BTU Calculator

BTU or British Thermal Unit - is the amount of heat needed to increase the temperature of 1lb (one pound) of water by one degree Fahrenheit. This is the imperial measurement, your Installer may work using metric values for this calculation; Watts. Either can be used to choose your radiator.

With radiators, the BTU measurement refers to how much energy is required to heat a room. The higher the BTU is, the greater the radiator’s heat output will be. How effective the radiator will be though, depends on factors such as the size of the room and how well insulated it is. A radiator’s ability to transfer heat will depend on its material, size and surface area as well as the water temperature within the system.

Delta T, or ∆T, specifically relates to the difference in temperature between the water circulating in the central heating system and that of the room or ambient temperature.

Flow in 90°C ,Flow out 70°C = Average water temperature inside radiator is 80°C.

If the room or ambient temperature is 20°C and the average water temperature inside the radiator is 80°C, the Delta T or ∆T value is calculated as 80°C - 20°C = 60°.

A Delta T correction factor allows end users and professionals to find out the actual output of a radiator or towel rail in the range of Delta T variations.

Eastbrook provides Delta T 60° outputs. You can use the listed correction factors below to find the actual output at Delta T 50° and other Delta T’s listed below:

ΔT	Correction Factors
60°	1
55°	0.901
50°	0.781
45°	0.699
40°	0.599
35°	0.513
30°	0.424
25°	0.338
20°	0.256
15°	0.179

Example: Assuming a radiator or towel rail has a heat output of 750 Watts at ΔT (delta T) = 60°. At ΔT (Delta T) = 50°, the output would be 750 x 0.781 (from the table above) equating to 585.75 Watts.