How Many Watts Does A Gas Furnace Use? (Blower Wattage)

Gas furnaces can use quite a lot of electricity. This may come as a surprise. Gas furnaces use natural gas or propane to produce heat, right? Why would we talk about how many watts does a gas furnace use if it doesn’t run on electricity?


  • For heat production, gas furnaces do use natural gas or propane. The main running cost associated with gas furnaces is the price of this fuel. Electric furnaces, for example, use electricity to produce heat and can use anywhere from 10,000 watts to over 45,000 watts of electric power. A standard 20,000 BTU natural gas furnace will, on average, cost $208.80 per month to run.
  • For powering the air forced furnace blower, however, gas furnace needs electricity (up to 735.5W, in fact). An average 1/2 HP furnace fan motor runs on maximum wattage of 368W and can cost more than $10 per month to run.
how much watts does a furnace blower fan motor use
Blower fan motor is the main consumer of electricity in gas furnaces. A standard 1/2 HP draws 367.8W when operating at 100% output.

Example: If you have a power outage, the gas furnace will stop running (we will look into generators for gas furnaces further on). Why? Well, because it needs electricity for two vital functions, namely:

  1. Gas furnaces use electricity for ignition. Modern electronic igniters use a minimal amount of electricity for the ignition spark. Older glow plug ignitors will use more electricity because they need to stay glowing hot when a gas furnace is running.
  2. Gas furnaces use electricity for powering a furnace blower motor (most run on 110-120 volt circuits). This is the main electric power consumption component of every gas furnace. This motor powers the furnace fan; and it can draw significant wattage.

Gas furnace ignition wattage is insignificant in most cases. So, when we are asking how many watts does a gas furnace use, we are really asking this question:

“How many watts does a furnace blower use?”

We will look into exactly how many watts does a furnace fan use. Based on this, we will also look into:

  1. How much electricity will a gas furnace spend per month. Here we only need to look at blower fan wattage.
  2. What size generator do you need for a gas furnace (in event of a power outage, for example). Here we need to look both at blower fan running wattage as well as gas furnace ignitor wattage.
gas furnace ignitor wattage
When figuring out the generator size for a gas furnace, we need to add the start-up wattage of the electronic ignitor (about 600W).

How Many Watts Does A Furnace Blower Use?

Gas furnace blower can use anywhere from 50 watts to 735.5 watts of electricity. You can figure out the maximum wattage of a furnace blower yourself by checking how many watts does an air forced gas furnace blower fan use.

Instantly, however, you will encounter this problem:

The furnace blower motor’s power draw is not expressed in watts. Rather, it is expressed in horsepower (HP). In gas furnaces, we use 1/6 HP, 1/3 HP, 1/2 HP, 3/4 HP and even 1 HP motors. When figuring out furnace fan wattage, we need to convert HP to watts (1 HP = 735.5 Watts).

Here are some examples:

  • 322P289 Coleman furnace blower motor has a maximum output of 1/6 horsepower. That means the Coleman furnace fan will run on 122.6 watts when operating at 100% output.
  • 60L21 Lennox furnace blower motor has a maximum output of 1/3 horsepower. That means the Lennox furnace fan will run on 245.2 watts when operating at 100% output.
  • 5KCP39HGS599S Trane American Standard GE Genteq (multiple brands) furnace blower motor has a maximum output of 1/3 horsepower. That means the Trane, American Standard, GE, and Genteq furnace fans will run on 245.2 watts when operating at 100% output.
  • B13400-20 Goodman furnace blower motor has a maximum output of 1/2 horsepower. That means the Goodman furnace fan will run on 367.8 watts when operating at 100% output.
  • X-13 GE – Genteq Evergreen furnace blower motor has a maximum output of 1 horsepower. That means this Gentreq furnace fan will run on 735.5 watts when operating at 100% output.

1 HP motor is the biggest furnace fan motor. That means that all gas furnaces run on 1 HP or 735.5 watts or less.

Obviously, the gas furnace blower fan doesn’t run on 100% all the time. In fact, variable-speed furnace motors can reduce the average wattage of a blower fan motor by a factor of 5. Example: 1/2 HP motor runs at a maximum wattage of 367.8W. If this is a variable speed fan motor, it can run on average on less than 100W in practice.

1/2 HP motor is the most commonly used motor size in gas furnaces. We can use this information to both calculate how much electricity will a gas furnace spend per month, as well as adequately size a generator needed to power a gas furnace in the event of a power outage:

How Much Electricity Will A Gas Furnace Spend Per Month?

When you figure out the wattage of your gas furnace fan motor, you can calculate how many kWh will such a gas furnace motor cost to run per month.

Let’s say that we have a standard 1/2 HP motor (367.8 maximum wattage), run a furnace for 8 hours per day, and let’s presume that the price of electricity is the US national average of $0.1319/kWh.

If such a motor would run at 100% output all the time, here is how many kWh will it spend per month and how much it will cost:

Electricity Expenditure (1/2 HP Motor) = 367.8W × 8 Hours × 30 Days / 1000 = 88.3 kWh Per Month

In short, a 1/2 HP motor will spend a maximum of 88.3 kWh of electricity per month. If we multiply the expended kWh by the price of kWh we get the monthly electricity bill for powering a gas furnace:

Electricity Cost Per Month (1/2 HP Motor) = 88.3 kWh × $0.1319/kWh = $11.65 Per Month

Now, you are most likely not going to pay $11.65 per month for electricity that powers the gas furnace fan. That’s because most furnaces use variable-speed fans that can reduce the average output need to about 20% from 100%. That’s a factor. So, you will likely pay closer to $2.33 per month.

One of the biggest concerns with wattage required to run a gas furnace is in an event of a power outage. In that case, we will need a generator to power a gas furnace. Is a 500W generator enough to power a gas furnace? Let’s tackle this question as well:

What Size Generator Do You Need For A Gas Furnace?

When lights go out, we can always use a generator to produce electricity. You will find tons of questions about what size generator you need for a gas furnace. Is a 500W generator enough, or do you need a 1000W or even a 2000W generator for running a furnace?

Let’s use the exact specs to adequately size a gas furnace generator. Namely, you have to take into account two power draws from the gas furnace:

  1. Running a blower fan. This is a continuous draw that a generator has to supply. As we have seen in the case above, most gas furnaces will require a maximum wattage of 367.8W (this is a 1/2 HP motor).
  2. Ignitor wattage. This is an acute draw (a spark to start gas combustion). Gas furnace ignitors require a start-up wattage of about 600W or less. This won’t affect your energy bill but it will certainly impact the size of the generator you need.

If we want a generator to run a gas furnace, we will need to sum up all these wattages. For most furnaces, we will need a generator that has:

  1. 500W running wattage. Most furnace fan motors draw 1/2 HP of power; that’s 367.8W. It’s safer to get a little bigger than needed generator.
  2. 1000W start-up wattage. Start wattage should be the same as the sum of fan wattage (367.8W) and gas ignitor (600W) or higher. In most cases, this means you will need a generator with a 1000W start-up wattage.

The perfect example would be Honda EU1000I 1000W generator since Honda generators are considered top-notch. Here is this generator:

generator for running a gas furnace 1000 watts
You can get the Honda 1000W generator here.

Alternatively, you can also go with a bigger generator. A good option (that doesn’t cost $1000 like Honda 1000W generator) is this WEN 56203i 2000W generator:

good generator size for a gas furnace
You can get the WEN 2000W generator here.

You can use any other whole-house generator you may already have at home.

All in all, gas furnaces do use electricity. In most cases, you will need a 1000W generator to power the gas furnace during an outage. The electricity running costs of powering gas furnaces are usually quite low (less than $10 per month during the winter season in most cases).

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