HVAC maintenance companies explain that a furnace will normally perform an average of two to three cycles in an hour, with each cycle lasting 10 to 15 minutes. But to keep temperatures at a comfortable level during cold weather, a furnace might need to increase this range to three to 10 cycles.
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. Outside temperature, for example, could contribute to how fast or slow the furnace cycles.
Furnace short-cycling refers to a furnace that's switching itself on and off too frequently. It's normal for a furnace to turn on and off periodically. They are designed to cycle on and off, but a standard home furnace should only turn on and off between three to eight times per hour.
This is commonly caused by a dirty air filter. Once high temperatures are reached within the equipment, the limit switch shuts down the heating cycle for safety reasons. Then the furnace must cool down before another cycle starts – but the issue just happens again.
One possible issue for a furnace running only for 5 minutes could be a malfunction with the thermostat. The thermostat is responsible for regulating the temperature in your home and communicating with your furnace to turn on and off as needed.
Common issues include: Old wiring or dead batteries: Replace batteries or old wiring to ensure accurate temperature readings. Thermostat location: If your thermostat is too close to a heat source (like sunlight or a heat register), it can misread the temperature and cause your furnace to keep shutting off.
A furnace “short cycles” when it turns off before reaching the desired temperature. This means that if your thermostat is set to 72 degrees, the furnace may shut down at 65 or 68 degrees, but will never reach 72 degrees. Short cycling can also be used to describe a furnace that turns on and off too often.
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.
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.
During the coldest days in winter, it is normal for a furnace to run almost constantly to keep the home warm. As long as the furnace is running efficiently and not making strange noises, the constant operation is likely nothing to worry about. But in general, your furnace should not constantly be running.
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.
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.
If your furnace shuts off after a few minutes and starts more than eight times an hour, it may require repair. Common causes of furnace short cycling include restricted airflow, a malfunctioning flame sensor, or a poorly placed thermostat.
So how fast should a furnace heat a house? On average, once you turn on your furnace, it should take about an hour to increase indoor temperature by 1 degree. Afterwards, it's 45 minutes per degree.
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.
Single-Stage or Two-Stage Furnaces
The single-stage furnace should run 10- to 15-minute cycles and should run two or three cycles per hour. The two-stage system runs most of the time at the lower heating output but will run nearly continually.
In general, most furnaces run for approximately 10 to 15 minutes before cycling down. With an effective air delivery system and a well-insulated home, this should be long enough to establish your preferred temperature throughout the building.
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.
Luckily, a few causes of short cycling are easy to fix yourself. An incorrectly sized unit, refrigerant leaks, and other issues demand a professional repair. If your short cycling issues are due to air filter problems or a frozen evaporator coil, you can address the problem before calling the professionals.
Understanding Short Cycling and Why It's Such an Issue
An air conditioning system that often only stays shut off for 10 minutes usually isn't something you have to worry about. You do have to worry if your AC regularly shuts off in under 10 minutes, as this indicates it is short cycling.
This means the compressor will run for 10 minutes, stop for 10 minutes, and repeat the cycle two more times during a single hour. You can tell a system that's short cycling when it turns on and off three times in five to ten minutes.
Customers often ask, “Is furnace short-cycling dangerous?” While short-cycling isn't inherently dangerous, it can reduce energy efficiency, cause safety problems, and increase wear and tear on your home's HVAC system.