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Why Your Furnace Is Running Constantly: Common Causes and Solutions

November 13, 2023

Does your furnace seem to be running constantly? A constantly running furnace or one that short cycles is a common issue for homeowners. This can create higher energy bills and cause unnecessary wear and tear on your HVAC system. 

Sometimes it is a simple fix, however, it can also mean that there is a potential issue with your furnace. 

In this blog, we'll explore the common reasons why a furnace may run constantly and offer solutions to help you solve the problem.

 

Constantly running vs short cycling

Before we dive into the reasons a furnace may run constantly, it’s good to distinguish between a furnace that runs constantly even after reaching temperature vs one that is short cycling. 

Short cycling occurs when an HVAC system turns on and off too often. This can make it appear as though the furnace is constantly running when it is actually just turning on and off way too often. 

Both may indicate a problem with the furnace, but understanding the difference can help to diagnose the real issue. 

 

7 reasons your furnace may be constantly running (or short cycling)

 

1. The thermostat is incorrectly set 

The thermostat is where many HVAC issues begin. When it comes to a constantly running furnace, the culprit could be the fan setting. If set to “run” rather than “auto” your fan may continue to blow constantly. 

You may also want to check the batteries. Sometimes as thermostat batteries die, the thermostat can act up, even if it lights up when touched. 

 

2. The thermostat is in a bad Location

The location of your thermostat can affect its accuracy. A thermostat installed in a cold area of the home or near a drafty entrance may not accurately reflect the temperature in the rest of your home. This can cause your furnace to run constantly to compensate for the discrepancy. 

Relocating your thermostat to a more representative area can help maintain a more consistent temperature.

 

3. Rooms are poorly insulated

A poorly insulated home with drafts and air leaks can prevent your home from reaching the desired room temperature causing your furnace to run continually. It can also lead to rooms cooling down too quickly causing the furnace to turn on shortly after turning off making it appear as if it is constantly running.

To combat this problem, consider sealing any gaps, insulating your home, and investing in weatherstripping for doors and windows.

 

4. The air filter is clogged

Dirty or clogged air filters restrict the airflow in your HVAC system, forcing it to work harder to circulate warm air. Regularly changing or cleaning your furnace's air filters is essential for maintaining proper airflow and efficiency. Aim to replace or clean your filters every 1-3 months, depending on your specific system and usage.

 

5. The temperature is set too high
Similar to having a poorly insulated home, having a temperature set too high could lead to a furnace constantly running or turning back on shortly after turning off. This is especially common during extremely cold weather. 

The higher the temperature is set, the more you can likely expect your furnace to run. This is especially true for poorly insulated homes and ones in which a furnace is too small. 

 

6. Your furnace is the wrong size

Sometimes, the furnace itself may be the problem. An oversized furnace can lead to short cycling, where it heats the space too quickly and shuts off. And a furnace that is too small will struggle to adequately heat the home causing it to constantly run.  

In Maryland, it’s recommended that a furnace generates 40-45 BTUs per square foot of a home. Take a look at your furnace's BTU rating and compare it with the size of your home to see if this could be a reason for your heating issues.  

 

7. The furnace is breaking down or has malfunctioning components

If your furnace is old or has not been properly maintained, various components may wear out or fail, causing the system to run continuously. Common issues include a malfunctioning blower motor, a faulty ignition system, or a dirty burner.

 

Fixing Your Furnace

A furnace that runs constantly is not only an inconvenience but can also lead to increased energy bills and potential long-term damage to your HVAC system. If you are experiencing this then it’s best to address the issue immediately. 

First, do all that you can do as a homeowner. Check your thermostat, change the batteries, ensure your rooms are properly insulated and the cracks in your doors and windows are properly sealed. You will also want to make sure you have a clean air filter and that it is facing the right way. 

If these issues are not the source of the problem, we recommend calling an HVAC professional to diagnose the issue. Attempting to fix a furnace problem without technical knowledge can cause further damage to the HVAC system.   

Regular maintenance and timely repairs are key to keeping your furnace in top condition, so don't hesitate to consult a professional if you suspect any problems with your heating system. With a well-maintained furnace, you can enjoy a cozy, worry-free winter season.

Is HVAC maintenance really necessary? Is it worth hiring an HVAC company to do it? We show you what maintenance can do to help you decide whether it's worth it for you.