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Understanding your heating output: A guide to Delta T radiator specs

Choosing the right radiator for your home can be a daunting task, especially when it comes to understanding how much heat it can output. To help make things easier, we've put together this guide to Delta T radiator specs, which can help you calculate the heat output you need for any given area in your home.


What is Delta T?

Delta T is a figure that is based on the temperature difference between the water circulating throughout the central heating system in comparison with the ambient room temperature. The formula for Delta T is:

Average Temperature of Water in Radiators – Average Preferred Ambient Temperature = Delta T 

  • It's important to note that when you're looking at radiators online, you should be looking at a Delta T 50º output as standard.
  • The older British Rating System uses Delta 60 (Δt 60ºC), while the newer European Rating System uses Delta 50 (Δt 50ºC).
  • While many radiator shops and radiator brochures still sell radiators based on Delta 60 outputs, this assumes that the water entering the radiator is around 85⁰C, which is not the case with modern condensing boilers that supply water at lower temperatures.
  • For this reason, all of the radiator outputs listed on The Radiator Shop are listed with a minimum output value of Delta T 50.

How to convert Delta T50 to Delta T60 and Delta T60 to Delta T50?

It varies by radiator manufacturer but in general you can use the following rough estimate:

  • To convert Delta T 50 output of a radiator to Delta T 60, multiply the Delta T 50 heat output by 1.264.
  • To convert Delta T 60 output of a radiator to Delta T 50, divide the Delta T 60 heat output by 1.264.


What Delta T do I use for low temperature systems?

  • If you're installing a low-temperature system like a heat pump, you'll need to adjust the Delta T for your radiators.
  • Since the temperature of the water will be much lower with a heat pump, you'll still want the same room temperatures, which means your Delta T will be lower.
  • In general, you need to find out what heat the radiator will give out at a Delta T 30 or Delta T 25.
  • If you need to know the output of a radiator on The Radiator Shop's site at these temperatures, you can send an email to

A Final Note

Remember that the heat outputs of your chosen radiators are unlikely to be exactly the same as your heat requirement. So, always go for a radiator size with a slightly higher output than you require for the room and fit thermostatic radiator valves to control the room temperature.

PS: You can calculate your heat requirement using our free BTU Calculator.

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