how often should furnace cycle

How Often Should A Furnace Cycle?

A furnace at your home is just like a gentle waiter at restaurant- it comes as you need, and don’t overstay. 

This on-and-off routine is technically called ‘Furnace Cycling’. Proper cycling is super important for both of your indoor comfort and the furnace itself. 

But if you ask- “How often should a furnace cycle?”, we’re sorry to say that we don’t have a one-word answer to the question. It can be anything between 3 times/hour to 8 times/hour. 

But that’s not an answer that you’ll take, right? We definitely 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 Basic Knowhow

Most of the gas furnaces work through a process called the ‘forced warm-air distribution system’. Two of the key parts of the system are the burner and the blower motor. To define what a furnace cycling is, you’ve to understand the roles that these two parts play.

While your thermostat detects a temperature drop, it lets the burner to 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 whole 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 will be another drop in temp, the whole process will repeat over again. 

And the entire process is called ‘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 we’ve told, there’s no rule of thumb regarding this question. There are at least 5 determiner factors that 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 that 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 of furnace for the home. 

When a furnace is meant to be covering 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- 

climate zone map for furnace

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, it’s essential to keep your house well insulated. Which brings us to our next point.

Factor 2: How Insulated The Space Is?

Properly insulated spaces are less likely to lose temperature than the 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 and that’ll be not wallet-friendly for you at all. 

Causes of Poor Insulation

So, what causes poor insulation in a house? Here you go- 

  1. Old age(15 years or more) house. 
  2. Poorly insulated walls, doors, and windows.
  3. Unnecessarily large number of windows(more than 2/room).
  4. Old-school windows and door designs. 
  5. 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- 

  1. Single-stage furnace.
  2. Double stage furnace.

Single Stage Furnace

In a single-stage furnace, there is only one furnacing stage with fixed motor speed. What I mean is, it can either turn off or turn on with a fixed speed. There’s nothing in between. 

These furnaces are old school, comes 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- 

  1. It goes full blast(100%) to heat up cold air. 
  2. It runs at a slower speed(50%) to maintain the temperature and warm the furnace up. 
  3. 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 whatever you do. But with proper insulation, you might earn a few 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- 

  1. Insulate the home in every possible way. 
  2. Make sure that the furnace warms the home to the desired temperature(in 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 is the USA is assigned with an AFUE(Annual Fuel Utilization Efficiency) rating before they’re taken public. Although the AFUE rating addresses the percentage of fuel that a furnace might use, it also has a role to play to determine it’s 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- 

  1. It’s turning off before reaching the desired temperature. 
  2. It’s turning on and off too frequently than usual. 

A Common Myth about Short Cycling Furnace

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! 

Why? 

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 shorter timespan 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 some serious problem that you should worry about.  

Frequently Asked Questions(FAQ)

How many times does a furnace cycle per hour?

Answer: 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?

Answer: Winter is the time while 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 furnace cycle in 0-degree weather?

Answer: It’s 6-8 times/hour usually. The zero degree 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?

Answer: 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?

Answer: Propane furnaces also need to cycle 3-8 times in an hour. In fact, most of the gas furnaces run on propane and called ‘propane furnaces’ as well. 

How often should oil furnace cycle?

Answer: 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?

Answer: Although gas furnaces are efficient, they have to work hard in winter. If the winter temperature is above zero, then it’ll be 3-5 times in an hour. If it’s zero degrees or less, it’ll be even more frequent. 

How often should an 80% efficiency furnace cycle?

Answer: 80% efficient gas furnaces will run for 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?

Answer: 90% efficient furnaces are less likely to waste energy. This is works for 2-3 times in an hour. And the overall temperature drop will be quite less noticeable. 

How often should an older mobile home electric furnace cycle off and on?

Answer: Mobile home lets the furnace deal with a very small air volume. Given that it’s insulated properly, the furnace might work 3-5 times in an hour. 

How often should furnace cycle last?

Answer: A furnace cycle lasts for 6-10 minutes in ideal situations. Based on many external parametres, it might vary a lot.

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