What a good quote looks like

Most quotations are a page of equipment and a price at the bottom. That is not enough to decide on, and it is not enough to compare against another one.

What you want is a quotation that shows how it reached its numbers. Not so you can check the arithmetic line by line, but because a company that can show its working has done the work, and one that cannot has guessed.

Whatever you are buying

A price that says what is included. The usual omissions are scaffolding, making good afterwards, electrical upgrades, taking the old system away, and anything discovered once the work starts. A cheap quote that leaves those out becomes the expensive one in March.

The actual equipment, by make and model. Not "a 6 kW air source heat pump" or "premium panels". A model number, so you can look it up.

Three separate warranties, named separately. The manufacturer's warranty on the kit. The installer's warranty on the work. And an insurance-backed guarantee, which is the one that stands behind the second if the company stops trading. People routinely assume they have the third without ever seeing the policy, so ask for its number.

What happens if something goes wrong. A complaints procedure, and who to escalate to above the company itself.

Deposit and cancellation terms. Deposits are normal, but a deposit approaching half the job is not, and any deposit should be protected.

If you are buying a heat pump

Three things matter more than everything else on the page.

A room-by-room heat loss calculation

Not a total. A table with a row for every room, showing how much heat each one loses on a cold day. This is the foundation the whole design rests on, and you are entitled to see it.

Why it matters: it decides the size of the heat pump and the size of each radiator. A machine sized by rule of thumb, or by the size of the boiler it is replacing, is very often far too big. An oversized heat pump cannot turn down enough on a mild day, so it runs in short bursts all winter, wears itself out and costs more than it should. You will not notice — the house will be warm — you will just be paying for it.

If a quotation arrives with no heat loss calculation, ask for it. If it does not exist, that is the answer to your question.

The design flow temperature

A specific number, in degrees. Not "low temperature". This is the temperature of the water going round your radiators, and it governs your bill for the next twenty years.

A quotation that does not state it has left out the most consequential decision in the design. And if it does state a high one, ask what it would take to bring it down — usually a couple of larger radiators, which is a few hundred pounds against a saving that repeats every year.

A room-by-room schedule of radiators

Which radiators are being kept, which replaced, and what each delivers in the room it serves at the design flow temperature.

This is where you find out whether the flow temperature above is real or aspirational. A design at 45 degrees with every existing radiator kept is very likely to be a design at 55 degrees that has not admitted it yet.

Also worth having: the heat pump's output at your conditions, not its headline rating. A unit sold as 8 kW usually means 8 kW on a mild day making lukewarm water. On a cold day making the water you actually need, it might be 5.5. It is that figure that has to cover your house.

If you are buying solar

The five numbers behind the generation estimate. How many kilowatts of panels, your postcode, the pitch of the roof, the direction it faces, and the shading allowance. With those five, anybody can reproduce the annual figure, so a quote that gives only the answer cannot be checked.

The shading allowance in particular. If the quote assumes no shading at all and you have a chimney, somebody has not been to look.

Self-consumption, stated separately from generation. These are two very different numbers and they get quietly swapped. Generation is what the panels make. Self-consumption is how much of it you use instead of selling, and it is the one that determines the saving. A quote that shows you the annual generation multiplied by the price you pay for electricity is overstating the benefit by a factor of three or four.

The layout. Which panels are on which inverter input, and whether optimisers are fitted. On a roof with any shading this matters more than the brand of panel.

Confirmation the roof has been checked by somebody competent to check it.

What the gaps usually mean

A savings figure with no assumptions attached. Savings depend on fuel prices, on how you run the house, and on the design. A number with none of that attached cannot be checked, which is generally why it is presented that way.

A discount that expires today. Nothing about the cost of installing a heat pump changes between Tuesday and Thursday.

"You had a 24 kW boiler so you need a 15 kW heat pump." That is not a calculation, and boilers are almost always oversized too. It is the reasoning the room-by-room method exists to replace.

Reluctance to hand over the calculations. They exist, or they should. A company unwilling to show you is telling you something useful.

Using it

Before you read the prices, read the numbers. Put the same figures into the heat pump or solar calculator and see whether the quotation lands anywhere near.

It will not match exactly, and it does not need to. What you are looking for is whether it is in the same territory. A quoted heat pump three times the size of your own estimate is a question worth asking, and the answer will tell you a great deal about whoever wrote it.