What Guage Extension Cord Is Suitable for Electric Heater

Josh Mitchell

Written By

Josh Mitchell

Expert Reviewed By

Holly Curell

Last Updated On

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Key Takeaways

  • The gauge size of the extension cord depends upon the input current or the input power requirement of your heater.
  • Always use a heavy duty extension cord with a space heater that carry MORE than the required amperage. 
  • Observe safety precaution when using space heater such as not using a very long cable, not daisy chaining multiple extension cords, and not using multiple appliances over the same cord.

I don't need to tell you how incredibly dangerous electrical fires are — many of which are caused by those who don't know how to use an extension cord correctly.

So, what’s the solution? I'm here to show you how to use heavy-duty extension cords with your electric heater so it's NOT overloaded and has plenty of power supply.

Here’s what to look for when shopping for a gauge extension cord for your space heaters.

What Exactly is American Wire Gauge?

Basically, the American Wire Gauge tells you the size of the wire and its current carrying capacity — how much power it can safely handle.

In most cases, using an extension cord with a space heater is not recommended.

However, using this measuring system, we can choose a heavy-duty extension cord with a thicker wire that can handle the higher power capacity required by a space heater.

Useful Note:

Counter intuitively, the lower the AWG, the larger is its with and current carrying capacity. In other words, a lower wire gauge number indicates a thicker extension cable.

This factor is INCREDIBLY important because any extension cord that feels hot to the touch can be a fire hazard. Unplug the cord immediately.

Circuit Amperes for Different Wire Gauges

TL;DR: AWG is a standard for electrical cable size mostly used in US. The AWG relates to the thickness and the current carrying capacity of an electrical cable.

What Gauge Extension Cord Is Best For An Electric Heater?

There are two ways I recommend assessing your gauge extension cord for this mammoth task:

  1. 1
    Checking the gauge of the heater’s power cord
  2. 2
    Looking at wire sizing (evaluating the size of the extension cord and the size based on the input current).

Let’s take a deep dive into these two methods so you can pick the best extension cord to power your space heater.

Look at the Gauge of the Heater’s Power Cord and Size Extension Cord

Remember, the lower the gauge, the higher the electrical rating.

So, a lower gauge cord is better with a space heater as long as it's a heavy-duty extension cord that can handle the heat (read: don’t purchase a flimsy, cheap extension cord).

Also, shop for a short, heavy-duty extension cord with a thicker wire.

Not only does this reduce the chances of tripping, but it avoids messy voltage drops (more on this later).

Regarding size, space heaters usually average around 1500 watts of power, equivalent to 14 amps, when you connect it to a traditional 110-volt outlet.

When shopping for an extension cord for a 1500-watt heater (or one with any other power rating), look for one that can provide this power rating.

For example, a small space heater usually needs a minimum gauge of 14.

Size Based on Input Current

Look up the specs of your electric heater and search for input wattage.

The input wattage indicates how much wattage (power source) your electric heater needs to operate effectively.

Without enough wattage, the space heater may fail or overload the extension cord (leaving you with expensive repair costs or the potential risks of fire!)

As you're examining the specs, you may notice that your space heater's output has a different rating than the input.

This discrepancy is because machines aren’t perfectly energy efficient and have energy losses.

For example, a heater may have a 1500W output rating but will have a higher input rating and higher input amperage requirement to achieve this.

Think of it this way — when you put gas in your car, it doesn’t convert 100% of the fuel energy into working energy. A lot of that energy is lost as heat. This is the same situation.

So, what does this mean for you?

Essentially, you need to check that you are supplying your electric heater with enough input wattage, aka power source (ideally with a 20% safety margin), to safely use a gauge extension cord with an electric heater and meet the necessary power requirements.

A thicker wire also indicates better insulation, meaning it won't generate heat and risk an electrical hazard.

Having enough input wattage with a safety margin reduces potential risks like fire and keeps your space heater running smoothly.

Useful Tip:

You can search up your space heater's make and model online to figure out its required input power or input current rating.

Key Specs for Heatstorm

TL;DR: Look at the gauge of the heater's power cord or look at its power/amp rating to determine the correct extension cord gauge size.

Why Is Sizing the Extension Cord Gauge So Important?

The length and gauge of the extension cord make a HUGE difference in how the cord performs.

If your cord isn’t the right size or gauge, you can quickly damage your electric heater or extension cord, or either device could catch fire.

I am here to help you choose an appropriate extension cord that can actually handle your electric heater so you don’t end up like the roughly 3,300 homes that experience fires originating from extension cords — almost always because the cord is used incorrectly or is overloaded from power-sucking appliances like space heaters.[1]

The Wrong Extension Cord Can Trip Breaker

I don’t know about you, but the last thing I want on a frigid, dark winter night is to lose the use of my space heater and have all my lights turned off — stumbling around in the dark, trying to get the lights turned back on is not exactly the cozy night-in I was looking for.

Tripping the breaker means using too much power from the circuit. 

Basically, there isn't enough power supply to support everything you currently have plugged in,

If you’re looking around and spot multiple space heaters, power strips, heating appliances, kitchen tools, and other electronics you have plugged in simultaneously to the same circuit, try unplugging some to reduce stress on the breaker.

While our homes are designed to handle multiple appliances' power requirements, stressing the entire electrical system with a parade of power-sucking appliances simultaneously poses electrical hazards and can cause something to catch fire.

Look For Clues Of Malfunctioning

Suppose your electric heater isn't functioning properly when plugged into your extension cord. In that case, this is an immediate clue that the strip may be overloaded or damaged.

Immediately unplug it and check the extension cord’s gauge and size to see that it’s appropriately matched to your heater.

If you’re convinced it is, examine both the extension cord and heater for any signs of damage.


If you suspect the extension cord is not powerful enough or damaged, try plugging the heater directly into an outlet and see how it functions.

This step can help you determine if the extension cord is the issue or the heater is malfunctioning.

TL;DR: A weaker (thinner) cable then necessary will get hot and can even burn. This can trip the breaker at best and pose fire hazard at worst.

How To Safely Use Gauge Extension Cord To A Space Heater

The second (and often overlooked) part of using a gauge extension cord with an electric heater is learning how to use an extension cord correctly.

Now, you may be looking at the screen, thinking, how do you mess up plugging a space heater into an extension cord?!

I'm here to tell you that you'd be surprised how many ways you can actually mess up how to use an extension cord with your space heater.

And, since a space heater requires a significant power supply, you really don’t want to mess this up and put your home at risk of an electrical fire, so keep reading to avoid these seven common safety mistakes.

1. Make Sure the Receptacle Has Sufficient Amperage Rating

If your space heater has a 15 amp rating, the extension cord and receptacle need to have AT LEAST a 15 amp rating.

If one has less, the entire set-up is at risk of overheating because it doesn’t have the amps required to run properly.

Think of it this way — if your home has eight-foot ceilings and you try to set up a ten-foot Christmas tree, you’re going to be left with a squished, unfortunate-looking tree that ends up scratching your lovely ceiling up, or worse, toppling over onto your curious cat.

Don’t try to make a receptacle with insufficient amperage ratings work.

It’s not worth the potential RISK of starting a fire in your home, endangering you, your family, pets, and personal property.

TL;DR: Not just the cable, but the receptacle should also have sufficient amperage rating. 

2. Have a Safety Margin of 20% Higher Amperage Capacity

Don’t toe the line by using extension cords that match the minimum requirements. Use a heavy duty cord with enough safety margin to keep yourself safe.

This is an area where "overachieving" by using a heavy duty extension cord with a safety margin of at least 20% is absolutely necessary.


Having the amperage safety margin for the circuit is also important. In other words, if you have a space heater rated at 15 amps, it is best practice to use it on a 20 amp circuit.

TL;DR: Always have at least 20% safety margin on both the extension cord and the receptible in terms of amperage rating.

3. Make Sure Extension Cord Are Not Too Long

A long extension cord requires a higher gauge extension cord (read: more expensive, so no cheap extension cords).

If the extension cord is too long, you can also experience a voltage drop, meaning you have less voltage available to you at the socket of the extension cord than what the entire socket outlet could provide you.

Since space heaters use a lot of power, this is a big problem that will leave you shivering down to your long underwear when the space heater fails or requires significant repairs.

Generally, your voltage drop shouldn't exceed 5%, so stick with shorter cords with ample amps and insulation to avoid this issue.

For practical reasons, a long extension cord can also be a tripping hazard, which you don’t want to risk, especially if you end up yanking your space heater down with you (another reason that anchoring your space heater is VERY important).

The point is that you want to purchase the shortest extension cord possible with the amps necessary (plus a safety margin of at least 20%) to minimize the risk of voltage drops, fire, and tripping.

TL;DR: Too long extension cord will result in voltage drop. This can lead to more current draw from the receptacle to compensate leading to breaker tripping. 

4. Use Extension Cord from Well Reputed Brands

Don't just waltz into a home improvement store and pick up one of the first generic, regular extension cords you see.

These cheap extension cords lack insulation and other important safety features.

Saving a few dollars by buying a cheap extension cord isn't worth the risk to you and your family's safety.

Take your time and research extension cables from several reputable brands before selecting one. I prefer the US Wire & Cable brand.

TL;DR: Do not cheap out on the extension cord quality ESPECIALLY if it is to be used with a heating device like a space heater.

5. Make Sure They Have Safety Features

Before buying, double-check that your extension cord has a large plug face and grip for easy removal (improper removal causes TONS of damage to the outlet and cord), fuse protection, safety closures, and sufficient insulation to prevent shocks, and has been tested by a national testing laboratory.

Important Note:

Regularly inspect your extension cords for signs of wear and tear. Frayed wires or damaged plugs are immediate signs that you should replace the cord as the insulation is no longer effective. Touching one exposed strand on a cord can result in electric shock or burn.[2]

TL;DR: Extension cords can come with different type of safety features like fuses, overcurrent and surge protection etc. The more safety features it has the better.

6. Do Not Use a Plug Adapter

Per the University of Montana and the Office of Risk Management (with a name like that, we better listen), extension cords shouldn’t be used with multi-plug adaptersAt all.[3]

This increased cord length puts you at a much higher risk of electrical resistance, leading to more heat generation and a higher chance of your power strip catching fire.

7. Avoid Daisey Chaining Extension Cords

Again, MAJOR fire risk. I don’t need to explain how scary house fires are, but this is your reminder not to “daisy chain” multiple extension cords.

The only connection your power strip should have is your wall outlet.

TL;DR: Avoid plug adapter or daisey-chaining extension cords. The risk they carry is simply not worth it.

Common Questions Asked (FAQs)

Should You Even Use Space Heaters With An Extension Cord?

You shouldn't use most space heaters with an extension cord as a general rule unless you take precautions to ensure the power strip has sufficient amperage ratings and isn't long enough to become a tripping hazard or experience voltage drops.

Can You Plug An Oil Heater Into An Extension Cord?

No, you shouldn’t plug an oil heater into an extension cord because extension cords don’t typically have a high enough current flow to meet the oil heater’s electrical needs.


  1. https://www.esfi.org/reaching-to-safety-use-extension-cords-properly/
  2. https://www.esfi.org/extension-cord-safety-tips/
  3. https://www.umt.edu/risk-management/safety-compliance/safety-fact-sheets/extension-cords.php
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Josh Mitchell


Josh Mitchell
My name is Josh and I am obsessed with home appliances. From portable AC units to heaters and air purifiers, I enjoy testing, learning and using these devices to improve the air quality inside my family home.

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