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What Size Generator to Run Furnace

What Size Generator to Run Furnace

Choosing the right size generator to run your furnace is essential. You want to make sure that it can handle the load you are putting on it and be cost-effective for your situation.

In this blog post, we will explore what factors go into choosing a generator and what size generator to run furnace that works best for you.

How Many Watts Does a Furnace Use?


Choosing the right size generator for you comes down to knowing how much wattage you’re looking to power. When choosing the right generator for you, wattage is a crucial factor to look at.

The average home furnace uses between 3500-5000 watts of power which translates into about 12 amps on a 120-volt circuit or 20 amps on 240 volts (most homes are wired with two circuits).

The best way to find out how many watts your furnace uses is to read the back of your furnace.

It should list a model number and either an input or output voltage, which you can then use to calculate watts using the formula:

Watts = Volts x Amps

So if our furnace runs on 240 volts and has a 20 amp draw, we get Watts=240voltsx20amps=4800watts.

In this case, you would need a generator with enough power to run your furnace on 240 volts.

Using our example of 12 amps per 120-volt circuit, you will need about 167 Amps at 120V or 250-300Amps at 240V (which most generators are rated in).

So a generator that is rated at 300 Amps or higher would be your best bet.

Read: Propane generators: merits and demerits

What Size Generator to Run Furnace

man with furnace
man using furnace

Generators that can run a furnace include:

1. Gasoline Generators

These are the smallest and cheapest to buy and have much less power than other generators.

It is vital to make sure you get one with enough wattage for your furnace’s needs and any other items it will be powering at the same time.

2. Natural Gas Generators

They are probably the best option for running a furnace.

They do not need to be refueled as often and typically produce more wattage than diesel or gasoline models, but they also come with an increased price tag.

A natural gas generator can range in power from about 5000 watts to 30,000 watts which should cover all of your needs.

Read Also: Carbon monoxide generator exhaust

3. Diesel Generators

They are the most popular generators for powering a furnace. They are widely available and offer the same wattage as natural gas generators but have a cheaper initial cost.

A diesel generator can range from about 7000 watts up to 45,000 watts, so it should be able to handle your needs as well as any other appliances you need running at the same time.

Alternative Energy Generators such as Solar or Wind-powered Generators

They can be a very cost-effective way to run a furnace. However, most of these systems do not deliver the wattage you need for most home appliances, including a furnace.

Read: Types of generators for home use

How to Choose the Right Generator Size to Run a Furnace?

Now that you know how to calculate your wattage needs, it is time to choose the right generator for you. Here are some things to consider when looking at different generators:

  • Price– Generators can range in price from a few hundred dollars to a couple thousand with a vast array of features and benefits.

If you’re looking at powering equipment that runs 24/7, it might be wise to purchase one of the most expensive generators. Still, if you’re powering an occasional furnace during power outages, then you may want to go with a much cheaper model.

  • Size– If you are trying to power too much load for a smaller generator, it will overload, which could damage both itself and other equipment. Then you will need to upgrade your generator or try powering through multiple generators, so make sure you know how many watts your equipment is drawing.
  • Noise– If you are powering a furnace that runs 24/hrs, noise may not be too much of an issue. However, if it’s going to be powering something like a sump pump or other appliances in the house, then having a generator with lower decibels might make more sense for your situation.
  • Fuel type– The kind of fuel you will be using can significantly influence your purchase decision. Gasoline generators are the most common, but propane and diesel-powered units have a few advantages over gas, such as their ability to run longer during colder weather without having to turn on and off.
  • Emissions– The emissions that a generator produces will significantly influence where you decide to power it. If your property is close to sensitive areas, then gas generators might not be the best choice for you as they produce more air pollution than other types of fuel do.

Propane-powered generators for home use

Frequently Asked Questions on Furnace Generator Sizes

Can I Run My Furnace On a Generator?

If you are planning on using a generator during an emergency, then the answer is yes! You can easily use it to power your furnace during any significant power outage. Many people choose to use them during storms or other natural disasters as they tend to be more reliable than grid-connected power plants, which can fail due to weather-related issues.

What Size Generator Do I Need to Run My Furnace?

Choosing the right size generator will depend on your wattage needs. If you are powering a furnace that runs on 240 volts, you will need at least 250-300Amps of power to keep it running during an emergency or if you have too many items plugged into one circuit. If you are only powering the furnace and maybe a few other appliances, then a smaller generator rated at about 100A will do.

How Many Generators to Run My Furnace and Home During an Emergency?

The number of generators you need to power your home will depend on what types of fuel you use as well as how much energy your appliances consume. Keep in mind that even if your home is running off of generators, it will still need the regular maintenance and service of a grid-connected power system.

Running your furnace during an emergency is simpler than you might think when you have the right equipment.

The size of the generator you will need to run your furnace will depend on how many appliances are plugged into each circuit and what kind of fuel they use.

Make sure you know what wattage your appliances produce so that you can pick out the right size generator, and look at our website for more information on the generators.

If you have any questions or something that we didn’t cover, please leave us a comment below.

Read: What is the best dual fuel portable inverter generator

References and Citations:

New York State; Department of Health: Generators and Heating Safety-

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