Does your furnace keep turning on and off in fairly quick succession? If so, your unit is likely “short cycling.” Short cycling is an indication that your furnace’s safety features are working perfectly, but it can also indicate a problem with your furnace. We recommend calling licensed heating and air conditioning professional to inspect your unit.

While short cycling is intended as a safety feature to shut down your furnace before a serious issue arises, it also means that your furnace is not operating at its peak performance. Turning on and off frequently means your furnace is consuming extra electricity to start, shut off, and then start again. Short cycling can also shorten the life of your furnace. Newer, more efficient systems are designed to operate for longer periods of time at the lowest speed setting, moving the air to create a more uniform temperature throughout your home. If your furnace is turning off and on and not keeping your home at a consistent temperature, there may be a problem. Let’s look at some of the most common reasons for short cycling.

A dirty or clogged air filter

The most common cause of short cycling is a dirty air filter. With a dirty filter, air is restricted, so the furnace shuts down to avoid over-work and over-heating; in a few minutes the system will make another attempt, and the short cycling continues. Meanwhile, the unit is working much harder than it should, driving up your electric bill.

Solution

Be sure to change your air filter at least twice a year, as you switch from air conditioning to heating and vice versa. If you live in an area that’s especially windy, dusty or you notice, for example, more pollen than usual, check your filter in between and change it if you notice an accumulation on the filter material.

Blocked supply air registers

Blockages in the air distribution can result in short cycling. If there’s a large piece of furniture (like a dresser, couch, or desk) in front of a supply register, or worse, several registers, this can result in overheating, and your furnace will likely short cycle.

Solution

Keep all supply and return air registers completely clear of obstructions. Move furniture away from supply air registers and resist closing off registers, as this, too, creates back pressure on the furnace blower.

A misplaced thermostat

Sometimes a heat source, perhaps a gas fireplace or a space heating unit, located near your thermostat can cause your furnace to short cycle. In this case, the thermostat senses the high temperature and automatically sends a message to the furnace to switch off, and the cycle continues.

Your thermostat should be located away from any heat sources or supply air registers, and in an interior area that best reflects your home’s average temperature.

Solution

Check the location of your thermostat. Is it close to a heat source? If possible, try moving the heat source. If that’s not possible, call an HVAC contractor and get a professional opinion. They can determine the best location for your thermostat.

If you need HVAC assistance, we recommend calling a licensed heating and air conditioning professional so you can get the most comfortable and efficient use of your furnace!