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Meaning of Delta 50 (75/65/20) 

Delta 50° (75/65/20) - with Delta T of 50°C, means 75°C inlet water temperature, 65°C outlet water temperature and 20°C of room temperature. The average water temperature in this example is 70°C (i.e. 75° plus 65°, divided by 2).  If we then take the 20°C room temperature we are left with a temperature differential of 50°C or Δt 50°.  

Method - 

Add the flow water temperature and the return temperature together

Divide the answer by 2

Subtract the room temperature from the answer this gives you the Delta T temperature

Select the closest Delta T valve from the table and multiply the corresponding factor by the output provided for the particular radiator to obtain the output for your calculated Delta T valve.

When comparing products ensure you are being quoted Delta T 50°, furthermore look for the MARC logo (Manufacturers Association of Radiators and Convectors) and be sure to request the Declaration of Performance, conducted by an accredited body. 

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. The above calculator has been designed to efficiently calculate this based on input at Delta T 50°, alternatively, you can use the listed correction factors below, also based on Delta T 50°.

Example: Assuming a radiator or towel rail has a heat output of 1000 Watts at ΔT (Delta T) = 50°. At ΔT (Delta T) = 60°, the output would be 1000 x 1.27 (from the table above) equating to 1270 Watts. Alternatively, at ΔT (delta T) = 40°, the output would be 1000 x 0.75 equating to 750 Watts.