures change at dierent times throughout the day
automatically, to increase your comfort and save money. Ac-
cording to Consumer Reports, “You can shave up to 20 percent
o your heating costs by lowering your home’s thermostat 5
degrees at night and 10 degrees during the day if no one is
home.”
Another useful digital thermostat feature is called “cycle time”
that some models oer, such as the popular Honeywell Vision-
Pro touch-screen thermostat. Cycle time makes your home’s
temperatures very even and comfortable by anticipating when
the temperature will drop before it even happens and turn on
the furnace proactively.
Select a thermostat that works with your type of heating sys-
tem, as indicated on the thermostat description. Some thermo-
stats, like the Honeywell VisionPro models work with all types
of heating and cooling systems.
Sheet Metal Transition Kit
Since your new furnace will likely be a dierent physical size