Furnace Short-Cycling: Causes & Solutions

image of girl with blanket due to furnace short cycling

You can feel the advance of winter in the air. The cold, crisp breeze and the gradually subsiding of the summer’s heat are already noticeable. Soon, outside temperatures will plummet to levels that are downright uncomfortable. Now is the time to ensure that you and everyone in your home can avoid the discomfort and danger of freezing nights. Inspect your furnace early-on to verify that it’s functioning properly. Some furnace issues can be quickly and easily resolved while others are far more complex. For instance, issues with short cycling are a major concern and one that warrants a professional inspection. When your furnace is short cycling, you will notice that the furnace runs then shuts off and starts again repeatedly.

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Signs That Your Furnace Is Short Cycling

When a furnace is functioning normally, it will turn on and stay on until the desired temperature has been reached. Once it has, the furnace will shut off so that the indoor area can maintain the desired temperature. The furnace will not turn on again for quite some time until temperatures within the space drop. Conversely, a furnace that’s short cycling will turn itself off and on in quick cycles of operation. It won’t have the ability to create the desired temperature inside the home. Instead, it will turn off and on, causing expedited wear to the heating equipment. Even though the furnace is still essentially running, the interior of the home will constantly feel cold.

What Causes Furnace Short Cycling?

image of question mark depicting why heating short cycles

Short cycling is not an issue that you can afford to neglect. It results in a tremendous waste of energy. It can leave your house cold, and it can result in major damage to various HVAC components. If you notice your furnace short cycling, you have to take fast action. The best solution will depend upon the underlying cause. Following are a few things that might cause your furnace to perform in this erratic and incredibly frustrating way:

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1. The Furnace Is Overheating

HVAC systems have protection against certain forms of damage built right into them. Even though a furnace is designed to warm up the house, these units are actually able to overheat. A furnace can detect when a dangerous level of heat has been reached and it will turn itself off immediately. It takes this measure to prevent further damage like the development of a cracked heat exchanger. When the heat exchanger has a crack, lethal carbon monoxide gas can leak out into the home, and thus, you should be grateful that the unit turned itself off. Overheating is often the result of restricted airflow which might be caused by a dirty air filter or a blocked exhaust vent.

2. The Flame Sensor Is Damaged

gas furnace flames

If the flame sensor in your furnace is damaged or no longer working, the flame will turn off right after it lights. It’s important to note that the sensor exists to monitor the gas valve. This safety mechanism is designed to prevent raw gas from entering the living environment. It shuts off the valve whenever the flame is out. Whenever a sensor malfunctions, they turn of the gas valve even when this valve is needed. One way to fix this issue might be to clean the sensor. However, if this doesn’t do the job the sensor may need to be replaced. This is something that a licensed HVAC technician can take care of.

3. Your Furnace Has A Dirty HVAC Air Filter

image of a dirty furnace filter

Having a dirty air filter in your furnace can cause short cycling. While a faulty flame sensor will lead to an immediate shut-off, a dirty filter will allow your furnace to run for several minutes and then shut down. You might notice that the air being pumped out of the heat grates is significantly hotter than normal. When the filter is clogged and dirt, air is unable to flow back into the furnace for cooling. This causes the heat to build to a level that eventually become unmanageable. As a safety precaution, the furnace will shut itself down. If the filter can be washed, you will need to clean it. If the air filter in your furnace is disposable instead, replace this component right away.

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4. One Or More Heat Grates Are Blocked

image of hvac air vent

A furnace has the task of warming air up and then pushing it out through the heat grates. If hot air is unable to freely flow from the heat grates, then it will remain trapped inside until the furnace overheats. Until the problem is taken care of, short cycling will continue to occur. Keep in mind that there are control mechanisms on the grates known as dampers that those within the building can use to allow heat into a room or keep it out. This is one way to save energy. However, if too many grates are closed at one time, this can result in overheating. Try to keep at least 75 percent of the dampers open at all times.

5. There’s A Blockage In The Exhaust Vent

An exhaust vent should never be closed. There are, however, times when these vents might get blocked by snow, vegetation, beehives, nests, and other such things. Any obstruction should be removed right away. In fact, you should routinely check for instructions as part of your ongoing maintenance and care. Keeping the exhaust vent open can sometimes be a challenge such as when dangerous animals block these openings. If this ever occurs, get in touch with animal control services rather than taking on the risk of resolving the problem alone.

6. Your Thermostat Is Installed In A Less Than Ideal Spot

hand increasing heating temperature at home

Thermostats have sensors that read the temperature indoors. Your thermostat is designed to regulate the activity of your furnace based on what it detects in the environment. This component, however, may be unable to do its job well if it’s been installed in a less than ideal location. For example, if it’s positioned near a heat grate, window, or any other spot with secondary heat, then its sensor readings will be skewed. The thermostat will consider the house as being hot already and will therefore prematurely shut the system down. Have this installed in a more neutral location where it is away from anything that might impact its ability to read the indoor temperature correctly.

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7. Your Furnace Is Too Big For Your Home

When you want a highly capable home heating system, you may be tempted to invest in the biggest furnace you can find. Bigger, however, doesn’t always mean better. Excess capacity for a furnace can be problematic given that it can lead to short cycling. The furnace components will be subject to expedited wear, there will be more pronounced temperature swings throughout the building, and your heating bills will be unnecessarily high. A far more cost-effective and sensible solution is to have a proper-sized furnace installed. This can be done with the help of a seasoned HVAC contractor who can perform accurate furnace size calculations.

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Deal with furnace issues early-on to make your home more comfortable this winter. If short cycling is a problem, find out what the cause is by using the clues above. Get in touch with an HVAC expert for accurate diagnosis and timely repairs or replacements. You’ll be rewarded for your diligence with a stress-free winter and a heating system that actually lasts.

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