HVAC Q&A: Furnace Filters and Thermostat Problems

Q:  My thermostat says that the inside temperature of my home is currently 68 degrees - set it to 75 degrees and although heat is coming out of the vents, it isn’t very powerful and the temperature remains unchanged - What’s the problem?

A:  First, you want to make sure that your furnace filter is clean and to replace it if need be. Believe it or not, dirty filters can cause a number of unwanted issues as they impede your home’s air circulation. A dirty filter specifically blocks the cold return air flow back to the furnace.  All furnaces nowadays contain a temperature sensor, usually referred to as the 'limit switch'.  The furnace always counts on the cold return air to cool the furnace down, otherwise it will overheat and the limit switch opens circuit.  This is a safety mechanism as well as a preventative measure to make sure that the heat exchangers do not overheat.

However, if the furnace filter has been replaced for a new one and you still haven’t noticed any improvements, the thermostat may be the source of your problem. When set to 75 degrees and the inside temperature of your home stays at 68 degrees, your thermostat may be malfunctioning as it should not be shutting off the furnace. If your furnace is not shutting off and is doing the opposite where it is working non stop without reaching the desired temperature, your thermostat isn’t malfunctioning - the furnace may be. In either case, it is highly recommended to have an HVAC technician come in and check both the furnace unit and the thermostat. 

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