Why do we show outputs as Delta 60 (Δt 60ºC), Delta 50 (Δt 50ºC) and Delta 30 (Δt 30ºC) for cast iron radiators?

thermometer for warm cast iron radiators The output of our Cast Iron radiator’s can be expressed in BTUs or watts.

The wattage is based on the system’s likely operating temperature or the correlation between the flow temperature in the system, the return temperature and an average room temperature and is either shown as Delta 60 (Δt 60ºC) or Delta 50 (Δt 50ºC) or Delta 30 (Δt 30ºC), i.e. 90/70/20 (delta T60) or 80/60/20 (delta T50).

Delta 60 (Δt 60ºC) is the British Rating System whilst the newer European Rating is Delta 50 (Δt 50ºC ). Delta 30 (Δt 30ºC) is reserved largely for systems that run off of ground source heat pumps or geothermal heat sources. Delta 30 measures are popular for our customers in Scandinavia, Iceland and Canada.

Most UK plumbers and heating engineers may still calculate heat requirements using the original British Delta 60 rating. However, the industry standard as defined by the British Cast Iron Radiators Association is to use Delta 50 Calculations. To comply with this and to avoid confusion, our heat outputs are shown in both.

  • To convert Delta 50 to Delta 60 multiply Delta 50 heat output by 1.264
  • To convert Delta 60 to Delta 50 divide Delta 60 heat output by 1.264

The heat outputs of your chosen cast iron radiators are unlikely to be exactly the same as your heat requirement. Therefore, it is generally better to slightly oversize your cast iron radiators.

If you have any questions on this or any other issues about our products, please do not hesitate to contact us on 01723 321000.