HTHOMETALLYTHE PRACTICAL HOME GUIDE

Heating/ CALCULATOR

Radiator output at lower water temperature

Estimate how a radiator’s published heat output changes at a different supply, return and room temperature.

Use the manufacturer output at the stated rated temperature difference.
Often ΔT50 for EN 442 radiator data; verify the product sheet.
Water temperature entering the radiator at the condition being checked.
Water temperature leaving the radiator at the same condition.
Use the intended indoor design temperature.
Use the manufacturer value when available; 1.3 is a common screening value for panel radiators.
Count only radiators with the same published output and operating condition.
Mean water temperature

40.0 °C

Actual mean-water-to-room difference

20.0 °C

Estimated output per radiator

456 W

Estimated total output

2,279 W

Output retained versus rated condition

30.4 %

Interpretation:This operating condition provides about 455.79 W per radiator and 2,278.97 W in total—30.39% of the published rated-condition output. Compare it with the room-by-room design heat loss.

Arithmetic mean water temperature, steady operation and the entered radiator exponent. Published rated output must use the entered rated temperature difference. Flow limits, uneven temperatures, enclosure, paint, air pockets, valve authority, pipe loss, intermittent control and manufacturer-specific corrections are excluded. Use product data and a room-by-room design for final selection.

FROM ESTIMATE TO ACTION

Use the result, not just the number.

01

Verify the inputs

Measure or document each input. If a value is only an estimate, record its source and test a conservative alternative.

02

Keep the calculation traceable

Save the input link or copied result together with the date, units and assumptions. A number without its inputs cannot be checked later.

03

Confirm the decision

Compare the estimate with the related guide, current product data and requirements that apply at your location before buying or building.

Inputs to verify

Published output per radiator (W)
Use the manufacturer output at the stated rated temperature difference.
Rated temperature difference (°C)
Often ΔT50 for EN 442 radiator data; verify the product sheet.
Design supply temperature (°C)
Water temperature entering the radiator at the condition being checked.
Design return temperature (°C)
Water temperature leaving the radiator at the same condition.
Room temperature (°C)
Use the intended indoor design temperature.
Emitter exponent (n)
Use the manufacturer value when available; 1.3 is a common screening value for panel radiators.
Matching radiators (radiators)
Count only radiators with the same published output and operating condition.

Continue your calculation

Heating

Hydronic heating flow rate

Convert a heating load and design supply-return temperature difference into a water-flow estimate.