Is your furnace short cycling?

Is your furnace short cycling? Last year we discussed short cycling air conditioners and since the heating season is fast approaching, we figured it was a good time to discuss short cycling furnaces.

What is short cycling?

Short cycling is an industry term used to describe a situation where a furnace turns on and off repeatedly in a very short period of time.

What causes furnace short cycling?

There are numerous reasons why your furnace may be short cycling, and below are a few reasons that lead to short cycling.

• Dirty filters: Dirty, clogged air filters block airflow to your furnace’s heat exchangers, which can cause an overheating situation and trip the furnace’s high limit switch. Once things cool down a bit, the furnace will fire back up, but then will shut off again once overheating begins. This will continue, creating a short cycle.
• Thermostat: A faulty thermostat can lead to short cycling. A simple battery change could fix the problem, but it could also be something more complex that would require a new thermostat.
• Clogged Flue: A flue is a furnace’s exhaust system, if it cannot expel spent gasses properly, the flue-limit switch will trip. Many times a clogged flue is due animals such as birds, etc. depositing debris in the flue, causing a flow restriction.
• Your furnace is too big: A furnace that is too large for your home will turn on, heat your house rapidly, and then turn off. The process will repeat because the furnace is “too strong” and not properly sized for you home

If your furnace is short cycling, the first thing you can do is change your filters. If that doesn’t solve the problem, change the batteries in your thermostat. If neither of these things works, call a licensed, professional HVAC contractor immediately.