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Heat Loss Calculations
Room-by-room BS EN 12831 calculations with the fabric and ventilation basis shown in full.
Heat Loss Calculations
Heat loss is the number every other decision depends on, and it is the one most often produced by a rule of thumb. Watts per square metre gets you a plausible boiler size and an indefensible underfloor design, because it tells you nothing about the room with three external walls and a large glazed opening.
We calculate room by room to BS EN 12831 — fabric transmission through each element with its own U-value, thermal bridging, ventilation and infiltration on the appropriate basis, and intermittent-heating reheat allowance where the operating pattern justifies it. Every input is visible in the output, so your engineer or a building control officer can follow the arithmetic rather than take it on trust.
These calculations stand on their own for boiler and heat pump sizing, radiator scheduling, MCS documentation and compliance submissions — not only as an input to an underfloor design.
What you receive
Every item below is issued in your own template, with your layer conventions, title block and revision scheme.
- Room-by-room heat loss schedule in watts and W/m²
- Element-by-element fabric breakdown with U-value source stated
- Ventilation and infiltration losses with the assumed basis
- Thermal bridging allowance and its derivation
- Whole-building design heat load and diversified plant load
- Emitter or floor output requirement per room
- Sensitivity note on the assumptions that most affect the result
- Calculation appendix suitable for submission or audit
Production detail
| Typical turnaround | 24 hours per dwelling, 3–5 days commercial |
|---|---|
| Standards | BS EN 12831, BS EN ISO 6946, CIBSE Guide A, MCS requirements |
| Design conditions | CIBSE / national external design temperatures by location |
| Deliverable formats | XLSX with visible formulae, PDF appendix |
| U-value handling | Calculated from build-up or taken from your specification |
| Revisions | Two rounds included |
Software and formats
We work in your toolchain. If something you use is not listed, ask — the list below is only what we use most.
Frequently asked
Send one heat loss calculations job and see how we work
Scope, price and programme come back in writing before anything starts. Most first projects are a single deliverable so you can judge us on output, not on a pitch.