What is Short-Cycling when it Comes to Furnace Operation?
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What is Short-Cycling when it Comes to Furnace Operation?

What is Short-Cycling when it Comes to Furnace Operation?

As temperatures in your home fluctuate due to changes in the weather, the thermostat that operates your furnace and air-conditioning system will activate in order to regulate them. This is what is referred to as equipment cycling.

While it is normal for your furnace to turn on and off at regular intervals, it can sometimes malfunction or ‘short-cycle,’ where it only stays on for a few seconds at a time instead. Not only will short-cycling prevent your home from reaching the desired indoor temperature; it can be an indication that there is a serious problem with your home’s cooling and heating system. Below are a few potential causes of furnace short-cycling.

Thermostat Issues

  1. Overheating

A common cause of furnace short-cycling is overheating. Most new furnace units have various safety devices installed, which are used to monitor operating temperatures. Should the heat exchanger unit overheat, the furnace will automatically shut down to prevent damage. In extremely rare instances, a fine crack in the heat exchanger can also cause the unit to short-cycle. If you are under the impression that your furnace is short-cycling because it is overheating, you should turn the unit off immediately and call in an experienced repairperson.

  1. Location of the Thermostat

Incorrect location of a thermostat is another factor that is often responsible for a furnace short-cycling. To ensure that this is not the cause, a thermostat should be situated on an inside wall of a part of your home that is frequently occupied. They should not be anywhere near drafts, close to windows or on any of the outer walls of your home.

To determine if your thermostat is the cause of your furnace’s short-cycling, place a temporary cardboard shield around it. If the short-cycling stops virtually immediately thereafter, it is recommended that you have an experienced technician relocate your thermostat.

Restriction of Airflow

  1. Air Conditioning Coils

There is an evaporative air conditioner coil located just above your furnace unit, which is responsible for absorbing heat from the air. If there is dirt, dust or debris covering these coils, it will restrict airflow, which will in turn cause your furnace to short-cycle during summer and winter.

  1. Blocked Air Vent Registers

In some cases, items can end up being placed too close to, or even on top of, air vent registers. This can also restrict airflow to the furnace, which will cause it to short-cycle. Always check to ensure that nothing is placed on top of any of the air vent registers.  Also, do not close any air registers; they must all be open to ensure the furnace has adequate airflow.

  1. Air Filters

Furnaces will usually short-cycle because of a lack of airflow, which is commonly caused by dirty furnace filters. Replace your furnace filter and then ensure that this is done every month for 1” thick filters or twice a year for thick media filters. If your furnace is short-cycling after filter replacement, the new filter may be restricting air flow as well. For example, do not use 1” pleated filters as they are too restrictive for most systems.

If you have tried the above-mentioned steps and are still having issues with your furnace short-cycling, call and book a furnace inspection with one of our technicians today.

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Ravinia Plumbing, Sewer, Heating & Electric
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*Based on research conducted January - December 2021

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