Most New Furnaces Have Combustion Blowers

    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.

  1. Blower: usually a squirrel cage centrifugal air moving device. Will move large volumes of air relatively quiet. Will use less energy with more back pressure.
  2. Fan: a paddle type air moving device used where noise is not a major consideration. Will use more energy with more back pressure.
  3. Combustion blower: A blower used on high efficiency gas furnaces or oil burners to move combustion air. usually 1/20 to 1/6  horsepower.
  4. OEM: Original equipment manufacturer.
  5. Horsepower: 746 watts
  6. RPM: revolutions per minute.
  7. Service factor: the extent to which a motor can be safely overloaded beyond its name plate ratting without over heating.
  8. Air over horsepower: The rating of a motor assuming air flow through the windings usually as a result of the air moving device.
  9. SAE: Society of Automotive Engineers.
  10. High efficiency furnace: Furnace that uses over 85% of the energy in the gas.
  11. 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.
    This page will be updated soon
 Good Luck Scott
To identify the components of your gas furnace and gas valve system click here.
If your heat pump forms ice outside in the heat mode click here.
If your air conditioner or heat pump ices up in the cooling mode click here.
If you have water leaking problems click here to solve it.
For other heat pump or air conditioning problems click here.
For other heating system problems click here.
 Any other questions feel free to contact us by any of the means below. good luck Scott.
    If you were looking for Ice Machine repairs click here.
Written By:  Scott Meenen N3SJH of:
Specializing in Mechanical, Controls and Electrical Modifications Of
Heating, Air-conditioning, Refrigeration, Cold storage,
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

Page us by e-mail 240Chrs max.

Email us at:

                 This text written by: Scott Meenen * G & S Mechanical

Go to or return to the G&S Mechanical home page