All Radiators Max Power Output Calculator

Use the radiator calculator to work out the power in watts for each radiator, then enter each power output in the total power calculator below. This tool is most useful for combi boilers.

0 W

0.00 kW

How to calculate and adjust the power level

How many radiators are there?

Flow temperature 80°C

20°C 90°C

Return temperature 60°C

0°C 90°C

Flow-to-Return Difference (ΔT) 20°

0° 20°

Room temperature 20°C

0°C 30°C

Mean water temperature 70°C

Radiator Delta T 50

Choose Radiator Panel Type

Connection

×0.91

×0.95

×1

Enter: Height cm

Enter: Length cm

Enter Height (cm)

60 cm

Enter Length (cm)

100 cm

0 W

Total max power load

Name each room and enter its wattage, or add the figure from the calculator above.

0 W

0.00 kW

Formula

Watts = (ΔT / 50)^1.3 × Panel factor × Connection factor × (Height cm × 10) × (Length cm × 10)
ΔT = mean water temperature − room temperature

ΔT: Mean water temperature minus room temperature. Mean water temperature is the average of the flow and return temperatures.
(ΔT / 50)^1.3: Temperature correction. This equals 1 when ΔT is 50.
Panel factor: Panel no Convector (10) 0.001292, Single (11) 0.0017, P+ (21) 0.0023, Double (22) 0.0032, Triple (33) 0.0045. Type 10 is 76% of Single (11).
Connection factor: BBOE ×0.91, TBSE ×0.95, TBOE ×1.
Height cm × 10: Height converted from centimetres to millimetres.
Length cm × 10: Length converted from centimetres to millimetres.

Important: Output is approximate at the selected Delta T. The default is 50°C. Panel no Convector (10) is assumed at 76% of Single (11). Use the kW total for boiler range rating. Always confirm the figure with a qualified heating engineer.