What’s different, what each is used for, and what evidence helps.
Installers and homeowners often mix these up. Here’s a clear, practical explanation and where to start if you want fast delivery with minimal follow‑ups.
Use the EPC evidence checklist if you want the practical survey-day document list.
Exact requirements depend on scope — we confirm what you need before booking.
A heat loss calculation is used to support heat pump sizing, radiator or emitter review, and room-by-room design decisions. It depends heavily on measurements, fabric assumptions, room temperatures, ventilation assumptions, and whether the survey evidence is good enough to defend the result.
An EPC is a separate energy performance certificate route. It can still matter for grant, compliance, or customer decisions, but it is not a substitute for a detailed room-by-room heat loss calculation when the installer needs sizing evidence.
For retrofit heat pump work, the practical answer is often both: EPC evidence for the certificate or grant context, and heat loss evidence for design confidence. The survey should make clear which output is being ordered and why.