Furnace filter restricting airflow?

[Littlebrook]

Hi,

I have a 1993 vintage Carrier furnace that has been cycling frequently and takes forever to reach the set temperature (probably 1-2 degree change per hour!). Yesterday the furnace stopped working so I changed the filter and reset which got it going again so it seemed like the furnace was not getting enough airflow from the returns. The filters I have been using are MERV 8 rated pleated filters. Today I switched out the MERV 8 filters for plain fibeglass filters and the furnace seems to be performing much better, not cycling as much and temperature raises 1-2 degrees in 10 min. Is it possible that the better quality filters were restricting the airflow cuasing my furnace to work harder?

 

[Leejosepho]

Dirty or otherwise-obstructed filters certainly do restrict airflow across the heat exchanger, thereby leaving the chimney as the only place for heat to go ... and I thank you for the reminder: I need to go check my own filters!

Another thing that can cause an unnecessary heat loss up the chimney is a fan limit switch set to come on too high. Hating to see nickels and dimes floating off into the sky, I have my blower set to come on at a little over 100* F., and to keep runing until the heat exchanger gets back down to around 80*. With those settings, we only get warmed air rather than hot blasts when the blower starts, and the air coming out actually feels almost cool by the time the blower stops. However, the fire starts and stops more often during a heating cycle, and that means less heat wasted into the sky.