Heating Load & Radiator Sizing Calculator (Watts & Sections per m²)

Calculate room heating power in Watts and the number of radiator sections needed based on floor area, climate zone and water ΔT (EN 442).

Room Floor Area (m²)

Ceiling Height (Meters)

Winter Climate Zone

Water Supply ΔT (EN 442)

Required Heating Power1.863 W

Radiator Sections Needed15 sections

Thermal Output (kcal/h)1.602 kcal/h

Specific Heat Load103.5 W/m²

Radiator Thermal Output & Delta-T (ΔT) Correction Formula (EN 442)

Thermal Standard (EN 442 & ASHRAE): Radiator heat output drops non-linearly with lower water temperatures according to the exponent n ≈ 1.30.

ΔT = ((T_supply + T_return) / 2) - T_room
Actual Heat Output: P = P_rated(ΔT50) × (ΔT / 50) ^ 1.3

Climate Zone	Reference Climate Type	Well Insulated Home	Average / Older Insulation
Zona A / B	Mild Coastal / Mediterranean Climate	65 W/m²	80 W/m²
Zona C	Temperate Maritime / Oceanic Climate	75 W/m²	95 W/m²
Zona D	Cold Continental / Inland Plateau	90 W/m²	110 W/m²
Zona E	Severe Mountain / High Altitude (>800m)	105 W/m²	130 W/m²

Depending on insulation and climate zone, rooms require 65 to 110 W/m². At standard boiler ΔT 50°C, a 60cm aluminum radiator section outputs ~125 W.

Under EN 442, heat output scales with (ΔT / 50)^1.3. Running a low-temperature heat pump at ΔT 30°C reduces radiator output by roughly 48%.