Understand and convert Delta T radiator outputs
Delta T Conversion
B2-EN442 states all hydronic radiator and towel rail outputs are tested and presented at Delta T 50° / ΔT 50° as standard. To calculate the output at a different Delta T, complete the form below and select your required Delta T conversion.
Delta T correction-factor tables
Hydronic radiator outputs are normally compared at ΔT50. Lower-temperature systems produce less heat from the same radiator, while higher Delta T systems produce more. These rounded reference values support quick comparisons for modern boilers, heat pumps and older high-temperature systems.
Outputs quoted at ΔT50
Multiply output quoted at ΔT50 by the factor shown.
| Required Delta T | Correction factor |
|---|---|
| ΔT5 | 0.05 |
| ΔT10 | 0.12 |
| ΔT15 | 0.21 |
| ΔT20 | 0.3 |
| ΔT25 | 0.41 |
| ΔT30 | 0.51 |
| ΔT35 | 0.63 |
| ΔT40 | 0.75 |
| ΔT45 | 0.87 |
| ΔT50 | 1 |
| ΔT55 | 1.13 |
| ΔT60 | 1.27 |
| ΔT65 | 1.41 |
| ΔT70 | 1.55 |
| ΔT75 | 1.69 |
Outputs quoted at ΔT60
Multiply output quoted at ΔT60 by the factor shown.
| Required Delta T | Correction factor |
|---|---|
| ΔT15 | 0.185 |
| ΔT20 | 0.262 |
| ΔT25 | 0.344 |
| ΔT30 | 0.43 |
| ΔT35 | 0.519 |
| ΔT40 | 0.605 |
| ΔT45 | 0.705 |
| ΔT50 | 0.787 |
| ΔT55 | 0.906 |
| ΔT60 | 1 |
Worked examples
A radiator producing 1,000 Watts at ΔT50 produces 750 Watts at ΔT40: 1,000 × 0.75.
An output quoted as 1,000 Watts at ΔT60 converts to 787 Watts at ΔT50: 1,000 × 0.787.
Use manufacturer-certified output data where available. A heating professional should confirm radiator sizing and system temperatures.