What is Furnace Short Cycling and Why Does It Happen?


Winter is in full swing, and if you live in the northeast, your furnace is likely keeping very busy.

But if your furnace hasn’t gone through routine pre-winter maintenance, you might find yourself dealing with some common heating unit issues. One of these issues is known as “short cycling.”

Your furnace’s cycle refers to the journey it takes to bring your home to the desired temperature. When your furnace turns itself on and off in short bursts, it’s in the process of short cycling. This not only makes your unit less efficient, it can also signal that you have a serious issue with your HVAC system.

What causes furnace short cycling?

There are several things that can cause your furnace to short cycle. Let’s look at some of the most common culprits, and what you can do to fix them.

1. Reduced air flow

Restricted air flow is the most common reason for a furnace to short cycle. There are a few different ways your air flow might be blocked.

Air filters

Air flow might be restricted due to a dirty air filter. If so, it’s just a matter of replacing the old filter, and getting into the practice of swapping out dirty filters for new, clean ones every two months when the furnace is in operation.

iStock-186343987_RT.jpgIf you’ve just added a new filter, but are still dealing with furnace short cycling, you may have added a filter that’s too restrictive. Be sure the filters you use are designed for your model and brand of furnace.

And if it seems like the filters are collecting an unusual amount of debris, you may want to consider having your air ducts cleaned.

Air vent registers

This is just a matter of checking air vent registers to make sure nothing is blocking air flow.

Air conditioner coils

If the evaporative coils in your air conditioning system get blocked by debris, it can cause the HVAC system to short cycle. This is a problem that can surface during the heating and cooling system.

2. Issues with your thermostat

iStock-530325621_RT.jpgThe location of your thermostat can cause short cycling. Make sure your thermostats are on an inside wall in a part of the house that gets regular use, and away from drafts, windows and outside walls.

If you’re dealing with short cycling, try covering the thermostat with a piece of paper or cardboard. If the short cycling stops, you likely have a draft. Talk to an HVAC professional about moving the thermostat.

3. Overheating

iStock-459617609_RT2.jpgFurnace short cycling might be the result of an overheated unit. More specifically, it can happen when the heat exchanger in your furnace overheats, and the burner turns itself off to prevent damage. In some cases – and this is rare – there may be a crack in the heat exchanger, which causes the furnace to short cycle. If you suspect this is happening, turn off your unit and call an HVAC repair service.

Regular furnace maintenance can prevent short cycling

Winter is no time to be dealing with short cycling, or any other sort of heating unit issues. If your HVAC system is showing any of the signs we’ve described above, contact All Seasons Comfort Control.

Our expert technicians can diagnose whatever’s ailing your system, and provide routine maintenance to make sure your furnace does its job all winter long.