How Often Should a Furnace Cycle?

If you’re having furnace problems, you may be wondering how often a furnace is supposed to cycle.

On the average, your furnace should cycle four times per hour. But your furnace may cycle more or less often than this based on a variety of factors, including the outdoor temperature, the furnace’s efficiency, and the size of the HVAC system.

If you’ve still got questions about your furnace cycle, you’re in the right place. Keep reading to learn everything you need to know about the topic.

How often is a furnace supposed to cycle in winter?

When it’s really cold outside, this can cause your furnace to cycle more often. That’s because it might need to do so in order to keep up with your increased heating requirements.

But your HVAC system shouldn’t turn on and off every few minutes—even in the dead of winter. If it does, that’s likely a sign that some aspect of your heating system needs adjustment.

There are a variety of factors that can influence how often your heater cycles in winter. We cover each of these below.

Your home’s insulation

Insulation is what allows your home to retain warmth. If your insulation isn’t very good, then your furnace has to work harder to keep it warm.

A furnace in a home with average insulation may cycle two to three times per hour to maintain temperatures. If yours does more than this, then that could be because your insulation isn’t very good.

There are a few signs to look at to see if your home is well-insulated or not.

• Looking at your wall and floor temperatures is a good first step. You can place your hand on interior walls and floors. If they feel warm and dry to the touch, that’s a good sign.
• Freezing pipes can be another sign of poor insulation. If your pipes freeze (or even bust) with some regularity, there’s a good chance that your insulation isn’t right.
• Cold drafts running through your home can be another sign that you lack proper insulation, as can water leaks in your attic and around your windows.
• The best sign of proper insulation is consistent temperatures. If you have these throughout your home, it’s likely well-insulated throughout.

Correct furnace size

You also need to make sure that you have the correct furnace size if you want proper cycling. This will vary based on your home’s square footage.

On average, you need about 30-60 BTUs per square foot. But the exact number depends on your climate. Warmer climates might need just 30-35 BTUs. But colder ones could need 50-60.

There are two main signs that your furnace may be oversized:

• It runs for a short amount of time before shutting off
• Your home has some rooms that are uncomfortably hot and others that are uncomfortably cold

One or two-stage HVAC system

Whether you have a one or two-stage HVAC system can also impact cycling timing.

A one-stage HVAC system typically operates with something like an on-off switch. They’re either working at full power or not at all. This type of HVAC system is more common with older models.

Two-stage HVAC systems can heat and cool and both fast and slow speeds. They tend to have longer cycles and produce smaller temperature swings. Most two-stage furnaces cycle one to three times per hour.

Furnace efficiency

The efficiency of your furnace is another sign to look at while thinking about cycles.

High-efficiency furnaces tend to run more often. They do that to save you money on your energy bills. These typically run about 80% of the day or longer. They work about two to three times per hour.

The average run time of a furnace cycle

Given all of that information, the average furnace cycle run time is between 10 and 15 minutes.

That doesn’t necessarily mean something is wrong with your furnace if its cycles are shorter or longer than this. But if you keep seeing long or short cycles during mild conditions, you may want to do some investigating.

Generally, the longer your cycles, the better for the lifespan of your HVAC system. That’s because starting and stopping is what causes wear and tear to your system.

When a furnace only turns on for a few minutes at a time and doesn’t warm your home, it’s a sign of short cycling. If this keeps happening to you, it’s time to have it inspected by an HVAC professional.

Potential problems that can cause cycle timing

If you’re having furnace cycling issues, it could be a sign that there’s a problem with your system. There are a few different things you can look at to fix this.

Incorrect unit size

Incorrect HVAC size can also cause cycling problems. If you’ve recently had a furnace installed and just noticed this happening, it could be the wrong size for your space.

Furnaces that are too large may heat your home faster than normal. And furnaces that are too small may heat your home slower than normal.

Both of these are bad for a few reasons. First, it can mess with your cycle times. If your unit is the wrong size, the cycles may take longer or shorter than they should.

Additionally, this can put extra strain on your system. That may cause it to wear out faster than it should.

Dirty filter

A dirty filter can also cause furnace cycling issues. When filters have too much dirt in them, the system can’t get enough air. This can cause overheating, which leads to the system shutting down too early.

Poor duct design

Your HVAC system needs well-designed ductwork to receive the proper amount of airflow. If your ducts aren’t designed correctly, it could take too long for the heated air to reach your desired temperature. This can cause overheating and premature shutdown.

Faulty thermostat

Your thermostat may also cause cycling issues. For example, yours might sense the wrong temperature. And that could cause it to send a signal to your furnace either too soon or too late. The accumulation of dirt on your thermostat sensors can cause your thermostat not to reach the set temperature.

Your thermostat might also be running out of battery. This can cause it to act erratically and may mess with your cycle timing.

Heat exchanger issues

Gas furnaces have heat exchangers that take heat from flames and transfer it into the air that goes throughout your home. These can sometimes crack or malfunction. When that happens, it can increase the amount of time it takes to heat your home.

There are three phases in the standard heating cycle

As you think about furnace cycles, it’s worth knowing that these happen in phases. Understanding each of these phases can be helpful as you work to improve the efficiency of your system.

So with that in mind, here are the three phases of the standard heating cycle.

1. Draft induction

The first phase is called draft induction. This is when the thermostat detects that there’s a need for heat in your home. When that happens, it sends a signal to your furnace’s control board.

Next, the control board turns on the draft inducer fan. This pulls air through the combustion chamber and supplies oxygen to the burners. Once the fan reaches its full speed, the control board begins the ignition phase.

2. Ignition

The ignition phase begins with the furnace ignitor. Older systems use a pilot light for this.

But newer systems have an electric ignitor. This turns off and on when you ask it to rather than remaining on constantly.

When the ignitor is ready to go, the gas valve opens up. Then, gas flows over the ignitor and lights the burners.

There’s a safety device near the burners. This device (limit switch) is designed to assess the temperature of the combustion chamber.

Once that temperature gets warm enough, a signal gets sent to your furnace’s blower motor.

3. Air distribution

Now the blower motor is on, and the warm air is ready to be distributed throughout your home. This starts in your home’s supply ducts. The air moves through these ducts to get to different rooms throughout your house.

As the cycle keeps going, the air is then drawn out of your rooms through return vents. This air goes back into the furnace to get warmed up again.

This cycle keeps going until your home reaches the desired temperature. At that point, the system shuts down and waits until the next heating cycle is needed.