After you have worked out the heat requirement for your room (AEL's easy-to-use BTU calculator will help you do this), how can you check that the radiator you have chosen will provide enough heat output?

There is a simple calculation to check if the radiator will provide sufficient heat output. You must check the “delta T”.

What is the "delta T"?

In the AEL radiator catalogue, a heat output figure is provided for each of the radiators, along with the radiator's dimensions. The heat output figure is reported for a specific "delta T". The delta T is the difference between a target room temperature and the average temperature of water in the radiator. The average temperature of the radiator depends on the temperature of the water entering and leaving the radiator, which may be different in your heating system.

delta T = (Room temperature) - (Average radiator water temperature)

If the delta T of your system is different from the one shown in the catalogue, then you will need to calculate a new heat output. This is easily done by multiplying the output figure in the catalogue by a correction factor.

Correction factor table

Delta T (°C) Correction factor
5 0.050
10 0.123
15 0.209
20 0.304
25 0.406
30 0.515
35 0.629
40 0.748
45 0.872
50 1.000
55 1.132
60 1.267
65 1.406
70 1.549
75 1.694

The diagram below illustrates a case where the desired room temperature is 20°C and the average water temperature across the radiator is 70°C. The difference, the "Delta T", is 50°C.

 

 

If the “Delta T” in the catalogue is 50°C, it is perfect to just use the outputs shown in the catalogue (the correction factor for this system would be equal to 1).

For a system with “Delta T” other than 50°C, calculating the new output for the radiator is simple:

  • In 'Correction factor table', find the actual delta T for your system and the corresponding correction factor
  • Multiply the output in the catalogue by the correction factor

Example calculation

Radiator output in the AEL catalogue (based on delta T=50°C) = 194W
Your system's delta T = 35°C
From the table, correction factor = 0.629
Therefore, the output of your radiator = 194W * 0.629 = 122W


After you have worked out the heat requirement for your room (AEL's easy-to-use BTU calculator will help you do this), how can you check that the radiator you have chosen will provide enough heat output?

There is a simple calculation to check if the radiator will provide sufficient heat output. You must check the “delta T”.

What is the "delta T"?

In the AEL radiator catalogue, a heat output figure is provided for each of the radiators, along with the radiator's dimensions. The heat output figure is reported for a specific "delta T". The delta T is the difference between a target room temperature and the average temperature of water in the radiator. The average temperature of the radiator depends on the temperature of the water entering and leaving the radiator, which may be different in your heating system.

delta T = (Room temperature) - (Average radiator water temperature)

If the delta T of your system is different from the one shown in the catalogue, then you will need to calculate a new heat output. This is easily done by multiplying the output figure in the catalogue by a correction factor.

Correction factor table

Delta T (°C) Correction factor
5 0.050
10 0.123
15 0.209
20 0.304
25 0.406
30 0.515
35 0.629
40 0.748
45 0.872
50 1.000
55 1.132
60 1.267
65 1.406
70 1.549
75 1.694

The diagram below illustrates a case where the desired room temperature is 20°C and the average water temperature across the radiator is 70°C. The difference, the "Delta T", is 50°C.

 

 

If the “Delta T” in the catalogue is 50°C, it is perfect to just use the outputs shown in the catalogue (the correction factor for this system would be equal to 1).

For a system with “Delta T” other than 50°C, calculating the new output for the radiator is simple:

  • In 'Correction factor table', find the actual delta T for your system and the corresponding correction factor
  • Multiply the output in the catalogue by the correction factor

Example calculation

Radiator output in the AEL catalogue (based on delta T=50°C) = 194W
Your system's delta T = 35°C
From the table, correction factor = 0.629
Therefore, the output of your radiator = 194W * 0.629 = 122W


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AEL Heating Solutions Ltd
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Runcorn
WA7 1TQ
Tel: 01928 579068
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How to calculate the "delta T" for a radiator