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Radiator BTU Calculator

BTU or watt output needed to heat a room.

Enter your values

ⓘ Live results

Results
Heat output needed
5,376 BTU/hr
In watts
1,576 W
In kilowatts
1.58 kW
Room volume
1,344 cubic feet

Working

  1. 11,344 ft3 x 4 x 1 x 1 = 5,376 BTU/hr

Quick answer

Room heat requirement scales with volume and heat loss. This tool uses a volume factor adjusted for insulation, glazing and room type.

BTU = volume x factor x insulation x glazing

How to use the Radiator BTU Calculator

  1. 1Measure the room and enter its volume dimensions.
  2. 2Adjust for insulation quality and how much glass the room has.
  3. 3Match or slightly exceed the BTU figure when picking a radiator.

Worked example

Using the values the calculator loads with:

Inputs

  • Room length14 ft
  • Room width12 ft
  • Ceiling height8 ft
  • InsulationAverage
  • GlazingStandard
  • Room typeLiving room

Results

  • Heat output needed5,376 BTU/hr
  • In watts1,576 W
  • In kilowatts1.58 kW
  • Room volume1,344 cubic feet
  1. 1,344 ft3 x 4 x 1 x 1 = 5,376 BTU/hr

Frequently asked questions

Should I oversize a radiator?

A modest 10 to 15% margin lets you run lower water temperatures, which is more efficient with a condensing boiler or heat pump.

How do I convert BTU to watts?

Divide BTU per hour by 3.412. A 5,000 BTU/hr radiator is about 1,465 watts.

About this calculator

Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.