When your furnace is functioning properly, it will regularly cycle on and off to maintain a comfortable indoor air temperature. As the temperature drops below the setting on the thermostat, the furnace will come on and produce heat. When the desired temperature is reached, the thermostat will cause the furnace to shut off. This cycle repeats many times throughout the course of a day, as your furnace works to keep everyone in your home comfortable.

What is Short-Cycling?

Short-cycling occurs when the furnace turns on and off repeatedly in a short period of time. The system may turn on for a few seconds, or even a few minutes, and then shut off again.

This rapid cycling is generally ineffective at sustaining a satisfying temperature. It can also be expensive as the rapid cycling uses more energy. Short-cycling can also reduce the lifespan of your heating system, putting undue stress on the starter and other internal components.

A properly-sized furnace turn on and off anywhere from three to eight times in an hour. The number of times your furnace cycles on will depend on the outside temperature, if your home is well-insulated, as well as other factors.

In extremely cold weather, a properly functioning furnace will typically run for several minutes before shutting off. If your furnace only runs for less than a minute or two, it could mean your system is “short-cycling.”

What Causes a Short-Cycling Furnace?

There are several things that will cause a furnace to short-cycle. This can be a potentially serious problem, so isolating the cause quickly is the first step to resolving it. Some potential causes include:

• Inadequate airflow. Dirty air filters or blocked air vents can restrict indoor airflow and cause your thermostat to register temperatures incorrectly. Replace air filters regularly and check to make sure your air vents are not restricted by drapes, furniture, or clutter.
• Improper thermostat location. Thermostats are easily affected by drafts from windows and doors, as well as the cooler temperature of an exterior wall. Be sure your thermostat is mounted on an interior wall in a regularly used room.
• The heating unit is the wrong size. If your heating unit is too large for the space being heated, it can cause the furnace to cycle on and off continuously. A qualified heating technician will help you calculate the proper unit specifications for your home.
• A damaged furnace. If a furnace overheats, a safety switch will automatically cause it to shut off as a preventive measure. However, the thermostat will cause the unit to turn back on in an attempt to maintain the temperature inside your home. Then the cycle repeats itself. A crack in the heating exchange or dirty coils will cause a unit to overheat. These problems require attention from a qualified technician.

The Importance of Regular Maintenance

As your furnace heats your home, it causes regular wear on the unit’s internal mechanisms. Regular maintenance will help reduce the wear and tear on internal parts and ensure your unit runs safely and efficiently. Scheduling an annual check-up with a local HVAC professional will help prevent potential problems. Ultimately, regular maintenance will save you money on your energy bills and prevent expensive repairs before they occur.

During a regular maintenance visit, a qualified technician will inspect your unit for cracks, corrosion, leaks, or other potential problems. Regular professional maintenance will prevent a short-cycling furnace and optimize your system for the cold winter months.