Heat loss inputs: measurements and assumptions

If a calculation can’t be explained, it can’t be trusted. The pack should make inputs and assumptions visible.

1) What we measure (scope-led)

Heat loss work is always to the agreed scope. But in practical terms, reliable inputs usually come down to the same few building blocks.

• Room geometry: lengths/widths/heights where needed for the agreed output.
• Openings: windows/doors that materially affect heat loss (type and rough size/quantity).
• Construction notes: anything that changes the assumption set (age bands, extensions, visible insulation cues).
• Constraints: inaccessible areas, unknown build-ups, unusual ceiling heights, partial rooms.

2) Room-by-room checklist (installer-friendly)

If you want room-by-room outputs, the survey pack should make these inputs easy to verify:

• Room name and basic function (bedroom, living, kitchen, hall).
• Dimensions captured consistently (so the next person can follow).
• External walls vs internal walls (what is actually exposed).
• Openings: count and type (double glazed, patio door, etc.).
• Notable quirks: bay windows, vaulted ceilings, conservatory links, large glazing.

3) Assumptions (make them visible)

Assumptions aren’t “bad” — hidden assumptions are. A good pack documents assumptions in plain language so installers can explain them to homeowners.

• What we know (measured/observed) vs what we assume (unknown build-up, inaccessible loft).
• Why we assumed it (age, visible construction, previous works, typical build patterns).
• What would change it (e.g. insulation confirmation, access to a void).

4) Evidence photos (useful, not excessive)

• Wide shot of the room for context → close-up of key construction details
• Any visible insulation cues, unusual build details, or constraints
• Loft hatch / plant spaces if relevant to your scope

5) Handoff: what makes it “installer-ready”

• Consistent section order (so teams can train once)
• Constraints summarised early (not buried in notes)
• Notes placed next to the evidence (where possible)
• Clear enough to explain to a homeowner without re-writing

Disclaimer: This guide is general best-practice for evidence-led inputs. Always follow your scheme/provider requirements and project-specific scope.