How Many BTU is a 1500 Watt Heater?

The BTU of a space heater is important because it tells you if the unit is powerful enough to heat the space you plan to use it in.

A 1500-watt heater, the most common space heater size, puts out about 5118 BTU of heat. This is enough to heat about 170 square feet. But this number is based on average conditions.

Below, we’ll look at how to calculate BTU for a range of different-sized space heaters. We’ll also look at how BTU relates to room size coverage so you can find the right size heater for your room based on your needs and climate.

Watts to BTU Conversion Calculator

A BTU calculator is the easiest way to figure out how many BTU your heater puts out based on the wattage of the unit.

To use this electric heater BTU calculator, simply input the wattage of your space heater in the box below. The calculator will automatically calculate the BTU (British Thermal Units) of the unit.

Technically, this calculator gives you the BTU per hour (BTUh) rate for your unit. This is because wattage is a measure of rate while BTU is a measure of heat. To convert from one to the other, we must transform BTU into a rate measurement.

But for simplicity’s sake, we can look at this calculation as simply telling us the BTU output of the heater.

Watts to BTU Conversion Chart

Another easy way to figure out how many BTU your unit puts out is to reference our BTU conversion chart. 

To make this chart even more helpful, we’ve included information on room coverage associated with each BTU output. 

How much heat it takes to warm a room of a given square footage depends on how cold it is outside, how well the home is insulated, airflow, and many other factors. In general, you will need between 30 and 60 BTU per square foot to warm any given space.

To use this chart:

  1. simply locate the wattage of your heater and reference the BTU output
  2. The associated room coverage calculations tell you what size room the unit will work in for both average conditions and very cold conditions.
WattageBTURoom Coverage - Average ConditionsRoom Coverage - Very Cold Condition
10034111 sq ft6 sq ft
20068223 sq ft11 sq ft
300102434 sq ft17 sq ft
400136545 sq ft23 sq ft
500170657 sq ft28 sq ft
600204768 sq ft34 sq ft
700238880 sq ft40 sq ft
800273091 sq ft45 sq ft
9003071102 sq ft51 sq ft
10003412114 sq ft57 sq ft
11003753125 sq ft63 sq ft
12004094136 sq ft68 sq ft
13004436148 sq ft74 sq ft
14004777159 sq ft80 sq ft
15005118171 sq ft85 sq ft
20006824227 sq ft114 sq ft
300010236341 sq ft171 sq ft
400013648455 sq ft227 sq ft
500017060569 sq ft284 sq ft
600020472682 sq ft341 sq ft
700023884796 sq ft398 sq ft
800027296910 sq ft455 sq ft
9000307081024 sq ft512 sq ft
10000341201137 sq ft569 sq ft
11000375321251 sq ft626 sq ft
12000409441365 sq ft682 sq ft
13000443561479 sq ft739 sq ft
14000477681592 sq ft796 sq ft
15000511801706 sq ft853 sq ft
16000545921820 sq ft910 sq ft
17000580041933 sq ft967 sq ft
18000614162047 sq ft1024 sq ft
19000648282161 sq ft1080 sq ft
2000682402275 sq ft1137 sq ft

Manual Watts to BTU Calculation

watts to BTU formula

Electric heaters are nearly 100% efficient in turning BTU input into BTU output. This makes manually calculating BTU for electric heaters quite simple. All you need to do is multiply the wattage of the unit by 3.412, as demonstrated by this equation:

Wattage * 3.412 = BTU

For example, a 1,500-watt heater multiplied by 3.412 gives us a BTU of 5,118.

Alternatively, you can find the wattage of the heater you need based on the BTU required to heat the space using this equation:

BTU/3.412 = Wattage

How many BTU you need to heat a given space depends on how cold it is outside and how well-insulated the room is. 

In general:

  • Moderate temperatures outside require 30 BTU per square foot for adequate heating
  • Cold temperatures outside require 45 BTU per square foot for adequate heating
  • Very cold temperatures outside require 60 BTU per square foot for adequate heating

If your home is poorly insulated you will need more BTU per square foot for adequate heating.

Once you know how many BTU you need to heat your room, you can use this calculation to find out the optimal wattage for your new heater:

(Optimal BTU * Room Square Footage)/3.412 = Wattage

As we discussed above, wattage is a rate measurement and BTU is a simple heat measurement. This means that technically you need to convert BTU to a rate measurement to move between the two units. 

The number 3.412 allows us to do this as it represents the number of BTU a single watt puts out every hour.

In the above equations, we have simplified BTU somewhat. To get a full understanding of what this measurement represents and how it is used to calculate different heat and air conditioning needs, check out this article.

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Sara Seitz
Sara Seitz is a freelance writer and novelist. She lives with her husband and wildling toddler in Colorado where she spends her days working on their house, gardening, and reconnecting with nature.

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