One of the most neglected tasks that home owners forget or simply put off to a later date is the replacement of the furnace filter. This should be done at least once a year just before heating season and more often if you have a furnace mounted air conditioner or run the furnace fan in a continuous mode for air circulation. The filter traps dust and debris before it enters the blower chamber and the heat exchanger chamber. If the filter becomes clogged it no longer allows free air movement and constricts the amount of air available to the blower. This causes the blower motor to work harder to move air. The motor will use more electrical current and will also run hotter, electrical costs go up and it may cause the motor to overheat and fail. If the motor fails you now have a repair bill of a couple of hundred dollars caused by a five dollar filter.
Clogged filters will also cause the furnace to run longer due to the fact that there is less air circulating in the house. In some cases the burner will actually cycle off and on as the blower motor continues to run. Because there is less airflow over the heat exchanger it overheats which causes the high temp limit control to shut down the burner. The blower will continue to run to cool the heat exchanger. When cool enough the burner will come back on and this scenario is repeated until the thermostat is satisfied and shuts the furnace off. Overheating the heat exchanger can shorten it's life and that is usually "new furnace time" if the heat exchanger cracks. Also a cracked heat exchanger will allow carbon monoxide gases into the home which can cause death.
It is also not wise to run the furnace without a filter. If no filter is present the dust and debris circulate through the house. Dust bunnies etc. can lodge in the heat exchanger chamber and may ignite if conditions are right. If the ducts have not been cleaned for some time and and a small fire takes place you could have a fire in the duct work and that may spread into the house.
So for five dollars or so and a once a year chore, I would replace the furnace filter. It's worth it in the long run.
Charlie teets
Above Board Home Inspections
Calgary, Alberta
Ph: 560-5944
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