House heat loss

through the envelope (U×A×ΔT) → required boiler power

Structures

Walls

Walls, m²

Windows, m²

U windows

Roof/ceiling, m²

U roof

Floor, m²

U floor

ΔT, K

Infiltration, %

ΔT = indoor minus design outdoor temp (+22 − (−20) = 42 K for central Ukraine).

Result

Total heat loss

9,20 kW

boiler with 15% margin: ≥ 11,00 kW

Walls3 150,00 W

Windows1 176,00 W

Roof/ceiling1 260,00 W

Floor2 100,00 W

Infiltration1 537,00 W

Q = A × U × ΔT for each structure + infiltration. This is peak demand in frost; seasonal use will be 2–3× lower. An oversized boiler short-cycles and wears out — take the nearest standard rating above the calculation, not 'double for safety'.

About House heat loss

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