How Many Amps Does a Space Heater Use?

Space heaters are an excellent source of heating for people who live in colder areas. You can use them to provide warmth in your home, office, or other location that needs additional heat during the winter months.

However, it is important to know how much power a space heater uses before purchasing one. This post will discuss the amps per hour (A/H) usage of different space heaters and help you find the right one for your needs.

Typically, a space heater with a 1500-watt rating (on high) consumes 12.5 Amps. However, the 15 Amp restriction is soon reached when several lights or television are on the same circuit, and the breaker will trip.

What Are Amps?

Amp is a unit of electric current. It measures how much electrical power can flow through an electronic device at any given moment. 

An amplifier converts the voltage from one level to another. Therefore, it provides higher output than input, which means that amps are used as units for measuring electrical power or work done on units of charge (for example, in electromagnets). 

The term “amps” was first coined by James Watt to compare the amount of water needed to turn his new steam engine with horses.

Space Heater Amps for Different Space Heater Sizes in BTU

A space heater between 500-1000 BTUs will use somewhere in the range of 1500 to 4000 watts, or up to six amps. This means it would take about an hour for this small heater to drain a fully charged car battery. If you are looking at larger heaters of over 5000 BTUs, these units may draw closer to ten or twelve amps per hour on average!

How Many Heaters Can You Run on a 20 Amp Circuit?

The number of heaters you can run on a 20-amp circuit depends on your heater’s capabilities. Electric heaters can vary in power, so it is important to know how many amps a space heater uses before plug one into an outlet.

An electric water heater requires 30-40 amps and gas/oil furnaces require 50+ amps for proper energy efficiency. It’s best practice to contact a professional if you’re unsure about what size circuit breaker or wiring your home needs.

A space heater uses an average of 1500 watts, and a regular household outlet can only run up to 20 amps. This means that if you want to plug in more than one heater, they will need their dedicated circuit breaker. 

You can get away with running two heaters on the same circuit as long as each unit doesn’t exceed 1550 watts (1500W divided by 110V). If all your heaters add up to over 1550 wattage, then the total load cannot exceed what’s allowed for a standard house outlet which is 1800 watts or less. 

A 120 volt home electrical system would also be unable to power three units exceeding 2100 watts combined. Two 1275 watts plus one 1050 = 2925watts/120v = 25.83 amp. 

This means it’s over the 20-amp limit for a standard outlet, so they won’t work. However, if you plug all three heaters into their dedicated circuit breaker, it would be safe to power them since each heater wouldn’t exceed 1550 watts (1500W divided by 240V).

Can a 240V Heater Run on 120V?

Yes, a 240v heater can run on 120v. If the wattage is less than or equal to your home’s power distribution system (the total amps), it should work fine. However, you will not be able to use all of its heating capacity when running at half voltage. 

Think about how much current an appliance uses if you reduce the voltage in half—since Joules = Amps x Volts, halving either one halves your energy output by volume.

How Do You Calculate the Amperage of a Heater?

To find out how many amps a space heater uses, you can check the label on its body. However, this is not always an option as some heaters don’t come with such labels. In case there’s no label on it or if you want to be extra sure about your calculations, follow these steps:

Calculate the wattage of the device by multiplying volts and amps together. For instance, a 120 V space heater that requires 15 A would have 1800 W (120 * 15). Find the total number of watts required for heating purposes from manuals provided by manufacturers or online sources.

 As mentioned above, our example has 1800 W, so multiply them by 0.83, which will give 1440 BTU/h. Next, calculate the total number of amps required for heating purposes by multiplying watts and hours in use. 

1440 BTU/h equals 12,960 W * 0.83 (hours used), which would be approximately 11 A (129600 / 120). Therefore, add an extra 15% to this value as a safety measure.

How Do You Calculate Current in a Heater?

The current of a space heater is calculated using Ohm’s law, V=IR. Therefore, to solve the number of amps in your heater, you will need to know two things; voltage and resistance. 

The volts are provided by an electric company (i.e., 120v), while the resistance can be measured with a simple multimeter or assessed by looking at it (most heaters use between 12-14 ohms). 

After doing these calculations, you should have both the volts and watts required to calculate power, given that watt = volt x amp.

This formula works for most electrical devices; however, it is important to note that this number will not always be an exact calculation. For example, this can happen if the resistance changes due to heat or other factors such as age.

There are a few other factors that you will need to know to finalize the calculations. The first is whether or not your heater has a fan. If so, this will increase energy consumption by drawing more amps from an outlet, resulting in tripping breakers and blowing fuses. 

In addition, heaters with heating elements made of coiled wire (i.e., flat coil) draw about 15% more power than those with straight element coils because it takes less time to heat up, resulting in faster temperature rise times. 

While straight element coils take longer to get hot but once they do, they maintain their temperature better than coiled ones. This is regardless of how much current flows through them.

Heat Load Calculation

You will need to know the heat output of the space heater and the length of time you plan on using it. You can find this information from the manual or online for each specific model.

You mustn’t exceed this wattage as doing so may cause damage to either yourself, your home, or both.

There are a few different types of space heaters, and each has its unique considerations when it comes to power consumption:

Low wattage convectional units – these operate by heating air that’s drawn into the heater from outside, so they don’t require any electricity to run themselves. As such, you only need an outlet for them.

Low wattage radiant units – these heat objects (not the air like low wattage convectional units) are then radiated. They’re often more efficient than other types of space heating options, but they still do need to be plugged into a power source for them to work correctly.

High wattage convectional units – if your unit uses an electric resistance element behind its fan, it will require electricity even when not operated! These have higher energy consumption rates, so you’ll want to ensure that you don’t overload any circuits in your home or create issues with your breaker box by plugging too many high-watt devices on one circuit.

Here is a standard equation you can use:

Heat load (BTU) = Length (m) x Width (m) x Height (m) x 141. So, for a room measuring 5m 4m 3m 60, the equation is 8,460 BTU.

How to Size a Heater Circuit Breaker

The National Electrical Code (NEC) is a must-follow guide for sizing circuit breakers. To sum up the NEC, every space heater must be connected to its 20-amp breaker or fuse in your electrical panel. If you are using multiple heaters on one outlet, then know that it needs to have its 40-amp breaker/fuse as well.

Low Amp Space Heaters – Are They Worth It?

This is a very common question for homeowners, and it can be challenging to answer because there are so many factors that contribute to the amount of electricity used.

For example, if you choose an electric space heater with low wattage but high amperage ratings, this will use more energy than one that uses higher wattage at lower amperages. This is because wattage measures the power used by an appliance, while amps measure how much energy it uses at any given time.

It’s also important to note that space heaters are designed for temporary use – not constant heating, so you should still set your thermostat to a comfortable temperature during the day and only turn on your heater when necessary. Of course, if you live in cold and icy climatic or drafty areas, this may be more frequent than others.

Therefore, it all depends on your needs and whether you feel like using such a heater, judging by the information we’ve provided above.


Overall, the amps a space heater uses vary greatly. If the heater is over 1500 watts, it will use around 13 amps, and if it’s under that, it’s usually between nine and 12 amps. Remember to multiply this number by 120 volts for a rough estimate of how much power you are using every day.

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