How To Fix Furnace Short Cycling

Furnace sWhen a furnace short cycles, it turns off before reaching the desired temperature, or it turns off and on too often. It isn't usually dangerous to you or your health, but if not addressed quickly, it can be detrimental to your furnace. To help you prevent damage to your system, we have compiled a list of factors that may be responsible for your furnace short cycling problems.

Why Is My Furnace Performing Short Heating Cycles?
- 1.) The Furnace is Too Large
- 2.) Clogged Exhaust Vent
- 3.) Damaged Flame Sensor
- 4.) Contaminated Air Filters
- 5.) Heat Vents are Shut
Length of a Heating Cycle
How Many Times Does a Furnace Operate Per Hour?
Negative Effects of Furnace Short Cycling

Why Is My Furnace Performing Short Heating Cycles?

1.) The Furnace is Too Large

When it comes to furnace size, bigger is not necessarily better. A furnace needs to be the proper size for a house or else there will be erratic heating cycles and temperature changes. If your furnace is turning on for only 3-7 minutes at a time, it's probably a larger-than-needed furnace. Your house will be freezing one moment, toasty the next, and then back to freezing. This can alter a heating bill to be higher than expected.

2.) Clogged Exhaust Vent

If your furnace is turning on for only 1-5 minutes at a time, chances are it's a clogged exhaust vent. This can pose a potential threat to the safety of your home: with a blocked vent, carbon monoxide has nowhere to go and can leak out of the furnace and into your home. Common causes of a clogged exhaust vent include bird or animal nests, beehives, or an abundance of ice or snow.

3.) Damaged Flame Sensor

Flame sensors, also known as flame rods, work by detecting the presence of a flame in the furnace. It is a short, thin metallic rod that creates a small current in order to confirm that there is a fire burning in the furnace. If your flame sensor is faulty, your furnace will constantly cycle on and off. It will shut off almost as soon as it lights. Your furnace turning on for only seconds at a time is probably due to a damaged flame sensor. This is one of the more common causes of short cycling. Sometimes, all you need to do is clean the flame sensor and your furnace should be back to normal. If that doesn't work, then it's probably time to call a professional.

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4.) Contaminated Air Filters

For furnaces that are only turning on 2-5 minutes at a time, the solution could be to change your furnace filter. Dirty furnace filters can cause an overheated furnace which will then shut off before the house is warm. Another tip to tell that the filter is the issue is if the air blowing when you turn the heater on is hotter than usual. Simply clean or replace the filter if this is the issue.

5.) Heat Vents are Shut

Similarly, closed heat vents will also overheat a furnace. While a contaminated air filter doesn't let enough air in, heat vents that are shut do not let the air out. If your furnace runs every 5 minutes, then this could be the problem. This has an easy fix—simply ensure that 75% of your heat grates' dampers (the vents in each room) are open.

Length of a Heating Cycle

A furnace cycle is when a furnace turns on to heat up the house then turns off once the desired temperature is achieved. The length of your furnace's heating cycle depends on how cold it is outside. The colder it is, the longer the length of the cycle. Heating cycles may be anywhere from 10-15 minutes.

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How Many Times Does a Furnace Operate Per Hour?

Functioning correctly, a furnace should go through about 2 to 3 cycles per hour. Typically, furnace cycles tend to be long in order to properly heat a house and keep it warm.

Negative Effects of Furnace Short Cycling

Short cycling prevents a furnace from heating up a home the way it is supposed to. Furnaces need to complete their full cycles to function, so if anything is countering a furnace's efficiency, your home will not get warm. A short cycling furnace can have more serious effects, however. It wears down all the parts of a furnace at an increased rate. This means that your furnace could have more problems and require more maintenance in the long-run. The longer a heating system goes short cycling, the shorter the furnace lifespan gets.

Because of the various complications furnace short cycling causes, it's best to reach out to licensed, professional technicians. Our staff offers any kind of furnace service you might need—repair, maintenance, or installation. Give the guys in the big orange trucks a call at (732) 201-3305 to receive dependable HVAC repair solutions. Your home will be warm and toasty in no time!

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