Table of Contents
- Furnace Cycling – The Basics
- How Often Should My Furnace Cycle, Ideally?
- Furnace Cycling Depends on These 5 Factors
- Furnace Short Cycling
- Frequently Asked Questions (FAQ)
- How many times does a furnace cycle per hour?
- How Often should Furnace Cycle in Winter?
- How often should a furnace cycle in 0-degree weather?
- How often should a 2-stage furnace cycle?
- How often should a gas furnace cycle on and off an hour?
- How often should a propane furnace cycle on?
- How often should oil furnace cycle?
- How often should gas furnace cycle in winter?
- How often should an 80% efficiency furnace cycle?
- How often should 90% furnace cycle?
- How often should an older mobile home electric furnace cycle off and on?
- How long should a furnace cycle last?
A furnace at your home is just like a gentle waiter at a restaurant- it comes as you need and doesn’t overstay.
This on-and-off routine is technically called ‘Furnace Cycling.’ Proper cycling is essential for indoor comfort and the furnace itself.
But if you ask- “How often should a furnace cycle?” it can be anything between 3 times/hour to 8 times/hour.
But that’s not an answer that you’ll take, right? We need to be more specific.
Well, stick to the end of the post; we’ll try to enlighten you on the topic in depth.
Furnace Cycling – The Basics
Most gas furnaces work through the ‘forced warm-air distribution system’. Two of the key parts of the system are the burner and the blower motor. To define furnace cycling, you must understand these two parts’ roles.
While your thermostat detects a temperature drop, it lets the burner prepare hot air through the heat exchanger. Afterward, the blower fan sucks the air in and delivers it into your room through the duct.
This process would turn the burner first, wait a bit, and turn on the blower fan. Once the temperature reaches the preset point, the system will turn off. Once there is another drop in temp, the whole process will repeat.
And the entire process is called the ‘Heating Session’ of the furnace.
Heating Session(min)= Burner Runtime Fan Runtime
Furnace Cycle Frequency= 60/Heating Session(min)+ Temp Drop Time
How Often Should My Furnace Cycle, Ideally?
As I’ve told you, this question has no rule of thumb. At least 5 determiner factors might affect it for any individual.
And we’ll discuss them in-depth in the next segment.
But for now, we can give you an idea of the RANGE of furnace cycling regardless of the determiner factors.
Have a look at the chart below-
1 Heating Session(Ideal)
|Min 0||Min 0-1||Min 1-2||Min 3-4||Min 6-7||Min 7|
|Thermostat marks a temperature drop||The burner starts||The blower fan starts||The burner stops||The blower fan stops||The temperature raises|
Therefore, an ideal heating session runs for about 7 minutes. And such a session will take place once every 8-20 minutes until the temp drops again.
Verdict? The furnace cycling frequency will be 3-8 times/hour.
Furnace Cycling Depends on These 5 Factors
Factor 1: How Big/Small is The Home?
It’s an HVAC 101, the bigger space your furnace has to cover, the more frequent it will be with its cycling. This leads us to a common mistake that new homeowners often make. And that is- purchasing the wrong size furnace for the home.
When a furnace is meant to cover a small home, you’re not supposed to install it in a big one. If so, it will turn on and off more frequently. Needless to say, that’s not good for both of your furnace and home.
For a quick fact-check, here is a table showing the required furnace BTU/square feet of a home in different climate zone-
|Region 1||Region 2||Region 3||Region 4||Region 5|
|30-35 BTU/sq. ft.||35-40 BTU/sq. ft.||40-45 BTU/sq. ft.||45-50 BTU/sq. ft.||50-60 BTU/sq. ft.|
Keeping the formula in mind, keeping your house well-insulated is essential, which brings us to our next point.
Factor 2: How Insulated is the space?
Properly insulated spaces are less likely to lose temperature than insulated ones. If the temp difference is significant between the inside and outside of the home, this loss will be even faster in a poorly insulated home.
As a result, the furnace cycling will be faster, which will not be wallet-friendly for you.
Causes of Poor Insulation
So, what causes poor insulation in a house?
- Old age(15 years or more) house.
- Poorly insulated walls, doors, and windows.
- An unnecessarily large number of windows (more than 2/room).
- Old-school windows and door designs.
- Multiple stories inside the house.
Factor 3: One-Stage or Two-Stage Furnace?
Based on how many ‘speed stages’ there are, furnaces can be split into two categories-
- Single-stage furnace.
- Double-stage furnace.
Single Stage Furnace
In a single-stage furnace, there is only one furnacing stage with a fixed motor speed. What I mean is, it can either turn off or turn on at a fixed speed. There’s nothing in between.
These furnaces are old school, come with a cheap price but can cost you some serious amounts in the energy bill.
Double Stage Furnace
On the other hand, two-stage furnaces have two motor speed options on the ‘On stage’. It means it can do these three tasks-
- It goes full blast(100%) to heat up cold air.
- It runs at a slower speed(50%) to maintain the temperature and warm the furnace up.
- It stays at an ‘off’ mode(0%) with no heating.
In case it has an ECM motor, it can also sport more speed variations and cut a good amount in your monthly energy bill.
Factor 4: What’s The Temp Outside?
A cold atmosphere in the winter will affect your indoor temperature faster than other seasons, no matter what you do. But with proper insulation, you might earn a little more time before your furnace kicks in to heat your home.
So, when it’s freezing outside, don’t worry if your furnace cycles too often. Instead, keep your eye on these two facts-
- Insulate the home in every possible way.
- Make sure that the furnace warms the home to the desired temperature (in the thermostat).
On the other hand, in the other seasons where it’s not-so-cold out there, you might find the furnace cycle less often.
Factor 5: The Furnace Efficiency
Every new gas furnace in the USA is assigned an AFUE (Annual Fuel Utilization Efficiency) rating before they’re taken public. Although the AFUE rating addresses the percentage of fuel a furnace might use, it also has a role in determining its cycling frequency.
The question is- Do high-frequency furnaces run more often?
Yeah, they do. But that’s for a good cause and it’ll reach no harm to your comfort and the furnace itself. By running more often, they don’t let the temperature drop massively and prevent any noticeable difference in comfort as well.
Furnace Short Cycling
A term very related to furnace cycling is the ‘Short cycling’ of the furnace. It’s a situation where the furnace cycle ‘shortens’ up and be more frequent than what it should be.
Two symptoms can tell you that short cycling is going on with your furnace-
- It turns off before reaching the desired temperature.
- It’s turning on and off too frequently than usual.
A Common Myth about Short Cycling Furnaces
A lot of us might suspect short cycling in the furnace just from the fact that it’s turning on and off more frequently. But that might not be a sign of short cycling at all!
Well, depending on the room/home size and outdoor temperature, the room temperature might change too fast than usual. As a consequence, the furnace will show up to sort it out. And that’s nothing to worry about.
You will suspect short cycling only if the furnace stays for a shorter time span than what it should do. If it’s supposed to stay on for 3-5 minutes in every ‘heating cycle’ and it stays only from a few seconds to a minute, that’s a serious problem that you should worry about.
Frequently Asked Questions (FAQ)
How many times does a furnace cycle per hour?
In usual cases, an ideal furnace should cycle 3 to 8 times in an hour. Based on external factors and the furnace size, this might vary.
How Often should Furnace Cycle in Winter?
Winter is the time when a furnace has to work the most. So, the average single-stage furnace should cycle 6-8 times in an hour. The cooler the temperature is, the more this cycling frequency will be.
How often should a furnace cycle in 0-degree weather?
It’s 6-8 times/hour usually. Zero degrees is quite a low temperature in winter. During then, your furnace has to work hard with a lot of stress on it.
How often should a 2-stage furnace cycle?
Answer: Two-stage furnaces work longer than single-stage ones. Thus, it should cycle 1-3 times in an hour and the heating session will be 8-12 minutes each time.
How often should a gas furnace cycle on and off an hour?
A gas furnace should cycle on and off 3-8 times an hour, ideally. That’s usually the most common case with furnaces.
How often should a propane furnace cycle on?
Propane furnaces also need to cycle 3-8 times in an hour. Most of the gas furnaces run on propane and are called ‘propane furnaces’ as well.
How often should oil furnace cycle?
Oil furnaces are less efficient than gas furnaces. So they’ll run more often. The furnace cycle will be about 6-10 times in an hour in any mild condition.
How often should gas furnace cycle in winter?
Although gas furnaces are efficient, they have to work hard in winter. If the winter temperature is above zero, it’ll be 3-5 times in an hour. It’ll be even more frequent if it’s zero degrees or less.
How often should an 80% efficiency furnace cycle?
80% efficient gas furnaces will run 3-4 times in an hour, given that you’ve got a sealed house with not-so-cold outdoor temperature.
How often should 90% furnace cycle?
90% efficient furnaces are less likely to waste energy. This works for 2-3 times in an hour. And the overall temperature drop will be relatively less noticeable.
How often should an older mobile home electric furnace cycle off and on?
Mobile home lets the furnace deal with a very small air volume. Given that it’s adequately insulated, the furnace might work 3-5 times in an hour.
How long should a furnace cycle last?
Answer: A furnace cycle lasts for 6-10 minutes in ideal situations. Based on many external parameters, it might vary a lot.
HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.