Can You Run a Space Heater Off a Car Battery

To run a space heater off a car battery makes sense in two cases: When you camp in a freezing cold car, or during an energy outage.

In this article, we're going to cover everything you need to know about whether you can power a space heater off a car battery when there's no other energy source around!

In an emergency survival situation, you'll try everything you can to stay warm. So, is it a practical solution to connect a space heater to your car battery? I'm an electrical engineer, and I'll show you how it would work!

Question: Can you run a space heater off a car battery?

Answer: Yes, you can run a space heater off a car battery. You would need to convert the DC current to AC first and then transform it to 120V. So, in theory, it's possible. But can a car battery handle such loads? And how long would it last? And are there better ways to stay warm?

Let's answer all these questions:

At the end of this article, I'll give you a much better alternative for heating than trying to run a space heater off your car battery.

How much power does a space heater need?

Most space heaters in the US need about 1500W of power. That's quite a lot. Most space heaters draw 12.5 amps.

Heaters are among the household devices that need the most power.

Here's what the Ohio State University says:

"While any amount of current over 10 milliamps (0.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA (0.1 to 0.2 amp) are lethal."

Ohio State University – Physics

Now, if 0.1-0.2A are lethal already, think of what 12.5A can do.

Heaters need a lot of power.

Here's another example:

"A climber who raises his own body weight (say 70 kg or 154 lb) by moving up a slope of 10 meters (33 feet) vertical height in one minute is working at the rate of 0.15 horsepower or 114 watts"

American Alpine Club

That means that 1500W, the power a space heater needs to run, would equal the power you need to climb 132 meters (433 feet) vertically in a minute.

Can you run a space heater off a car battery?

If you want to run a space heater off a car battery, you first need to know how much power a car battery can deliver.

"A standard small car battery is about 45 ampere-hours. That means that it will supply over two amps for 20 hours. A battery should not be discharged at a higher current draw, or asked to deliver more amps than its amp/hour rating divided by 10"

UH Manoa Chemistry Department

If short-circuited, car batteries can deliver up to 300A (caution: extremely dangerous). So, they are capable of producing 12.5 amperes of current for a space heater. However, according to what the quote above says, you shouldn't discharge a car battery at a higher current draw than it's rating divided by 10.

For a 45 ampere-hour battery, that would mean you should keep the discharge rate below 4.5A to keep the battery healthy. But most space heaters require 10-15A.

But in an emergency situation, where you need to keep warm, you don't care about that rate. So, theoretically, a car battery can produce enough energy to run a space heater.

Note: This is just a theoretical result. We'll cover whether it makes sense later on. There's a lot more to keep in mind.

You would need an inverter and a transformer

Car batteries only deliver DC current. Household space heaters need AC. So, you would need to install an electrical inverter (a device that transforms DC to AC).

Additionally, car batteries have a voltage of 12V, whereas a space heater needs 120V (or 240V in Europe). For increasing the voltage, you'd need to use a transformer.

To connect and run a space heater off a car battery, you'd need to connect the space heater to a transformer, the transformer to an inverter, and the inverter to the battery. To me, that sounds like a big hassle. Especially if you're unfamiliar with electronics.

And it's dangerous as well.

How long would a car battery last with a space heater?

Let's assume that you have a car battery with a capacity of 45 ampere-hours. A regular space heater draws 12.5A. That would mean your car battery would last for 3.6 hours with a space heater.

And we didn't even account for the energy losses of the inverter and transformer.

Still, the 3.6 hours are more than I initially expected. Car batteries can store huge amounts of energy because they consist of many smaller battery packs that are connected to each other.

To me, that's an impressive result.

Downsides of powering a space heater with a car battery

This is going to be the most important part of this article. We're going to cover whether it actually makes sense to power a space heater with a car battery. Let's take a look at all the risks and downsides:

• High current draw puts stress on car battery: The high amount of current your space heater needs puts a lot of stress on your space heater. If you remember what we talked about before, you shouldn't pull more than 4.5A from a car battery. A space heater easily surpasses this limit. Your car battery is likely to overheat and get permanently damaged.
  Connecting a space heater to it would put the same stress on your battery as cranking the engine continuously (for hours)!
• Risk of damage: You simply shouldn't play around with such high current devices. Car batteries and space heaters are a dangerous combination. Especially when you accidentally connect something the wrong way.
• Drain battery: In an emergency, it might be a better decision to use your car battery to drive somewhere instead of using it to produce heat.
• Cars have poor insulation: This, of course, only applies if you use the space heater in a car. Cars usually have poor insulation and the heat will quickly disappear. Heating in a car is incredibly inefficient.

Alternatives for keeping warm in an energy outage

There are some alternatives for keeping warm when you don't have access to electricity that you need to consider before even thinking about using a car battery.

Car space heaters

There are car space heaters that are specially made for cars. You can directly connect them to your car battery. Usually, they are smaller than regular space heaters, but they are just fine for keeping the temperature up in a car.

At home: Indoor propane heaters

For heating a home without electricity, the very best way I know of is using an indoor propane heater. One 20lb propane tank can keep your room warm for up to a week! When I reviewed whether you can use a generator to power a space heater, I also concluded that propane heaters are a safer, more efficient and more durable method to keep warm without electricity.

Here's the propane heater I recommend (click here to check the price on amazon).

Conclusion – Can you run a space heater off a car battery?

Answer: Yes, with a little technical know-how, you can run a space heater off a car battery. But you shouldn't! Even though it might work, you will permanently damage your car battery. Additionally, it will only keep you warm for around 3 hours until the battery is drained and it's dangerous as well (you're playing with high current devices).

Instead, you should get an indoor propane heater to keep warm in an energy outage. One 20lb propane tank will keep you warm for a week. It's just a much wiser choice.

I hope this article could help you! If you're interested, check out all the other home heating articles!

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.

Can You Run a Space Heater Off a Car Battery

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