Here is what I can tell you . A furnace that is working properly will rise the temperature from 35 to 65 degrees (temperature reading compared from return air to suply air outlet). The temp difference will be lower if you have the fan on a higher speed. If you do not have at least a 35 degree temp rise on medium speed, you may have a problem with the furnace. Make sure the flame stays lit and is not cutting in and out.
Inspect the return air ductwork and check that the blower doors are all on. If you are pulling in cold air from an attic space that will kill the leaving air temp.The house may never get to set point due to all the cold air being sucked in from undesired areas.
If you are getting the correct temp difference and you have no air leaks then maybe the heater is not large enough when you consider the level of insulation /air leaks in the home at 5 degree outside temp.
At my 40 yr old house I have a 75000btu heater on a 1500 sq ft home(4 ton condenser).Down here houses are built very loosly with much air leakage and so at 30 degrees outside my heater might run for about 20 minutes out of the hour.Last edited on Fri Jan 8th, 2010 02:55 am by ACtechGUY
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Don't know much. But learned early on, once you let the smoke out of a something electrical, you can never put it back in!!
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