Radiator sizing for ASHP projects: start with survey quality
Most radiator sizing problems are not maths problems. They are input quality problems.
Inputs that move the result
- Reliable room dimensions and external wall context.
- Window and door assumptions that are visible and reviewable.
- Emitter condition notes where replacements are likely.
- Clear exceptions and inaccessible areas flagged in the report.
Typical causes of rework
- Incomplete room data hidden in long note sections.
- Assumptions not documented next to evidence photos.
- No single source of truth for updated survey files.
How to make the report easier to use
Use one clear report format, deliver it through the portal, and keep assumptions explicit. That is the fastest route to fewer redesigns and cleaner install planning.
What the survey should make obvious
Radiator sizing depends on the heat loss result, flow temperature assumptions, emitter condition, and whether the room data is complete enough to trust. A strong survey does not try to hide the uncertain parts. It shows where dimensions, insulation evidence, glazing assumptions, and emitter notes came from so the designer can decide quickly whether the existing radiator is likely to stay, be upsized, or need a different conversation with the customer.
- Room dimensions and ceiling heights recorded consistently.
- Existing emitter type, size, and location captured where visible.
- External wall, glazing, and insulation assumptions kept reviewable.
- Rooms with missing or uncertain evidence flagged before design sign-off.
Where installers lose time
The common delay is not that the final radiator schedule is difficult to calculate. It is that the office team has to ask what was actually measured, whether the photos support the assumptions, or whether a room was missed. That creates a loop between surveyor, designer, installer, and homeowner. The report should reduce that loop by making the evidence usable without another site conversation.
- Bedrooms, extensions, and open-plan spaces need clear room boundaries.
- Older radiators need notes where size, type, or condition is uncertain.
- Rooms with poor access should say exactly what could not be checked.
- Heat loss assumptions should point back to the site evidence, not sit in isolation.