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Riley Heating & Air Blog

Should My Furnace Only Run for 5 Minutes at a Time?


The straight answer: No. If your furnace is only running for five minutes (or even less) before shutting down, and then turning back on after another five minutes, it’s got a problem known as short-cycling. In many cases, you’ll need to arrange for professional heating repair in Columbus, GA to fix the problem—and it can be serious.

For the longer answer about why short cycling is trouble and what causes it, follow along below.

The Standard Furnace Heating Cycle

Furnaces go through heating cycles that start when the thermostat sends a request for heating. Gas flows to the burners, the electronic ignition system ignites them, the heat exchanger warms up, the blower activates, and warm air starts to go to the rooms connected to the ventilation system. When the thermostat registers that the house has reached the target temperature, it tells the furnace to shut down, starting with the burners and ending when the blower shuts off.

The time it takes for a complete cycle varies, but most of the time it will last from 10–15 minutes. A furnace will complete around three cycles per hour. 

The Short-Cycle

When a furnace starts to cycle for less than 10 minutes on a regular basis, it’s probably short cycling. The time between cycles will also shorten, and the furnace could turn on more than five times per hour. This is bad news for several reasons:

  • Wear and tear: Constantly stopping and starting places extra strain on the furnace’s mechanical parts, causing increased wear and tear that will lead to more repairs and shorter service life.
  • Wasted energy: A furnace consumes the most power when it starts up, so when it starts up more than usual, it drains more energy and raises utility bills.
  • Poor heating: A furnace needs to run for a complete cycle to distribute heat evenly around a house. When it shuts off early, it will leave parts of the house with insufficient heating.

The Causes of Short Cycling

One of the difficulties of dealing with a short-cycling furnace is its many different possible causes. Unless the problem is a simple one, such as a clogged air filter, it requires the work of professionals to diagnose the underlying trouble and accurately fix it. Here are several of the malfunctions that can lead to short-cycling:

  • Overheating: When the furnace overheats, a mechanism called the limit switch shuts off the gas and the burners to prevent damage and maintain safety. The furnace can overheat because of a faulty blower, clogged air filter, and other reductions in airflow.
  • Faulty safety mechanisms: Various safety mechanisms in a furnace can malfunction so that they shut the furnace off even when nothing is wrong. These devices include the flame roll-out switch, the flame sensor, and the limit switch.
  • Faulty thermostat: The source of the problem may come from outside the furnace—a thermostat that’s either sensing incorrect temperatures or a bad connection to the furnace control board.
  • Age: When an older furnace begins short-cycling, it’s often a warning that the furnace is too worn down to work correctly. A gas furnace that’s more than 15 years old is a prime candidate for replacement when it short-cycles.

Contact Riley Heating & Air if you have a short cycling furnace. You can Rely on Riley!

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