AC Repair: Understanding the Short Cycle
During normal operations, you should hear your furnace complete 2 or 3 heating cycles per hour, with each cycle lasting approximately 10 to 15 minutes. During extremely cold days or if a home is poorly insulated, heating cycles may be slightly more frequent or last a little longer. However, if heating cycles come very quickly and end just as quickly, this is a condition called “short cycle.”
A short cycle happens when the furnace heats the home successfully, reaching the temperature setting indicated by the thermostat. However, the cycle ends before the air has time to mix and circulate, so rooms that are the most distant from the thermostat are still cold. The cold air forces the thermostat to call for another heating cycle, which, again, ends too soon.
4 Hidden Reasons Your Furnace Will Short Cycle
Short cycles indicate one of several underlying problems that need to be addressed. They include:
A Wrong-sized Furnace. Before a furnace is installed, a technician completes a J-Load calculation, measuring the square footage, insulation value, window and door openings, and other factors about the home that affect heating and cooling. The calculation indicates the proper size furnace, measured in BTU output. A system too small will struggle to keep a home warm with “long cycles,” and a system too large will cause “short cycles.” Both cause furnaces (and air conditioners) to run inefficiently and wear out too quickly.
A Dirty Air Filter. The furnace is working to create sufficient warm air to make a home comfortable. But a dirty filter will reduce the airflow needed to move the heat throughout the home. Dust and other airborne particles collect on the surface of the filter until the filter is completely covered. For this reason, an air filter needs to be changed about every three months (more often if needed).
Thermostat Malfunctions. A properly placed thermostat will be installed on an inside wall, and out of direct sunlight. It functions best when placed in a central spot in the home. If the thermostat is improperly placed, it should be moved. Thermostats are battery-powered, so remember to change the battery annually. Occasionally, thermostats experience wear and need to be recalibrated. A malfunctioning thermostat will cause a furnace system to have short cycles.
Malfunctioning System. An aging or worn furnace may experience electrical or mechanical problems that create the conditions for short cycles. A heat pump that loses refrigerant will also lose the ability to collect heat from outdoors: the blower motor will continue to blow, but the heat will be missing from the coil. Wear can also affect sensors and control mechanisms, including capacitors and control boards (small computers).
If your furnace system begins to exhibit any short cycle tendencies, try these tasks in this order.
- Purchase a supply of air filters and change the filter. Observe the furnace to determine whether the short cycles have ended. Make sure to change the air filter regularly.
- Check the thermostat settings. Ensure that it is on HEAT or EM/AUX HEAT and that the temperature setting is at least 5 degrees lower than the temperature indicated on the thermostat face.
- If the settings are correct, turn the thermostat OFF temporarily and change the battery (or batteries). Observe to see whether the short cycling has ended.
- Check the vents and registers around the home. Make sure all are uncovered, since covered vents will reduce circulation.
- If short cycles continue, call your furnace/air conditioner technician for maintenance and repair.
Stop the Short Cycle Today
If your system is trapped in a persistent short cycle, ignoring the problem can lead to sky-high energy bills and premature equipment failure. These rapid bursts of activity put unnecessary strain on your HVAC components, often indicating a deeper issue like a faulty sensor or an improperly sized unit. Our professional technicians have the tools and experience to diagnose your system and restore perfectly balanced comfort to every room in your home. Call All Cool AC & Heating today at 281-238-9292 to schedule your AC maintenance appointment and get your system back on track.


– Take a look at your thermostat. Is it outdated? Many of the newer thermostat model are more energy efficient and can reduce your utility bill. Check out programmable thermostats and smart thermostats. Each can offer some great energy saving and convenience opportunities.