Room-by-Room Heat Loss Calculator

Under MCS standards (MIS 3005-D) and BS EN 12831, a room-by-room heat loss survey is mandatory for heat pump installations. Because heat pumps operate at lower flow temperatures (e.g. 45°C–50°C), each individual room's radiator must be precisely sized to that room's specific thermal loss. Sizing the whole system from a rough whole-house estimate leads to freezing bedrooms, boiling bathrooms, or inefficient boiler cycling.

When a living room is heated to 21°C and an adjacent unheated hallway or spare bedroom is at 16°C, heat flows through the internal partition wall (driven by the 5°C internal ΔT). BS EN 12831 accounts for this inter-room transmission to ensure emitters in warmer rooms can maintain their comfort setpoint even when surrounding doors are open.

Yes. Our Room-by-Room Engine includes an instant 'Export Schedule (CSV)' feature that downloads a complete tabulated schedule with room dimensions, floor areas, volumes, heat losses, and recommended radiator capacities ready for spreadsheet analysis or contractor handover.

For intermittently heated buildings where heating is turned off overnight, BS EN 12831 specifies a reheat capacity allowance (f_rh) between 10 to 25 W/m² depending on building mass and pre-heating duration. For continuously modulated heat pump systems running with weather compensation, reheat margins are kept minimal (0%–10%) to prevent over-sizing.

Hallways typically do not have dedicated external envelope walls on upper floors, but they experience high ventilation air changes due to front doors opening and stairwell stack effect. Assign hallways an 18°C setpoint and allocate their ventilation load to ensure the central heating radiator is adequately sized.

If a single radiator is undersized, the entire heating system must run at a higher flow temperature to keep that one cold room warm. This raises return water temperatures across all radiators, preventing condensing boilers from condensing and significantly reducing heat pump SCOP efficiency.