Radiator sizing result
Required room heat output
1,320 W
Required emitter output at chosen flow temp
2,245 W
Existing radiator at chosen flow temp
1,098 W
Verdict
Undersized
Suggested upgrade path
Correction factor table
| Flow temp | Approx. output vs Δ50 rating | Example 1,800W radiator |
|---|
Methodology
How the room heat and radiator correction are estimated
Room heat demand is estimated from floor area, ceiling height, insulation quality, number of external walls, and room type. The calculator uses a simplified watts-per-square-metre base, then adjusts upward for colder target temperatures, bathrooms and living rooms, taller ceilings, and more exposed wall area.
Lower flow temperatures reduce radiator output because the average water temperature sits closer to room temperature. Manufacturer catalogues normally quote radiator output at Δ50, which corresponds roughly to a standard 75/65/20 test condition.
To translate that Δ50 rating into lower temperature operation, this tool applies typical correction factors used in radiator sizing guides: around 0.30 at 35°C flow, 0.55 at 45°C flow, 0.78 at 55°C flow, and 1.0 at 65°C+ standard conditions. Exact outputs vary by radiator type, panel depth, and mean water temperature.
Treat the result as an early screening check. Final emitter sizing should be confirmed room by room from manufacturer data using the intended flow and return temperatures.