5 Reasons why your furnace is short cycling

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. Here are five reasons why your furnace might be short cycling, and what you can do about it.

1. Dirty filters

Located on ceilings and walls throughout the home, an air filter serves two important purposes. One, to keep the HVAC system clean, and two, to keep airborne contaminants from polluting the air in your home. Air filters keep the HVAC system clean and free from dirt and dust through trapping these particles before they can reach the system. This allows the system to maintain its efficiency, saving you money on your energy bills in the process.

Dirty filters physically block warm air from entering your home. This means that your heater may be doing its job, but if your filters are dirty, the warm air won’t make it past the vents. All you have to do is replace your filters to restore the flow of warm air.

How often should you replace your filters? The answer depends on where your home is, how many people live there, and if you have any pets. A home with three dogs in an urban area is going to need its filters changed more often than a home with no pets in a rural area. The following can be used as general guidelines for filter replacement:

  • Vacation or seasonal home: every 6 months
  • Home without pets: every 90 days
  • Home with pets: every 60 days
  • Home where one or more people have allergies: every 30 days
  • Home in an area with bad air pollution (including dust from desert monsoon storms): every 30 days

Furnace filter

Along with the filters located in your home, your furnace uses a dedicated filter to prevent contaminants from invading the core of the system. Depending on your furnace model, you’ll find your filter either just inside the furnace or inside the return vent. Start by removing your current filter. You can use this to help you determine exactly what size and type of replacement filter you need. Once you have a replacement, use the arrows on the side of the filter to indicate which direction it should be installed. Installing a filter the wrong way can impede airflow, further compromising your furnace’s efficiency.

While it’s common to only change a furnace filter once a year, you can keep your furnace running at its best by changing the filter more frequently. Make a habit of checking the filter every month or so to see if it’s ready to be replaced. You’ll know it’s time for a new filter if the current one appears visibly dirty or clogged with dusty debris.

2. Overheating

Your furnace includes safety features that allow it to shut off when the system overheats. This automatic shutoff can be triggered by internal problems, such as a blocked heat register, malfunctioning blower motor, or a faulty limit switch. Work with an HVAC professional to diagnose the exact reason why your furnace may be overheating.

3. Oversized furnace

When it comes to furnaces, bigger isn’t always better. If your furnace is too large for your home, it will almost inevitably short cycle. This can lead to uneven heating and higher energy usage. If you suspect your furnace is too large for your home, replacing it with a system that is the correct size can save you money in the long run. Experienced HVAC professionals use specific metrics and measurements to ensure your furnace is the proper size for your home.

4. Insufficient maintenance

Your HVAC system needs to be professionally inspected at least twice a year to ensure that it stays at peak performance. An appointment in the spring can prepare your air conditioner for the upcoming summer, while an appointment in the fall can get your furnace ready for the winter ahead. With two annual maintenance appointments, any small problems can be caught and fixed before they develop into larger and more expensive ones.

5. Thermostat issues

If your thermostat isn’t working right, your furnace won’t work right either. A malfunctioning thermostat can lead to short cycling, no heat, and rooms that never quite feel warm enough. That’s why it’s important to address common thermostat problems before they turn into big, and expensive, headaches.

Power and batteries

If your furnace is short cycling, and you believe your thermostat is to blame, make sure it’s on and set to “heat”, not “cool.” Simple as it may seem, you’d be surprised how often professionals are called out to fix a heater when the only problem is that it’s not turned on. Then, check to see if the batteries need replacing. A low battery indicator will display on the thermostat’s screen to let you know when it’s time to replace them, but this can be overlooked.

If you’re unsure of how to replace your thermostat batteries, consult your owner’s manual for instructions specifically tailored to your model. In general, to replace your thermostat batteries in a thermostat that does not have an external battery compartment, you’ll follow these steps:

  • Pull the thermostat box off its wall-mounted plate.
  • Turn the box over and use a small screwdriver to open the battery slot.
  • Discard the old batteries and replace them with new ones, then close the battery slot.
  • Put the thermostat box back onto the wall mount and slide it down until you hear it snap or click back in place.

If your thermostat has an external battery compartment, press down on the top right corner of the thermostat to reveal the compartment. Then, remove the compartment to replace the batteries before snapping it back into place.

Thermostat calibration

If your thermostat isn’t reading the temperature of the room completely, it won’t send the right signals to your furnace. This leads to rooms that feel too cold, or too hot, for comfort. The way to fix this is by recalibrating the thermostat. But first, you’ll need to verify that it needs to be recalibrated.

To do this, you’ll need the following:

  • Glass tube thermometer
  • Tape
  • Paper towel

Start by taping the glass tube thermometer to the wall, a few inches away from your thermostat. You don’t want the thermometer to directly touch the wall, so pad it with a paper towel. Turn your thermostat on and wait 15 minutes before comparing temperature readings.

If the difference between what your thermostat says and what the thermometer says is more than a degree, your thermostat may need to be recalibrated. This is usually done as part of annual heater maintenance, but you can have it done at any point in the heating season.

Stay warm with Chas Roberts

If furnace problems have you shivering long into the night, turn to the experts at Chas Roberts. From routine repairs and annual maintenance to HVAC emergencies and system replacements, there’s no problem our pros can’t solve. Contact us to get started.