Power Out: What Size Generator to Power a Space Heater?

The cold winter months are not an ideal time to lose power, but it happens to all of us at one point or another. Typically it happens when an ice or snowstorm puts too much weight on a tree limb and it crashes onto the power lines below.

When this happens, our houses begin to get colder and colder.

If you’ve got an electric space heater for supplemental heat, you’re probably wondering if it can be powered with a generator and what size generator is needed.

The smallest generator that should be used to power a single electric space heater is 2,000 watts (2kW). This rated output will not be overburdened by the demand of the space heater and will prolong the life of the generator and also allow the user to power several LED lamps for lighting and charge devices.

That’s the short and sweet answer, but I’ve got some tables that might answer some of your other concerns below.

In this brief article, I’ll cover the electrical requirements of a typical space heater, what size generator is needed, and a safe and quiet alternative to the electrical space heater.

Let’s get started!

How Much Electricity Does a Space Heater Require?

Electrical space heaters are simple to calculate due to the fact that they put a resistive load on the generator instead of an inductive load. Put simply, there are no additional start-up watts to calculate like we would have to do with compressors like a fridge or window AC unit.

A 5,000 BTU AC unit uses about 450 watts when running, but requires a total of 1,800 watts just to start up, so we have to size our generator accordingly for that additional start up load. With electric space heaters, the watts used are what they are and do not change.

In this case, when I averaged out 3 space heaters from different makes and models and found that the average watts used on a high temperature setting were 1,300 and 720 for the low setting. The blower fan itself only uses about 25 of those watts in any of the given heaters.

Electric Heater Temperature SettingElectric Space Heater Watts Used

None of the models I tested had a “medium” setting, but if yours does then I would imagine it would average at about 1,000 watts.

electric space heater watts on high temp
The high watts hover around 1,290 and 1,320 on any of the given makes and models that were tested.

What Size Generator is Needed to Power a Space Heater?

Since we know that there are no additional start-up watts required for electric space heaters, picking a generator is pretty straight forward.

The smallest output generator that should be used to power a single electric space heater is 2,000-watts. This allows you to also run a few LED lamps, charge your devices, and not max out the generator and shorten its serviceable life.

While a smaller 1,000 or 1,500-watt generator may be able to handle the task, they certainly won’t do it for long since you’ll be maxing out their capacity. This shortens their lifespan by overheating the components inside.

It’s generally best practice to size up your generator by 20-25% to avoid doing this.

Electric space heater watts on low temp settings
The low setting watts hovered between 700 and 730 on the various makes and models that were tested.

Most generators are advertised at a certain output, but if you look in the manual you’ll see that the advertised watts are the max watts and that output should only be reached for 30 minutes or less before damage occurs to the generator.

So, for example, a 1,000 watt generator may have max watts of 1,000 but the actual running watts for long-term use may be 700. That is likely not going to be enough to start up your space heater (which usually starts on “high” before you switch it to a lower output setting).

Number of Space Heaters to Be PoweredMinimum Generator Size Needed
12,000 Watts (2kW)
23,500 Watts (3.5kW)
35,000 Watts (5kW)

A Safe and Quiet Alternative to Electrical Space Heaters

Running the space heater at night is probably going to be a big concern for you so that you don’t wake up freezing. Your generator, however, is going to be pretty noisy and may interrupt your sleep as well as your neighbors’.

To keep neighborhood relations calm, you might want to check out a Mr. Buddy propane space heater (Amazon). These are incredibly safe with the following features:

  • An automatic shutoff if carbon monoxide levels should happen to rise
  • An automatic shutoff if the unit starts to tip over

I’ve used two of these for years when camping, hunting, and during power outages and I’ve never had a problem with them. I always check the automatic tip-over shutoff with each use and it has never failed.

image of author showing a propane space heater and propane canisters as an alternative to electric.
I’ve got lots of canisters and 2 Mr. Buddy Heaters in my crawlspace for power outages. These have been worth every penny!

Regardless, I always believe in redundancies for safety so I believe it is best to also have several battery operated carbon monoxide detectors in the same room that you’ll be sleeping in or using your propane space heater.

At the time this article was written (summer 2022), the price gouging on Amazon for the 1 pound propane canisters is out of control and I highly recommend checking out your local Walmart as the prices listed online are 1/3 the price per canister.

Robert Van Nuck

Robert lives in central Michigan and enjoys running, woodworking, and fixing up small engines.

Recent Posts