Figuring out how long should a furnace run is a simple question with just a few tricky elements to it. Typically, if your furnace is operating well, it should turn on 2 or 3 times per hour, for no more than 10 to 15 minutes in mild temperatures.
So, if you’re wondering how long does a furnace run per day, just multiply that by 24 and you’ll get 48 to 72 cycles, for 10 to 15 minutes each.
That’s how long should a furnace run during a typical heating cycle but what if it runs more often? There are three usual reasons for extended or more frequent furnace cycles:
- Faulty thermostat. There are many things that can go wrong with a thermostat depending on what type it is and how exactly it functions. All of them are pretty easy to identify if the device doesn’t display accurate temperatures or if the displayed temperatures don’t change accordingly to the furnace’s operation.
The problem can sometimes be as simple as a poorly-placed thermostat, whether that’s in direct sunlight or next to a poorly-sealed window in the winter. If that’s the case, the thermostat should just be relocated. If it’s broken, then the easiest solution is just to replace it.
- An oversized furnace. If your furnace is new, the problem can be as simple as that you’ve got the wrong size furnace for your home. Whether the contractor has made a mistake or you’ve chosen the wrong type yourself, an oversized furnace is very likely to start short cycling – to constantly turn on and off again.
If that’s the case, hopefully, you’ve got a good warranty in place. Otherwise, the replacement costs would be on you which would be unfortunate. Even then, however, the correct thing to do is to replace the furnace as soon as possible as it just won’t be working efficiently.
- Overheating furnace. Short cycling is a common symptom of a furnace that’s overheating. This can be due to many different problems within the furnace such as dirty and clogged air filters, blocked or accidentally closed vents or registers, or blocked exhaust pipes. All of those you can easily check and fix yourself but if the problem is in anything else, the best thing to do is to call a professional.