It’s quite easy to calculate how many amps does a space heater use. You will need to know that for wiring, breaker sizing and generator sizing. We will explain how to figure out how many amps does any electric heater draw.
Further on, you will find:
- Heater Amps Calculator (just insert wattage and voltage, and get the amps),
- Amp Draw Chart for 100W to 20,000W heaters.
- Solved examples for 750 watt, 1500 watt, and 5000 watt heaters.
Here is the most basic example:
How many amps does a 1500 watt heater draw?
We use a simple electric power equation and express I (current, measured in amps):
P = I × V or I = P / V
To get the heater amp draw, we only need to divide power input (wattage) by voltage. In the case of a 1500W 120V heater, the calculation looks like this:
I (Amp Draw Of 1500W Heater) = 1500W / 120V = 12.5 Amps
As you can see, a 1500W heater draws 12.5 amps. That means that we can use a 15A or 20A breaker to put one of such heaters on. If you have a 30A breaker, you can even put two 1500W heaters on that circuit. You also need at least a 15 amp generator to run a 1500 watt heater.
Note: Most often, heaters with up to 1500W use 120V circuits. More powerful 1500W+ heaters use 240V circuits. Check the amp draw chart below to see the exact amps of different sizes of space heaters.
To simplify this calculation, we have prepared Heater Amps Calculator. We have also calculated amp draws of all space heaters from the smallest 100 watt panels to the big 20,000 watt 240V heaters. Be sure to check out the examples further on that specify how the amp draw changes if you plug a 1500W heater into a 240V GFCI outlet (doubling voltage halves amps draw):
Heater Amp Calculator
Here you just insert wattage and voltage, and the calculator will automatically tell you how many amps does such a heater draw:
Here is a good example of how to use this amp draw calculator:
Let’s say you have a 1000 watt heater on a 120V circuit. How many amps does such a heater draw? Just slide the 1st slider to ‘1000’ and the 2nd slider to ‘120’ and you get the result: A 1000W 120V heater draws 8.3 amps.
If you have an upgraded 240V circuit, the 1000 watt heater will draw fewer amps. If you slide the 2nd slider to ‘240’, you can see that the 1000 watt heater amp draw is lowered to 4.2 amps.
This is just a 1000W example. Let’s have a look at electric space heater amp usage of all heater sizes:
How Many Amps Does A Heater Draw? (Chart)
In this chart, we have calculated the amp draws for all heaters; from the smallest 100 watt electric panels to big 20,000 watt heaters. Do note that smaller heaters (1500W or smaller) are usually connected to a 120-volt circuit. Bigger heaters (more than 1500W) use a 240-volt circuit. The relevant amp draws in the chart are marked in bold text:
|Heater Size:||120V Amp Draw:||240V Amp Draw:|
|100 Watts||0.8 Amps||0.4 Amps|
|200 Watts||1.7 Amps||0.8 Amps|
|300 Watts||2.5 Amps||1.3 Amps|
|400 Watts||3.3 Amps||1.7 Amps|
|500 Watts||4.2 Amps||2.1 Amps|
|600 Watts||5.0 Amps||2.5 Amps|
|700 Watts||5.8 Amps||2.9 Amps|
|800 Watts||6.7 Amps||3.3 Amps|
|900 Watts||7.5 Amps||3.8 Amps|
|1000 Watts||8.3 Amps||4.2 Amps|
|1250 Watts||10.4 Amps||5.2 Amps|
|1500 Watts||12.5 Amps||6.3 Amps|
|2000 Watts||16.7 Amps||8.3 Amps|
|3000 Watts||25.0 Amps||12.5 Amps|
|4000 Watts||33.3 Amps||16.7 Amps|
|5000 Watts||41.7 Amps||20.8 Amps|
|6000 Watts||50.0 Amps||25.0 Amps|
|7000 Watts||58.3 Amps||29.2 Amps|
|7500 Watts||62.5 Amps||31.3 Amps|
|8000 Watts||66.7 Amps||33.3 Amps|
|9000 Watts||75.0 Amps||37.5 Amps|
|10000 Watts||83.3 Amps||41.7 Amps|
|12500 Watts||104.2 Amps||52.1 Amps|
|15000 Watts||125.0 Amps||62.5 Amps|
|20000 Watts||166.7 Amps||83.3 Amps|
As you can see from this table, for heaters with up to 1500W 120V, you can expect an amp draw of 12.5 amps or lower. That means that you can use standard 15A breakers.
For bigger heaters, you have to check the 240V amp draw column. 30A breaker will handle anything up to 6000 watts (25 amp draw). Be mindful that the 30A breaker is too small for a 7000 watt heater despite the 29.2 amp draw.
Amp breakers should never surpass 80% of their maximum ampacity, according to the NEC guidelines. That means that a 30A breaker can at most handle 25 amps.
For bigger 10000+ watt heaters, you will need two or even three 30A breakers.
Let’s look at 3 heaters with 750W, 1500W, and 5000W power to see how many amps they draw and what size breakers you may need:
How Many Amps Does A 750 Watt Heater Draw? (Example 1)
750 watt heater is a small heater that can produce 2559 BTU of heating output. This is enough to heat up spaces up to 85 sq ft, if we use 30 BTU per sq ft of living space rule of thumb. How many amps does a 750 watt heater draw?
We usually plug a 750 watt heater into a standard 120V circuit:
- A 750 watt 120V heater draws 6.3 amps.
- A 750 watt 240V heater draws 3.2 amps.
Even if you have the smallest standard 15A breaker, you can connect two 750W 120V heaters on it.
How Many Amps Does A 1500 Watt Heater Draw? (Example 2)
1500 watt heater is a small heater that can produce 5118 BTU of heating output. This is enough to heat up spaces up to 170 sq ft, if we use 30 BTU per sq ft of living space rule of thumb. How many amps does a 1500 watt heater draw?
We usually plug a 1500 watt heater into a standard 120V circuit:
- A 1500 watt 120V heater draws 12.5 amps.
- A 1500 watt 240V heater draws 6.3 amps.
That means that you can connect only one 1500 watt 120V heater to a 15A breaker.
How Many Amps Does A 5000 Watt Heater Draw? (Example 3)
5000 watt heater is a small heater that can produce 17,060 BTU of heating output. This is enough to heat up spaces up to 570 sq ft, if we use 30 BTU per sq ft of living space rule of thumb. That’s why these heaters are very useful 240V electric heaters for a garage. How many amps does a 5000 watt heater draw?
We usually plug a 5000 watt heater into an upgraded 240V circuit:
- A 5000 watt 120V heater draws 41.7 amps.
- A 5000 watt 240V heater draws 20.8 amps.
A 30A breaker can handle a 5000 watt 240V heater.
Hopefully you now understand how to calculate heater amp draw and you know a thing or two about which breaker size to use. If you have any questions regarding how many amps your space heater uses, you can use the comment section below and we’ll try to help you out.
Table of Contents