Best Generator Sizes to Run a Furnace

Running a furnace in your home lets you keep the house warm, but you need a way to run it. If you own a generator, you need to see if your furnace works with it. Unfortunately, the situation leaves people wondering what size generator they need to run a furnace.

If your furnace can run on a generator, you must understand the sizes and watts available. Doing so will help you know if your generator works for your furnace or if you need to purchase a new generator.

Overview of the Article:

  • Which generator watt sizes can run a furnace
  • Why you would want a larger or smaller generator
  • Frequently asked questions about running furnaces with generators

As winter approaches, it’s crucial that we keep hot air flowing through our homes. There’s no better way to achieve this than with a furnace. However, furnaces need power to run at their best in winter and all year long, and generators play a big role in it.

As you look into the details and review the FAQs, you’ll understand generators and how to get your furnace running off of one.

Engineer Installing A Furnace Water Heater
Best Generator Sizes To Run A Furnace 3

What Size Generator Do I Need to Run My Furnace?

The generator size needed for a furnace depends on a few factors. 

  • The size of the furnace.
  • How much horsepower a generator can handle.
  • Any additional equipment you plan to attach.

Furnaces have various sizes and require different amounts of power. For example, a furnace that requires two horsepower will need more watts than a furnace with one horsepower.

You also must think about additional appliances you plan to connect. For example, while most people connect generators to multiple devices, you may not need to worry about a more significant generator for just a furnace.

On top of this, you must strive to run your generator at full load. Doing so means getting your generator to max capacity when possible so you don’t damage it.

You must consider how much power you plan to use before getting a generator. As you do, you must focus on keeping your generator at full load.

How Many Watts Does My Furnace Need?

Some people assume they just need a generator with enough watts to run a furnace. However, you must consider the watts needed to start the furnace since that varies from the required amount.

For example, most appliances require double the watts to turn them on and keep them running. With this in mind, if your furnace needs 2,000 watts to run, then you need a generator that can handle 4,000 watts.

With this in mind, we want to talk about different generator watts, if they can run furnaces, and if you can use additional appliances with them. Doing so will help you gauge which generator works best for your situation.

See also  What Size Generator To Run Refrigerator And Freezer? (+ Best Ones For You)

For example, you need to go with a larger generator if you want to connect multiple devices to it. On the other hand, a smaller size works well if you only want to worry about heating and a few other appliances. You can also swap devices as needed.

As we go through the different sizes, you can see which options help you in your situation or home size.

Will a 7,500-Watt Generator Run a Furnace?

As you check furnace blowers, you’ll notice one requires 0.25 to 0.5 horsepower to run. So every 0.25 horsepower your furnace uses, you need to have about 1,000 watts. While it seems like a furnace can heat a home at a lower output, that isn’t always the case.

When it comes to a 7,500-watt generator, you can efficiently run a furnace off it with enough power to heat your home. It also works great if you plan to add multiple appliances such as your lighting, the fridge, or any other essentials.

You also have space to add a few other appliances you don’t need. For example, the 7,500-watt generator works excellently if you want a flexible furnace or to heat a larger house.

Furnace Home And Water Heating
Best Generator Sizes To Run A Furnace 4

Will a 6,500-Watt Generator Run a Furnace?

Going off the previous point, you can use a 6,500-watt generator to run a large furnace. You can attach most furnaces to this size and still have some power left over for other appliances. 

For example, you can add a fridge, your lights, and maybe another necessary appliance. You could potentially add other devices to it, but you need to realize it doesn’t have as much flexibility as a 7,500-watt option.

However, if you don’t have enough appliances to add to your generator to warrant a 7,500-watt option, this one works great. You can also go with it if you want to focus on necessary or important appliances rather than ones you want to use during a power outage.

Despite that point, you most likely will have a bit of room for one or two additional appliances.

Will a 5,000-Watt Generator Run a Furnace?

You can use a 3,000 or 5,000-watt furnace to run most houses when it comes to generators. However, since this one sits at the higher end, it can run a furnace, a fridge, lights, and similar appliances.

The 5,000-watt option gives you additional power for other appliances you want to attach. However, if you own an average-sized home, you may not have as many options for your generator.

Some people don’t mind swapping appliances on their generators as needed, so a 5,000-watt option could work for some larger homes. However, if you want to avoid switching appliances, go with a 5,000-watt option to cover your essentials in an average home.

Will a 4,000-Watt Generator Run a Furnace?

A 4,000-watt furnace has a similar approach to the 5,000-watt option, but you’ll need to give up an appliance. Since multiple essential devices require about 1,000 watts to turn on, you may not have enough power to run another machine.

However, a furnace can efficiently run off a 4,000-watt generator while providing room for a few other appliances. So if you own an average home or a smaller one, the 4,000 option might work for your entire home.

See also  Wen Generator Reviews (Powerful Vs. Quiet)

You also can swap appliances when you need to use different ones. However, you won’t find as much flexibility as the larger options, so stick with the essentials.

Will a 3,500-Watt Generator Run a Furnace?

While 500 watts may not seem like a significant difference, it can prevent an entire appliance from working with your generator. You don’t want to go over the maximum watts since it can damage your generator, so you must know how many watts you plan to use.

A 3,500-watt generator can power an average home with just the necessities or a smaller one with a few other appliances. With this in mind, you could run a furnace with a fridge, but you may not have enough power for more appliances.

The 3,500-watt generators also work well as portable options. You can bring them with you on a trip and use them to power a couple of appliances. However, you need to push it to its limit if you want it to power an average house or use it for a few other items with a smaller home.

Will a 2,000-Watt Generator Run a Furnace?

While a 2,000-watt generator can run a 0.25 or 0.5-horsepower generator, it won’t work for most situations. For example, you can power your furnace and heat your home, but you can’t add other appliances.

You may use the furnace, but you might not have enough watts to add the lights. You may also struggle to use your fridge and the heater simultaneously, so you could lose food if your fridge gets too warm.

In short, 2,000-watt generators work for light use, so don’t rely on them for powering multiple appliances. However, if you only need to worry about one machine during an outage, a 2,000-watt generator can work well.

Because of this, a 2,000-watt generator won’t work for most people, but you can use it if you want to. They work better as portable power sources when people want to use appliances as they camp.


Now that you understand which generator sizes can run furnaces, you must check out the frequently asked questions (FAQs). Doing so will help you address concerns and problems with generators or furnaces.

Will A generator damage my furnace?

If you don’t correctly use your generator, you could damage your furnace. In addition, when you overload the generator, you could face the following side effects:

  • The process permanently damages the generator and any appliances attached to it.
  • The generator can overheat and pose a fire hazard.
  • If fuel spills out, the generator could explode and damage more property.

If you follow the instructions and properly use your generator, you won’t need to worry about damage. Make sure never to plug in more appliances than the generator can handle. Each generator states its max load.

Instead of pushing your generator to the limit and facing potentially deadly consequences, you need to buy a new one as necessary. Even if your generator doesn’t catch on fire, you can still damage your furnace.

Can I plug my gas furnace into a generator?

You can, but it depends on the furnace type. If the furnace requires an electric motor, it may need to be plugged into a power source to work. However, other furnaces only run on gas, so you can’t plug them into your generator.

See also  Why You Need A Backup Generator (Be Prepared)

If you plan to use your generator to power your gas furnace, you need to double-check the instructions. First, look at the instructions for both the gas furnace and the generator. You can see if they mention any warnings concerning their use with furnaces.

If you can’t find any information about safely using your gas furnace with a generator, don’t use them together. Doing so could pose fire hazards, so you don’t want to risk anything. If you need to know for sure, call the manufacturers for more information.

How do you hook up a furnace to a generator?

If you want to hook your furnace to the generator safely, you need to follow these steps.

  • Review the manual for any specific instructions or quirks concerning the generator.
  • Always use the generator outdoors to avoid any gas leaks or damage in your house.
  • Turn all the appliances off and plug them into the generator.
  • Turn the generator on.
  • Turn each appliance on one at a time to avoid overloading the generator.
  • Check the generator every once in a while to ensure it doesn’t overheat or face problems.

These steps keep you safe and avoid damage to your generator and furnace. Make sure you take it slowly to minimize issues and mistakes.

What size generator do I need to run my furnace and refrigerator?

Although it depends on the power required to run a furnace and refrigerator, a 3,000-watt generator should work in most situations. You could also use a 2,000-watt one if you need to heat less space or have a mini-fridge.

However, if you think a 3,000-watt option won’t work for your fridge and furnace, you could try a 4,000-watt one or a larger generator. Of course, you need to think about the size of your house as you pick one, so look at these numbers as rough estimates to get you started.

What size furnace do I need for my house?

The furnace size you need depends on your house size. For example, a 1,500-square-foot house will require a smaller furnace than a 3,000-square-foot house. If you know the size, you can use a furnace size calculator to help you figure out what you need to buy.

Check how much horsepower you need for the required appliances as a general guide. You can figure out how many watts you need to power your home as you remember these points.

What size generator do I need for a 1,500-square-foot house?

You can go with a smaller generator to run a 1,500-square-foot house. While it may vary depending on what you plan to plug into your generator, you can use a 3,500-watt generator for the basics.

Double-check how much power your furnace, fridge, lights, and other essentials required to run. While a 3,500-watt option might work, you may need a larger one depending on what you plan to plug into it.