You will see three different numbers on the way through, and they mean different things.
The instant estimate
Worked out from your energy certificate and the handful of questions you answered. It takes seconds and it is genuinely useful — it tells you the rough size of system a home like yours needs, and roughly what that costs — but it is built on assumptions about your walls, windows and glazing rather than on anybody having looked.
It is a range, and it is deliberately shown as one.
The surveyed design
After a full survey, the calculation is redone from measured rooms: real window sizes, real orientations, real construction, room by room. This is a much better number, and it is what the quote is based on.
The quote
Your installer’s price for doing the work. It comes from them, not from us, and it accounts for things a calculation cannot know — scaffolding, a difficult pipe run, how busy they are in March.
What none of these are
None of it is a compliance certificate. Our calculations are indicative design: they are good enough to size a system, plan it and price it, and they are not the certified paperwork required for a grant-funded installation. Your installer produces that, and your installer owns the final design.
We say so on every screen and in every document that carries a figure, and it is not legal throat-clearing — it is the actual division of responsibility. We do the arithmetic; a qualified person signs off the design.