Reasons why your furnace keeps turning on and off: Temperatures outside of home. Improper insulation. Faulty thermostat. Dirty flame sensor.
Most furnaces kick on and off between three to eight times an hour, depending on things like outdoor air temperatures, the furnace's age, and how much insulation you have. That's why, instead of asking how often a furnace should cycle, it's best to stay alert to changes in how your furnace is running.
It's common for your furnace to kick on more frequently in cold weather. While it's okay if your furnace cycles on and off several times every hour, it shouldn't cycle on and off more than 8-10 times. If it does, this is known as short cycling, and it's a sign that something in your heating system needs to be fixed.
Blocked vents or a clogged air filter may cause your furnace to run and then shut off too early. It's easy to fix these issues on your own. You should change your furnace filter at least once every three months. Follow our guide to do it yourself.
It should cycle throughout the day. An average furnace should turn on and off three to eight times per hour. If your furnace is turning on and off more frequently, don't assume it is short cycling. Several factors determine how often your furnace runs per hour.
Industry research shows some expected time frames for how long a furnace runs during a particular cycle. Running 10 to 15 minutes per cycle seems acceptable. So is running as long as 20 minutes. Even running every seven or eight minutes may not be a problem, as other factors could lead to more frequent cycling.
A furnace cycling on and off repeatedly can be caused by various reasons, from dirty filters and obstructions in ducts and registers to incorrect thermostat settings and faulty limit switches. By following the steps above, you can help prevent your furnace from cycling too frequently and save energy costs.
If your furnace keeps turning off, check for issues such as: Dirty Air Filters. A clogged filter restricts airflow, causing the furnace to overheat. Replace air filters every 60 to 90 days to prevent this problem.
With an effective air delivery system and a well-insulated home, this should be long enough to establish your preferred temperature throughout the building. After resting for approximately five to 10 minutes, your furnace will likely cycle on again.
Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism. Except, there is a flame and without the gas to supply it, it dies. This is a frustrating problem, but an HVAC technician can fix it.
The most common problems that cause a furnace to short cycle include: An overheating heat exchanger. A dirty flame sensor rod. A blocked flue pipe.
The simple solution: Turn your furnace off and check the filter. If it's dirty or it's been 3 months or more since you changed it, put a new, high-quality filter in place.
Under normal conditions, your furnace should run two to three heating cycles each hour, with each cycle lasting for 10 to 15 minutes. It may run longer or more frequently during extremely cold weather when the outdoor temperature is below zero, but it still should only run sometimes.
If your furnace turns on, and off, and back on again in a seemingly endless loop, you're experiencing short cycling. Essentially, short cycling occurs when the system cannot complete a full heating cycle. There's no one cause of short cycling, but with some troubleshooting you can get to the bottom of the issue.
Leaky or poorly designed ductwork can cause your furnace to cycle more frequently as it tries to heat your home. Properly sealing and insulating your ductwork can help prevent this problem.
If someone is at home in the daytime, 72° F (22° C) is a good start, but aim for 68° F (20° C). If everyone is away from home in the daytime or you're asleep at night, we feel 66° F (19° C) to 62° F (17° C) is best.
On average, furnaces should kick on and turn off anywhere from three to eight times per hour. However, if your furnace turns on and off more frequently, don't assume the furnace is short cycling just yet.
In the heating, ventilation, and air conditioning (HVAC) business, short cycling is a phrase used to describe when a heater or air conditioner cycles on and off too frequently. It signifies a problem in your heating system's proper functioning and efficiency, in which it is not completing its heating processes.
3- Furnace Shuts Off After 15 Minutes Due to a Dirty Air Filter. If your furnace shuts off after 15 minutes, a dirty air filter is likely blocking your heat.
Short Cycling Causes
Here are a few problems that may cause furnace short cycling: Air Filters – Severely dirty air filters may cause this issue because they restrict the airflow to your system. Replace the filter and set a reminder to do this regularly. Blocked Vents & Registers – This is another easy fix you can try.
A dirty air filter is the most common cause of short-cycling. If the air filter is clogged with dirt, it won't allow proper air flow to the heat exchanger. That can cause the furnace to overheat and forces the high limit switch to ride to the rescue by shutting the furnace off.
Dirty Air Filters
So, the furnace is triggered to stop, then it cools down only to fire back up again. This short cycling continues to repeat until the furnace receives the airflow it needs. Dirty air filters are one of the most common reasons behind furnace short cycling.
If the air filter is good to go, lower the temperature on the thermostat. If the furnace continues to run, shut the heating system down completely. If your thermostat is set to a high temperature or if it's very cold outside, the furnace might be running just to keep up with the thermostat's demand for heat.