How To Tell If Your Furnace Is Short-Cycling

wrapped in blankets due to malfunctioning heating system

Winter is in the air. You can already feel the heat subsiding and the cold breeze blowing. Soon the temperature will drop to uncomfortable levels. Make sure that you and your family will be spared from freezing nights. Check your furnace this early to see if it is working as it should. Some issues can be fixed in a snap while others are not as easy. For example, short-cycling is a major concern that merits professional attention. When a furnace short cycles, the furnace runs then shuts off and starts again repeatedly.

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How Can I Tell If My Furnace Is Short Cycling?

A normal furnace will turn on and run continuously until it reaches the desired temperature. Then it will turn off and allow the space to maintain that level of heat. It will take a while before it needs to turn on again due to falling temperatures. On the other hand, a short-cycling furnace will turn on and turn off again in quick succession. It will not reach the thermostat setting. It will simply shut down and run again causing wear and tear on the system. Although the furnace is running, the house will feel cold throughout the day.

Why Does A Furnace Short Cycle?

image of question marks depicting furnace short cycling question

This situation cannot persist. It wastes energy and causes component damage while allowing the house to grow cold. If you notice this problem, then move quickly to resolve it. The right solution will depend on the actual cause. Below are a few of things that can trigger this erratic behavior:

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1. Your Furnace is Overheating

HVAC systems have built-in protection from damage. Although the job of a furnace is to heat up the house, there is such a thing as the unit getting too hot. It can detect if it has crossed a dangerous level and turn itself off right away. It needs to take this emergency measure to prevent damage such as the development of cracks in the heat exchanger. Lethal carbon monoxide can leak from such cracks so you should be thankful that it stopped when it did. Overheating can usually be traced to airflow restrictions from blocked exhaust vents and dirty air filters.

2. Having A Bad Flame Sensor

malfunctioning flame sensor on furnace

If your furnace has a bad flame sensor, then you can expect the flame to shut off as soon as it lights. You need to understand that the sensor is there to monitor the gas valve. It is a safety mechanism that prevents raw gas from getting into the home. It shuts the valve off when there is no flame. When sensors malfunction, they shut off the gas valve even when it is actually necessary. Cleaning the sensor might fix the problem. If not, then it will have to be replaced. Get an HVAC technician to do this for you.

3. The Heat Grates Are Blocked

The job of the furnace is to heat up air and push this out to the grates. If hot air can’t flow freely out of these heat grates, then the heat will be trapped inside and cause the system to overheat. We will have another episode of short-cycling unless the underlying issue is resolved. Understand that the grates have control mechanisms called dampers that let house occupants control whether a room gets heated or not. This is useful for saving energy. However, a high number of closed vents might lead to overheating. Keep 75% of these open at all times.

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4. Your Furnace Filter Is Dirty

replacing furnace filter

Short-cycling can be the result of a dirty filter. Unlike faulty flame sensors that result in immediate shut-off, dirty filters will allow the furnace to run for a few minutes before shutting down. You might also notice that the heat grates are pumping out hotter air than what you’re used to. When the filter gets dirty, air cannot flow back to the furnace to cool it down. The heat will simply build up to unmanageable levels. It will then automatically shut down as a safety precaution. If the filter is washable, then clean it. If it is disposable, then replace it.

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5. The Exhaust Vent Is Blocked

Exhaust vents should always remain open. However, there are cases wherein vents get blocked due to vegetation, snow, nests, beehives, and so on. All obstructions must be removed as soon as possible. In fact, this should be checked regularly as part of maintenance. Sometimes it can get tricky such as if a dangerous animal is blocking the openings. In this situation, it is prudent to call animal control rather than expose yourself to harm.

6. Your Thermostat In The Wrong Spot In Your Home

image of a thermostat in a poor location

The thermostat has sensors that gauge indoor temperature. It regulates furnace activity in response to what it senses in its environment. However, it might not be able to do its job properly if it is located in the wrong spot. For instance, if you put it near a window, a heating grate, or any other hot spot, then it will have skewed sensor readings. The thermostat will think that the house is already hot and shut the system down prematurely. Take it to a neutral location away from anything that could grossly influence its temperature readings.

7. Your Furnace Is Too Large For Your Home

It is tempting to get a large furnace when we want to feel secure about the capabilities of our heating system. However, bigger isn’t always better. When it comes to furnaces, excess capacity can be detrimental as it causes short-cycling. The components will wear down faster, the temperature swings will be more pronounced, and the heating bills will be higher than usual. The sensible, yet costly solution. is to replace the unit with a furnace of the correct size. An experienced HVAC contractor can perform precise calculations.



Make your home comfortable this winter by addressing any furnace issues early. If you notice short-cycling, then determine the cause based on the clues provided above. Get help from an expert HVAC technician for proper diagnosis and replacements. Your diligence will be rewarded with a stress-free winter and a longer-lasting heating system.

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McAllister EnergyMcAllister Energy offers superior heating and cooling services in Camden County, New Jersey. We hire the best-certified technicians who can provide you with excellent HVAC tune-ups, repairs, installations, and replacements. Each of our techs has the knowledge and experience to service your HVAC system correctly.

McAllister Energy guarantees the most competitive heating and cooling service costs in the area. Our HVAC maintenance services can improve your comfort, increase your energy efficiency while reducing your home cooling costs. If you happen to need an HVAC repair or replacement system, we can recommend the best one for your home while staying within your budget. We back all of our work with a guarantee to ensure your satisfaction. To schedule a service appointment, give McAllister Energy a call today. We offer free, in-home estimates.

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