Sizing estimate
Estimated peak heat loss
8.6 kW
Recommended heat pump size range
9-10 kW
Hot water allowance
1.5 kW
Total recommended system range
10.5-11.5 kW
Important caveat
This is an estimate. A formal MCS heat loss calculation is needed before installation.
| System type | Typical sizing approach | Indicative size |
|---|---|---|
| Gas boiler | Can be oversized for hot water recovery without immediate comfort issues | 12-15 kW |
| Heat pump | Closer to design heat loss, with steady low-temperature output | 9-10 kW |
| Direct electric | Usually sized close to peak loss, often room by room | 9-11 kW |
Design note
Methodology
Simplified heat loss model
The estimator uses UK rule-of-thumb heat loss intensities derived from floor area and envelope quality. Insulation level anchors the core watts-per-kelvin-per-square-metre assumption: roughly 3W/K/m² for poor homes, 2W/K/m² for average, 1.3W/K/m² for good, and 0.8W/K/m² for excellent-performing homes.
Build age, glazing, property type, storeys, and region then shift the result up or down to reflect likely fabric quality, exposed surface area, and colder external design conditions. The final peak heat loss is converted to kW and expanded into a sensible size band.
Hot water allowance is handled separately because domestic hot water demand depends more on occupancy than on the building fabric. Heat pump sizing is kept close to estimated peak heat loss, while gas boilers are shown with a slightly larger range because boiler outputs are often selected more generously.
This is a planning tool only. Installer design should still include room-by-room heat loss, emitter sizing, hot water cylinder specification, pipework checks, and defrost / weather-compensation strategy before any equipment is ordered.