Different companies sometimes state different heat outputs for the same radiators, why?

Calculating your heat output requirement from a radiator and finding the appropriate size of radiator can be confusing. 

For example:

You provide your room measurements and your radiator specialist, Joe Bloggs Radiators, recommends that you need 1200 Watts heat output from your radiator.  Consequently they recommend a radiator that meets your requirements; X radiator in white, 600mm high x 1000mm wide, which gives out 1264 Watts. 

However, your plumber tells you that the same radiator, X radiator in white, 600mm high x 1000mm wide but from his supplier, ACME Radiators, only gives out 1000 Watts.  How can this be? 

The answer is probably that Joe Bloggs Radiators are advertising their heat outputs at the British standard whereas ACME Radiators are advertising their heat outputs using the newer European standard. 

To explain, heat outputs can be measured in 2 different ways; the way they are measured is done against the “delta T” or “Δt” of the system. 

In the UK, the standard for calculating heat outputs is illustrated by the following example:

• Flow water temperature (on entering the radiator) – assumed to be at 90˚C
• Return water temperature (on exiting the radiator) – assumed to be at 70˚C
• This means the average water temperature running through the system is assumed to be   80 ˚C
• From this figure, you minus the average room temperature – assumed to be 20 ˚C
• This equates to the Δt60 ˚C standard.

In Europe, the standard for calculating heat outputs is illustrated by the following example:

• Flow water temperature (on entering the radiator) – assumed to be at 75˚C
• Return water temperature (on exiting the radiator) – assumed to be at 65˚C
• This means the average water temperature running through the system is assumed to be   70 ˚C
• From this figure, you minus the average room temperature – assumed to be 20 ˚C
• This equates to the Δt50 ˚C standard.

To be clear, there is no difference in the radiator, it is just a different way of recording the performance and heat output.  Like metric versus imperial; the numbers may be different, but they mean the same thing. 

The reason that retailers still often use the original British Δt60 ˚C is because most domestic plumbers and heating engineers still calculate heat requirements to this standard.  Although most manufacturers now using the European standard of Δt50 ˚C.

The important thing is to compare like with like.  Check whether your heat output requirement has been calculated at the Δt60 ˚C or Δt50 ˚C standard then match the radiator output using the same standard.

It is easy to convert a Δt50 ˚C heat output to a Δt60 ˚C heat output and vice versa:

• To convert Δt50 ˚C to Δt60 ˚C, multiply Δt50 ˚C heat output by 1.264.
• To convert Δt60 ˚C to Δt50 ˚C, divide Δt60 ˚C heat output by 1.264.

So in conclusion, when buying a radiator, make sure you are comparing like with like; check the testing standards used and convert the figures as necessary or, to save yourself time and hassle, contact a reputable radiator expert who can do all this for you.

For more information on radiator heat outputs and expert advice on choosing a radiator with the appropriate heat output for your space then contact a radiator specialist such as Feature Radiators.  For face-to-face advice and to see over 250 display models then visit their showroom at The Old Post Office, 134-140 Main Street, Bingley, West Yorkshire, BD16 2HL, call them on 01274 567789 or browse their products at www.featureradiators.co.uk.