Reasons Why Your Heater Might Short Cycle

January 20, 2023


Heater short cycling is one of the most frequent heating repairs that professional HVAC contractors are asked about during the winter season. Short cycling is when a furnace, heat pump, or ductless heating and cooling system abruptly starts and stops working. When a heating system has “short cycles,” it means that it runs for a short while before turning off, usually before reaching the temperature you’ve set on the thermostat.

If your heater runs in short bursts throughout the day, your energy costs could increase, your home might not be heated evenly, and wear and tear on your heater could happen more quickly. In this blog, we’ll explain what short cycling is, why it matters, the typical causes of this problem, and what you should do to fix it if your system exhibits this fault.

What Is Heater Short Cycling?

A system’s “cycle” in the HVAC industry refers to the time it runs before turning off automatically. Normal heating and cooling system operations will continue until the home’s temperature has been sufficiently changed. In a typical situation, a furnace or heat pump cycles several times an hour, returning when the house temperature drops.

As the name implies, “short cycling” refers to a malfunction where the system’s runtimes are extremely short, causing the system to turn on and off frequently. The system rarely operates during a short cycle for more than a few minutes at a time. You’ll likely hear the system turning on and off more than a dozen times in an hour if you pay attention to its sound.

What Leads To Short Cycling?

The three most common causes of furnace or heat pump cycling are improper sizing, thermostat issues, and inadequate insulation. What you need to understand about all three is as follows:

Improper Sizing And Installation

Most unconsciously believe that bigger is better when it comes to HVAC systems. On the surface, it’s understandable why the majority of homeowners believe that a furnace or heat pump with a higher capacity will heat their home more quickly and efficiently. But that isn’t how it works. Short cycling is one of the performance and efficiency issues that can result from a system that is too big for your house.

When operating normally, all heating and cooling systems perform at their peak efficiency, preventing the need for HVAC maintenance and repair services. This is difficult for a system that is too big for your house. It will turn on, run, and quickly increase the temperature inside. To keep the temperature constant, the larger furnace will run numerous short cycles throughout the hour, wasting a lot of energy.

Thermostat Issues

A broken thermostat can also bring on short cycling issues. Depending on the temperature inside, the thermostat will tell your furnace or heat pump when to run. However, faulty wiring in the thermostat can frequently result in the wrong instructions being sent to the system, which will cause the heater to repeatedly turn on and off without running continuously.

You should call a licensed HVAC expert to your home to inspect the thermostat and its wiring if you think it could be the source of your short cycling problems. The technician can at least eliminate it as the cause if the thermostat is not the problem before moving on to look into other potential issues.

Inadequate Airflow And Insulation

Try cleaning the air filter before moving on to your furnace. A clogged air filter could cut off the system’s airflow, which could cause several performance issues, including problems with cycling. Another potential issue that you should look into with the assistance of your HVAC expert is inadequate insulation.

If your house has significant air leaks, inadequate attic or wall insulation, or leaky ducts, your heating system is more likely to short cycle. Every home loses some of the heat it generates, but poorly insulated homes will lose their heat at such a rapid rate that the furnace will constantly be trying to catch up.

About Nor-Can Heating & Air

Nor-Can Heating & Air is an HVAC installation, maintenance, and repair company based in Edmonton. At Nor-Can Heating & Air, our expert HVAC technicians maintain, repair, and install air conditioning, heating, and ventilation units. We also provide trustworthy humidifier repair and replacement services for all brands and models. Learn more about Nor-Can Heating & Air and our services.

Considering investing in a reliable heating system for your house? Contact us now.


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