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Delta T 50° and Delta T 60° - What's the Difference?
29 Oct

Delta T 50° and Delta T 60° - What's the Difference?

Posted By: Gordon Mowat Times Read: 18849 Comments: 0

Delta T, also written Δt, represents the difference between two temperatures - e.g. between a radiator and a room, and is used as a means of stating a room's heating requirement, and radiator output.

Most radiator sellers show radiator output in terms of Δt50°. This is because Δt50° is the current European testing standard for modern boilers such as condensation boilers which have lower flow and return temperatures than older boiler systems which use ΔT 60°.

So, in order to avoid radiators being incorrectly sized, it is important to know the heating system's temperatures and take them into consideration. It is also extremely important when calculating your rooms' requirements to know what basis you are using - for example, if your calculation is based on ΔT 50° and you choose radiators whose output is based on ΔT 60°, then the output of your radiators will be too low.

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°.  This is a typical scenario.

So, when comparing radiator outputs and prices be sure to check which ΔT is being quoted. You can use the following table to compare radiator outputs:

ΔT at 60°C Conversion Factor ΔT at 50°C Conversion Factor
60° 1.000 60° 1.280
55° 0.901 55° 1.154
50° 0.781 50° 1.000
45° 0.699 45° 0.895
40° 0.599 40° 0.767
35° 0.513 35° 0.657
30° 0.424 30° 0.543
25° 0.338 25° 0.433
20° 0.256 20° 0.328
15° 0.179 15° 0.229

Example: Let's assume we have a radiator that gives 2000 Watts at ΔT (delta T) = 60°. At ΔT (delta T) = 40°, the output would be 2000 x 0.599 (from the table above) = 1198 Watts, At ΔT (delta T) = 20°, the output would be just (2000 x 0.256) = 512 Watts.

NB:  Some sites quote radiators at Δt at 70°C, which is extremely unrealistic as it means the inlet water temperature is in the region of 95°C, which is nearly boiling! 

The reason to use Δt at 70°C is for "marketing purposes". (In other words, to make a particular manufacturer's radiators look to have a far better output than others .... )

The conversion factor from Δt at 70°C to Δt at 50°C is 0.6455.
Example:  a radiator which has a stated output of 11000 BTUs Δt 70°C has an output of only 7100 BTUs at Δt at 50°C. So if you actually need 11000 BTUs from this radiator it is highly unlikely that the radiator will achieve it!


So - please MAKE SURE you are clear about how a room's heating requirement is calculated AND how radiator output is shown on any supplier's website, and feel free to call us if you need any assistance.

All radiators on our website are shown at Δt 50°C to help ensure that any radiator we supply will be Fit for Purpose.


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