I get many inquiries about new furnaces
and their problems. One of the things that sets new furnaces, boilers and
water heaters apart is that they use combustion blowers to force the flue
gasses through the heat exchanger since they are tighter and have more
resistance. Older furnaces simply used gravity to push the combustion gasses
through the burner tubes.
One of the problems with having a
combustion blower is that eventually it will fail. When it does you need
to get it replaced. Fortunately most motors are made by the usual manufacturers
such as General Electric, A.O Smith, Marathon, Magnetek, Emerson, Century,
Universal, Fasco and Baldor. You can get a replacement at a local supply
house such as Johnstone, United Refrigeration, Aireco, and Grainger.
Every once in a while you find a motor
that you just cant get anywhere because the mounting is funny (Carrier
and Bryant are notorious) there you must go to a dealer. In our area we
like United Products for Carrier stuff.
If your motor is stuck or squeaking
you can oil it if it has oil ports I recommend a few drops of SAE 20W oil
NON DETERGENT every year. If that fixes it you may be good to go for a
few weeks or a few years.
All furnaces that use combustion blowers
will have pressure switches to sense that the fan is running and the flue
pipe is not blocked. If one of these switches fails it will cause the same
symptoms as a bad fan motor. Some older furnaces had centrifugal switches
to tell it that the fan has come up to speed but most use pressure switches
now. If you need to replace a pressure switch you can get one from the
suppliers listed above but be very careful to install it correctly and
that you set it to the correct pressures or you could have a disaster.
Blower: usually a squirrel cage centrifugal air moving device. Will move
large volumes of air relatively quiet. Will use less energy with more back
Fan: a paddle type air moving device used where noise is not a major consideration.
Will use more energy with more back pressure.
Combustion blower: A blower used on high efficiency gas furnaces or oil
burners to move combustion air. usually 1/20 to 1/6 horsepower.
OEM: Original equipment manufacturer.
Horsepower: 746 watts
RPM: revolutions per minute.
Service factor: the extent to which a motor can be safely overloaded beyond
its name plate ratting without over heating.
Air over horsepower: The rating of a motor assuming air flow through the
windings usually as a result of the air moving device.
SAE: Society of Automotive Engineers.
High efficiency furnace: Furnace that uses over 85% of the energy in the
Condensing furnace: Gas furnace that uses over 92% of the energy in the
gas and condenses the gas into liquid condensate and hot air. If your furnace
has PVC pipe venting it then you have a condensing furnace.
Written By: Scott
Meenen N3SJH of: G&S MECHANICAL SERVICES. Specializing in Mechanical, Controls
and Electrical Modifications Of
Heating, Air-conditioning, Refrigeration,
Ice Production and Food preservation.
Anything having to do with Heat and Energy.
Serving MD, DC, and Northern
VA. Contact us by pager: 1-877-467-2914
Pager Id: 32505