Can a heat loss calculation be completed without a site visit?

Sometimes. A desktop heat loss calculation can be prepared from clear plans and known property data, but the result depends on the quality of the drawings, room dimensions, fabric assumptions and installer review.

What information is needed for a desktop heat loss calculation?

Useful inputs include plans, room names, dimensions, ceiling heights, wall and roof construction, insulation evidence, glazing details, emitter context and any known limitations or assumptions.

When should installers book a site survey instead?

A site survey is usually better when drawings are missing, dimensions are uncertain, property fabric is unclear, access constraints matter or the installer needs photos and site evidence for the wider job file.

Heat loss

Desktop heat loss calculation from plans

Remote heat-loss support for installer teams when drawings and property evidence are strong enough to work from.

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Required inputs

What helps a remote calculation

Desktop heat loss is useful when a site visit is not practical or when the installer already has reliable drawings. It should still be treated as an evidence-led process, not a guess from a floor area.

Plan data

Room and fabric details

Floor plans, room-by-room dimensions, windows, wall construction, and insulation context.

System context

Existing system inputs

Current heating system details to align the calculation with realistic replacement assumptions.

Assumption log

Called out uncertainty

Any unknown is recorded clearly so design and cost review can reference it before commitment.

Limits

When desktop heat loss is not enough

Drawings are missing, out of date or do not show room-by-room measurements clearly.
Construction details, insulation levels or glazing assumptions are unknown.
The installer needs photos for MCS, BUS, design review or customer handover.
There are access, emitter, cylinder, plant-space or electrical questions that cannot be checked remotely.

In those cases, a measured heat loss survey or wider heat pump survey gives the design team a stronger file.

Report output

What the report should make clear

Which inputs came from plans, installer notes or supplied property evidence.
Which assumptions were used for fabric, glazing, room areas and ceiling heights.
Where a site survey or installer confirmation is still needed before final design.
How the heat-loss output links to emitter review, ASHP sizing and the wider job file.

Vertex keeps those assumptions visible so the office, design and installation teams are not working from a number with no context. For live scope and pricing, use installer pricing.

If the job later moves to a measured survey, the desktop work still helps because the team already knows which details need checking on site. That makes the visit more focused and gives the final heat-loss file a clearer audit trail.