Questions to ask before you sign

You are not trying to catch anybody out. A good installer will answer all of these easily and will be glad you asked, because it means the rest of the conversation can be a real one.

What you are listening for is whether the answer is specific, because specificity comes from work already done.

About the design

"Can I see the room-by-room heat loss calculation?"

Heat pumps. A good answer hands it over, or says when it will exist. A bad answer explains why a house like yours does not need one, and the standard makes no such exception.

"What flow temperature is this designed for?"

Heat pumps. A good answer is a number: "45 degrees." A bad answer is "low temperature", or a look of mild surprise.

"Which room needs the hottest water, and what would it cost to change that radiator?"

Heat pumps. This is the question that separates people who have done the design from people who have priced a box. The whole house runs at whatever temperature its worst room demands, so one undersized radiator sets your bill. A good answer names the room. A very good answer has already priced the alternative.

"What five numbers did you use for the generation estimate?"

Solar. Capacity, postcode, pitch, direction, shading. A good answer lists them. A bad answer says it comes from their software.

"Did somebody go and assess the shading, and what did they find?"

Solar. A good answer describes what was found, including the chimney. A bad answer is "there's no shading" from somebody who has seen a satellite photograph.

About the numbers

"Is that saving figure based on what I generate, or what I use myself?"

Solar. These differ by a factor of three or four. A good answer distinguishes them without hesitating, and knows roughly what proportion you would use. A bad answer treats them as the same thing.

"What are you assuming I pay for electricity and gas?"

Every saving figure rests on two prices. A good answer states them and will happily redo the sum with yours, and a bad answer cannot say what they are.

"What does this heat pump deliver on the coldest day, at the flow temperature you have designed for?"

Heat pumps. Not the headline rating. A unit sold as 8 kW can be 5.5 kW at the conditions that matter. A good answer knows the difference and has the figure, and a bad answer repeats the headline number.

About the job

"What is not included in this price?"

An open question, deliberately. A good answer volunteers the awkward ones: scaffolding, an electrical supply upgrade, making good, taking the old system away. A bad answer is "everything's included", which is never quite true.

"What happens if you find something unexpected once you start?"

Something usually is found. A good answer describes how it would be raised with you and priced before it is done. A bad answer is that it never happens.

"Who stands behind the workmanship if you are no longer trading?"

A good answer names the insurance-backed guarantee provider and offers the policy. A bad answer is a reassurance about how long they have been in business, which is not the same thing and does not survive an insolvency.

What you are listening for

Across all eleven, the pattern is the same. Somebody who has surveyed your house and designed a system can answer in specifics without reaching for anything. Somebody who has looked up a house of roughly your size in a table will answer in generalities and move the conversation towards the price.

Two other things worth noticing while you are there.

Did they tell you anything you did not want to hear? Almost every house has something: a radiator that needs changing, a shaded corner of the roof, a supply that needs upgrading. Somebody who found nothing at all either did not look, or is not telling you.

Did they ask to see your bills? A year of your own consumption is the best information available about your house. An installer who does not ask for it is quoting on estimates.

After the appointment

Do not decide in the room. Consumer law gives you a cooling-off period on a contract agreed at home, and any pressure to sign before you have read it is a reason to slow down, not speed up.

Get the answers in writing. "Yes, the flow temperature is 45" said in your kitchen is not the same as a design document, and it is the document that gets installed.