Periodically, your furnace will turn on to reach a desired temperature before shutting off. This is called cycling, and the frequency in which it occurs depends on a few factors.
The average number of cycles your furnace will perform in an hour is 2-3, though winter temperatures could increase this number upwards of 3-10.
Again, how often is dependent on the thermostat, your preferences, and a malfunction known as short cycling.
Table of Contents
- Thermostat Setting
- Winter Temperatures
- What about the Cost?
- Suggestions to Reduce the Bill
- My Furnace Cycles More than Average
- What is Short Cycling?
- Routine Maintenance
- Possible Causes of Short Cycling
- Check the Air Filter
- Make Sure All Vents Are Open
- The Exhaust Vent Might Be Blocked
- Your Thermostat is Broken
- Where is the Thermostat?
- The Furnace is the Wrong Size
- The Flame Sensor Could Be Damaged
- Related Questions
- How much is it to replace my furnace?
- Can I fix the Furnace Myself?
How often your furnace cycles heavily rests on what you set the temperature to on the thermostat. The most efficient use is to set a lower temperature in cool weather and a higher temperature in heat.
However, each person has their own comfort levels, so your furnace would cycle more often if you set the opposite.
How often your furnace will cycle in the winter depends on you. If you enjoy the cold, you’ll likely set your thermostat lower and the furnace will only turn on, at most, 3 times an hour.
On the other hand, if you can’t handle cold temperatures at all and need the house to feel like a sleeping bag, your furnace will probably cycle on the higher side of things.
What about the Cost?
In case you’re concerned about the gas bill and wonder how the thermostat setting will affect the bottom line, the answer basically comes down to how hot or cold you want to be.
Keep in mind that your furnace uses much more gas every time it starts up and shuts off than it does to run continuously, so the number of cycles will increase or decrease the gas bill.
Suggestions to Reduce the Bill
To control the cost of your furnace, there are a few things you can do. One is to follow the idea above and set the thermostat lower in cold temperatures and higher when it’s a hot day.
If the house will be empty during a certain period of time, say your 9 to 5 job, you can set a drastically high or low temperature until you’re home.
My Furnace Cycles More than Average
There is a malfunction in furnaces called “short cycling,” which is bad for a number of reasons and needs to be fixed.
What is Short Cycling?
Your furnace “short cycles” if it shuts on and off too often or never reaches the temperature set on your thermostat. This can cause stress and wear out your furnace quicker, and it will take a toll on your wallet.
While short cycling may require a technician to fix it or a replacement of the unit, there are a few things you can do before doing either step.
One basic principle is to have your furnace serviced twice a year to fix small issues before they graduate to bigger problems. This is preventative and will make sure your furnace operates at maximum efficiency.
Possible Causes of Short Cycling
Despite it being cold in the winter, your furnace is most likely to overheat during this time. This is because your furnace has a heat exchanger, which is responsible for heating the air.
If your heat exchanger is being overworked, which can happen from your furnace short cycling, it will overheat and potentially ruin the part.
Causes of Overheating: There are a few different reasons that your furnace might overheat, but the good news is that most of them are avoidable.
Check the Air Filter
One major cause of overheating is a dirty air filter. This prevents air from entering the furnace, which doesn’t let the heat exchanger cool down.
The air filter in a furnace should be replaced about every 90 days in an average home. If you have pets or some form of allergy, that time drops to every 60 days.
Either way, a clean air filter is imperative to keep your furnace operating efficiently.
Keep the Blower Wheel Clean: The blower wheel keeps the air circulating in your furnace. If dirt clings to it, the part could become less effective or fail entirely, resulting in an expensive repair.
The easiest prevention for this is to continuously replace your air filter and maintain a clean furnace.
Make Sure All Vents Are Open
Air flow is obviously extremely important to a functioning furnace. Make sure to keep all air vents open in your home, even in rooms you don’t use.
Without proper air circulating to the heat exchanger, the heat will build up and cause the furnace to short cycle.
The Exhaust Vent Might Be Blocked
Your furnace has an exhaust vent, the flue pipe. If this vent is blocked in any way, you’re at risk of carbon monoxide poisoning, which can be fatal.
If you check every option and your furnace is still not operating fully, or if you smell gas coming from your ventilation, it’s best to call a maintenance technician to check the flue pipe.
Your Thermostat is Broken
The thermostat controls what temperature your air is, and whether the furnace turns on at all. A faulty thermostat will make your furnace short cycle.
There are a few reasons that your thermostat might be the reason for short cycling.
Low Battery: The most obvious way to know if your thermostat is malfunctioning is to check if it needs new batteries.
If the screen is blank or has a flashing symbol, it may just need the batteries replaced. If that doesn’t work and the thermostat still seems to be broken, it may need repaired by a professional.
Faulty Wiring: Another possibility is that the wires connecting to the thermostat are failing, whether from being put in wrong or just being old.
If new batteries don’t fix the thermostat, a technician may need to check your wiring.
Where is the Thermostat?
If your thermostat is located near an operating heat source, it could affect the temperature reading and cause your furnace to short cycle.
The best possible fix is to move whatever the heat source is. If this isn’t possible, contact a professional to rewire the thermostat to a different area of your home.
The Furnace is the Wrong Size
If your furnace is too big for the house, it will heat the space too quickly and shut off, causing it to short cycle and damaging the furnace.
This is most likely caused by the installers not performing a calculation known as a manual J heat load, which tells the proper size furnace for your home.
To fix this, contact a professional and have them do the manual J heat load. Replace the oversized furnace with one that fits your needs.
The Flame Sensor Could Be Damaged
Another part of your furnace is a flame sensor, which shuts the furnace off if it detects an open flame. A corroded sensor won’t detect properly and may cause your system to shut down.
This is another job for a professional, but it does need to be checked if your furnace is short cycling.
How much is it to replace my furnace?
The average cost to replace a furnace is close to $4,000, but it can range from $1,800 to over $6,000. Unfortunately, the installation cost is usually between $2,500 and $6,000 for labor.
Can I fix the Furnace Myself?
Unless you’re HVAC-certified, it’s not recommended. If done wrong, you could shock yourself or release toxic gas into your home.
Change out your air filter and make sure to replace the batteries in the thermostat, but any actual problem should be handed off to a professional.