A survey is most useful when it tests a clear brief. Gather bills, measurements and household patterns before the installer arrives, then ask for the design assumptions in writing.
Before the visit
- twelve months of electricity and heating bills
- current tariff rates and cheap periods
- half-hourly data where available
- number and timing of showers and baths
- cylinder, boiler and controls photographs
- consumer unit and meter-area photographs
- cupboard dimensions and access route
- known water-pressure or heating problems
For whole-home heating
Request a room-by-room heat-loss calculation. List room temperatures, working patterns, planned extensions and insulation work that may change the design.
Questions during the survey
Ask what the unit supplies, how it charges, how long it lasts on the design day and what happens when depleted. Confirm electrical work, pipe changes, controls, structural support and service clearance.
Evidence to leave with
The proposal should identify the exact model, design demand, charge schedule, predicted annual input, excluded work, certification route and source for important performance figures.
Red flags
Be cautious when a model is selected before demand is discussed, the survey ignores tariff times, or savings are offered without your existing consumption.
Your next step
Send the same brief to at least three installers. A common input makes differences in scope, assumptions and price much easier to see.
Sources
Primary and independent references checked by our editorial team.
- Installing renewable technology at home — Energy Saving Trust Checked 10 Nov 2026
- Before you get work done on your home — Citizens Advice Checked 10 Nov 2026