Most homeowners getting heat pump quotes receive a system size recommendation with very little explanation of how it was arrived at. A number appears on a proposal (8 kW, 12 kW, 14 kW) and it is presented as fact. What rarely gets explained is whether anyone actually calculated it properly.
Heat loss calculation is not complicated in principle. It requires someone to measure the property, account for its fabric, apply design temperatures and arrive at a figure in kilowatts that represents how much heat the building loses on the coldest day of the year. That figure then determines what size heat pump is needed.
The problem, as anyone who has spent time on the Renewable Heating Hub forums will know, is that a significant proportion of installers either skip this step entirely or treat it as a box-ticking exercise rather than a genuine engineering decision. The result is systems that are oversized, underperforming or both.
This tool is not a full heat loss calculator. A proper room-by-room calculation is what you need before any heat pump is specified. What this is, is a sense checker… a fast way to interrogate the figure you’ve been given and spot the ones that simply don’t add up.
It draws on two independent sizing cross-checks (the watts per square metre approach used by experienced installers to sense-check design figures against property age and fabric, and a gas consumption cross-reference that uses your historical energy use as a proxy for actual heat demand) alongside a set of installer qualification questions drawn from recurring failure patterns seen in the community.
If the number on your quote survives all three checks, that’s reassuring. If it doesn’t, you now have the language to push back, and a reason to ask for the full heat loss calculation before you sign anything.
A few important caveats. The W/m² bands used in this tool are rules of thumb developed by experienced practitioners, not precise engineering values. Unusual properties (very high ceilings, extensive glazing, solid walls with no insulation or significant unheated volumes) can sit legitimately outside the expected ranges. The tool flags, it does not decide! What it decides is whether the conversation with your installer needs to go further.
If you want to discuss your figures or get a second opinion the Renewable Heating Hub forums are the place to bring them.
This tool is in beta. The logic is based on established rules of thumb used by experienced heat pump practitioners, but the building categories and thresholds are still being refined. Results should be treated as a starting point for conversation, not a definitive verdict. If you spot something that doesn’t look right for your property or installation, please tell us in the forums… your feedback is actively shaping the next version.
Heat Pump Installation Sense Checker
Two things go wrong most often with heat pump installations: incorrect sizing and poor commissioning. This tool checks both. It is not a substitute for a full room-by-room heat loss calculation — but it will tell you quickly whether the numbers and the planned approach deserve more scrutiny.
Built by Renewable Heating Hub
