Heat loss & gain calculator.
Estimate a room’s steady-state winter heat loss and summer sensible gains. See the fabric, outdoor-air and internal contributions separately.
Know what
the result includes.
A transparent early estimate
Fabric heat transfer = Σ(U × area) × temperature difference. Outdoor-air heat transfer = 0.33 × air changes per hour × room volume × temperature difference. Summer sensible gain adds the entered solar, people, equipment and lighting gains. Winter heat loss does not subtract internal gains.
This is a simplified steady-state room estimate. It does not calculate latent loads, dynamic solar response, thermal mass, thermal bridges, ground heat transfer, heat recovery, diversity or warm-up allowances. Summer gains are not a complete cooling-load calculation. Do not use it alone to select heating or cooling equipment.
Use project design temperatures and verified U-values. A full room-by-room assessment remains necessary: see CIBSE’s heating and heat-pump factsheets. The outdoor-air coefficient is also explained in the UK heat-network tool’s methodology.
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