Reasons Why Your Furnace is Short Cycling

Short cycling furnaces can be a real drag—literally! If you’re the owner of a short cycling furnace, you know…

Short cycling furnaces can be a real drag—literally! If you’re the owner of a short cycling furnace, you know how frustrating it can be. You’re left with inconsistent temperatures, high energy bills, and an unreliable system. Short cycling occurs when your furnace turns on and off more frequently than it should. It’s usually a sign of an underlying problem, and it’s essential to have your furnace checked by a professional. In the meantime, here are some of the issues that can cause short cycling, and how to address them.

Your furnace is incorrectly sized.


Incorrectly sized furnaces are one of the primary reasons why a furnace may be short cycling. When a furnace is too small for the space it’s attempting to heat, it will struggle to adequately warm up the area and will run more frequently than necessary in an attempt to reach the desired temperature. This causes rapid on/off cycles which can cause wear and tear on components as well as reduce energy efficiency. In addition, because this type of short cycling does not allow enough time for air within the ducts to completely change out, stale air can remain within the system leading to poor indoor air quality. Incorrectly sized furnaces also tend to overheat due to their inability to properly cycle off before reaching maximum capacity. A good rule of thumb when selecting a new or replacement furnace is that you should select one with 10-15% greater capacity than what is needed for your specific space in order to ensure its longevity and reliability while still keeping operating costs reasonable.

Your furnace has a failed blower motor or fan limit switch.

A failed blower motor or fan limit switch is one of the most common reasons why a furnace may be short cycling. The blower motor, also known as an inducer motor, is responsible for circulating air throughout the system and through your home. The fan limit switch acts as a safety by turning off the burner if it senses that either too much heat has built up in the system or not enough airflow is taking place to cool down the furnace’s components. When either of these parts fails, they can cause abnormal operation with your heating system resulting in short cycling. If you are experiencing this issue, it’s best to have a professional check both components to identify which one needs replacing before any damage occurs from overheating due to improper airflow.

Your furnace has heat exchanger issues.


If you’ve noticed that your furnace is short cycling, one of the possible reasons could be that your furnace has heat exchanger issues. A heat exchanger is an essential component of your furnace, and it’s responsible for transferring heat from the burning fuel to your home’s air. If the heat exchanger malfunctions or becomes blocked, it can lead to short cycling, where your furnace repeatedly turns on and off without completing a full cycle.

Your furnace has a clogged air filter.

When your furnace is short cycling, it may be a sign that something is not quite right. One of the most common causes of this problem is a clogged air filter. An air filter is an important part of your furnace, as it helps to keep dust, dirt, and other debris from entering the system. If the air filter becomes too clogged, it will restrict the airflow, causing your furnace to cycle on and off more frequently than it should. If your furnace is short cycling, you should check the air filter first to see if it is clogged and needs to be changed. Most air filters need to be changed every three months or so, depending on the type of filter and the type of furnace you have. If you don’t know how often to change your air filter, check your furnace’s operating manual or ask a professional.

Overall, understanding the reasons why your furnace is short cycling is essential in order to ensure your furnace is running efficiently and safely. Taking the time to troubleshoot and identify any underlying issues will help prevent costly repairs or replacements in the future. When your furnace does start short cycling, the best option is to call an HVAC technician to resolve the issue.