Radiator ΔT is the difference between the average water temperature and the room temperature. The same rail usually delivers less heat at ΔT30 than at ΔT50.
Work out the temperature difference
Add flow and return temperatures, divide by two, then subtract the design room temperature. Flow at 75 °C, return at 65 °C and a room at 20 °C gives ΔT50. Flow at 55 °C, return at 45 °C and the same room temperature gives ΔT30.
Use the output for the exact model
Look for a published rating at your operating ΔT or use the manufacturer’s correction data. As a worked example, if the model’s ΔT30 factor is 0.51, an 800 W ΔT50 rating becomes about 408 W at ΔT30. Use the factor for the rail you are considering.
Compare output with the room requirement
If the bathroom needs 500 W at its design temperature, the example rail is about 92 W short. Check another model among our wide towel radiators or discuss a second heat source. For lower-temperature systems, see the heat pump towel radiator guide.
Frequently asked questions
Does a 50 °C flow temperature mean ΔT50?
Average the flow and return temperatures first, then subtract the room temperature. A 50 °C flow alone cannot establish ΔT.
See the bathroom heating and BTU guide for the full process from room heat loss to choosing a rail.