Can I use an Extension Cord with a Space Heater?

Here’s everything you need to know about whether you can use an extension cord with your space heater.

You should treat space heaters with special caution when it comes to installing them in your house. If you need an extension cord, for example, you have to spend additional attention to some safety aspects.

In this article, we’re going to cover exactly whether you can use an extension cord with your space heater and what you have to be cautious of.

Question: Can I use an extension cord with a space heater?

Answer: No, you should not use an extension cord with your space heater. Most extension cords can not handle the high currents space heaters draw. Especially small, low-quality extension cords can easily catch fire. Don’t risk your home!

On top of that, there are additional downsides aside from the risk of melting and fire. Let’s cover them in a little more detail.

Can I use an Extension Cord with a Space Heater?

In this section, we’ll take a look at all the downsides of running a space heater with an extension cord. 

“You should never plug a heater into a power strip. These units are not designed to handle the high current flow needed for a space heater and can overheat or even catch fire due to the added energy flow.”

Umatilla County Fire District #1 in Hermiston, Oregon

Here’s some more explanation:

Extension cords usually can’t handle high current

Extension cords are oftentimes meant to handle lower amounts of current.

Medium-sized space heaters draw around 1,500 watts and 12.5 or more amps. That is what most extension cords can barely handle. The rating for your extension cord could be anything between 10-15A.

It’s like you’re walking on the edge of a cliff. Even slight fluctuations in power can cause your cable to burn.

On top of that, even if you have a cable rated at 15A, these high amounts of current can significantly heat the insulation and cause it to meld.

Most extension cords are not suited for space heaters.

Someone can trip over long cable

Having a long extension cord in your home also increases the chance of someone tripping over it.

If you have kids or pets at home, it is just a matter of time when someone trips over the cable.

This might not be harmful to the person tripping over (although it definitely could), but your space heater is likely to tip over.

Your space heater is likely to fall over and cause damage

When someone falls over the extension cord, your space heater could fall over.

This could cause damage by the impact of hitting the floor and might even burn or melt something.

Modern space heaters have tip-over protection that shuts off the heat when it tips over. However, as long as the heater hasn’t cooled down yet, it can still burn something.

Pay special attention to older heaters that don’t shut off. When they fall over on your carpet they can leave visible black burned stains that you can’t clean.

Extension cords lower the efficiency

When it comes to space heaters, efficiency is really important: You want to get the most heat for the least cost.

Heaters rely on having a strong power source that supplies them with lots of energy. If you interpose a long extension cord between your space heater and your wall plug, you effectively increase the resistance for the flowing current.

The nature of our modern power supplies is that they increase the power as needed. When you plug in an extension cord, power supply essentially has to increase the power in order to reach the space heater.

Even though this is just a tiny effect, extension cords might increase your electric bill in the long run.

Extension cords increase currents

When you use an extension cord, the resistance of it causes a voltage drop. This voltage drop is compensated by your power supply by delivering higher currents.

Remember: Your space heater will draw 1500W, no matter what.

Power equals voltage multiplied by current. This means that the current has to increase.

These higher currents can cause a fire! This is one of the main reasons you should never use extension cords.

Can I use a Power Strip with a Space Heater?

Similar to extension cords, you should not use power strips with a space heater. Power strips can easily heat up so the material melts. They might even catch fire.

Using power strips can be even more dangerous than using an extension cord in case you have more devices than just your space heater plugged in.

The more devices you run with the power strip, the more power is used. But a space heater already runs at the limit of what your power strip can deliver.

This means that the risk of a fuse melting or the cable overheating is even bigger than for regular extension cords.

Tips for using a space heater with an extension cord

“Between 2011 and 2015, portable and stationary space heaters accounted for more than two of every five (43 percent) U.S. home heating fires and five out of six (85 percent) home heating fire deaths.”

National Fire Protection Association

Half of all home heating fires were caused by running heaters too close to other things such as furniture or clothing. So, pay attention to where you run your heater.

If you absolutely need to use an extension cord, here’s what you should do:

Use a space heater that can switch between 750W and 1500W. Oftentimes, modern space heaters have the ability to limit their power usage.

With an extension cord, you should always run your space heater at 750W.

Lower power means the risk of damaging your power supply decreases. All regular extension cords can safely handle 750W.

When you run your heater at 750W, the increase of current caused by the extension cord will not harm your cable because it’s still well within the boundaries.

Also, always use the space heater in your presence. This will avoid dangerous accidents that happened in the past, where people left their space heater unattended and lost their home due to a fire.

How to tell whether your extension cord is safe

If you run your extension cord with too much power (e.g. a space heater that draws 1500 watts), here’s what usually happens:

Your cable heats up. Generally, the thinner your cable is, the hotter it will become. The reason is that with a thin cable, the amount of “current per diameter” increases.

Pressing a lot of current through a thin cable causes a big number of electrons to bump into the metal atoms of your extension cord. The atoms will then start wiggling around which causes heat.

Sadly, lots of the extension cords that look thick aren’t suited for high-power applications. Some extension cord manufacturers just use a lot of insulation to make it look thick and save money with thin copper wires.

A thick cable usually stays cool, because there’s more space for the current to travel.

warms up

Your fuse melts or your safety switch is triggered. Obviously, if you draw too much power from your house’s power supply, the fuse will melt in order to protect your power supply from more damage.

Heavy Duty Extension Cords

If you absolutely need to use an extension cord with your space heater, for example, when you want to heat a room that has no access to electricity, then I highly recommend getting a heavy-duty cord.

These cords are designed to handle the current that high-power devices draw.

Here’s the one I suggest using:

NamePriceWhere to find it
POWTECH Heavy duty 15 FT Major Appliance Extension Cord (Rated for 15A and 125V)under $10click here to see it on

Still, stay safe, even when you are using such a heavy-duty extension cord and preferably run your heater on low power settings.

The Outline: Can I use an Extension Cord with a Space Heater?

You should not use an extension cord with your space heater. There are just too many downsides to it.

For example, an extension cord will cause an increase in current that your power supply has to deliver. That’s why cables can easily overheat and catch fire.

Additionally, people can fall over the cable and tip over the space heater. And on top of that, the efficiency of your space heater is lowered.

However, if there’s no other option for you, you should definitely limit your space heater’s power demand to 750W or 1000W. Lots of modern space heaters have this capability.

Even though heating your room will take a little longer, this is a much safer approach than running your heater at full power.

About the Author

Daniel Hirsch

Daniel is an electrical engineer, blogger, and author. He studied electrical engineering and information technology and decided to blog about heaters after working in the temperature sensing industry.