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When buying a radiator, you might see ratings like T60, T50 or T30 next to the heat output. This is the "Delta Rating."
It sounds technical, but it's actually quite simple: it tells you how much heat a radiator will produce based on your boiler's water temperature.
Understanding this ensures you don't buy a radiator that leaves your room cold!
We always list T60, T50 and T30 heat outputs on our product page tech spec for your reference.
The Simple Definition
Delta T (ΔT) is simply the difference between the temperature of the water inside the radiator and the room temperature you want to achieve.
Imagine you want your living room to be 20°C.
Your boiler sends water to the radiator at 75°C and it leaves at 65°C (an average of 70°C).
70°C (Average Water Temp) minus 20°C (Room Temp) = 50°C difference.
This is ΔT50 (Delta T 50), which is the standard rating for most modern UK gas boilers.
You don't need a thermometer to make a safe guess. Use these simple rules of thumb to find your rating:
The "Touch Test":
- Too hot to touch: ΔT60
- If it's hot but you can hold your hand on it for a second: ΔT50
- If it feels warm like a bath: ΔT30
Not all heating systems run at the same temperature. If you have a different system, the radiator won't get as hot, so it won't give out the full heat output listed on the box.
| Heating System | Standard Rating | Water Temp |
|---|---|---|
| Older Boilers (Non-condensing) | ΔT60 | Very Hot (~80°C) |
| Modern Gas Boilers | ΔT50 | Hot (~70°C) |
| Heat Pumps (Air/Ground source) | ΔT30 | Warm (~45°C) |
If you have a Heat Pump (Low Temperature / ΔT30) system, standard steel radiators need to be much larger to heat your room properly.
Aluminium radiators are the perfect solution because:
Most retailers (including us) display heat outputs at ΔT50 because that is the UK standard for modern homes.
If you are unsure: Assume you need ΔT50.
If you have a Heat Pump: You need significantly larger radiators. Look for the ΔT30 rating, or multiply the required BTU by roughly 2.5 to get a big enough radiator.
The radiator will still work and fit on the wall perfectly fine. However, it might not get hot enough to warm your room fully. For example, a ΔT60 radiator on a ΔT50 system will be underpowered. You might need to turn your boiler temperature up, which costs more money.
No. Physically, the metal box is exactly the same. The rating is just a calculation of performance. A "1000 BTU" radiator at ΔT50 is exactly the same object as a "1260 BTU" radiator at ΔT60.
As a rough rule of thumb, to convert a ΔT60 rating to ΔT50, divide the BTU by 1.26. To go the other way (ΔT50 to ΔT60), multiply by 1.26.
