Choosing an air source heat pump installer

MCS certification is not optional

The Microgeneration Certification Scheme certifies installers of small-scale renewable technology. It matters for one blunt reason: without an MCS-certified installer you cannot claim the grant. Not "it is harder", not "you need extra paperwork". You cannot claim it at all, in England, Wales or Scotland.

MCS certification also means the installation is carried out to a defined standard, that the noise assessment for permitted development is done properly, and that there is a complaints route through the certification body if things go wrong. An installer who is "working towards" MCS or who "uses an MCS umbrella" is worth a very careful look, because the certificate has to be in the name of the company doing your job.

Four questions that tell you everything

Ask every installer these, and compare the answers rather than the prices.

1. What design flow temperature is this quoted at?

The single most revealing question. A good installer answers immediately with a number, usually between 40 and 50°C, and explains what it means for your radiators. A poor one will not know, or will say it does not matter. It matters more than anything else in the quote.

2. Can I see the room-by-room heat loss calculation?

MCS requires one. If they cannot produce it, the unit has been sized by guesswork, and an oversized unit cycles inefficiently while an undersized one leaves you cold. Both are expensive mistakes.

3. Which radiators are you changing, and which are you leaving?

You want a specific list, room by room. "We'll see when we get there" means the price will change once your old boiler is already in a skip.

4. Who commissions it, and how long do they spend?

Commissioning, and specifically setting the weather compensation curve, is where good systems are separated from bad ones. If the answer is "we turn it on and go", expect to run at a high flow temperature forever.

Warning signs

• A quote without a site visit. Nobody can size a heat pump from a phone call or a web form. Walk away.
• No mention of radiators at all. Either they have done a careful calculation showing none need changing, which is rare, or they have not looked.
• Pressure to sign today. Grant funding is not about to run out this afternoon.
• Vagueness about MCS. Ask for the certificate number and check it on the MCS website. It takes two minutes.
• A quote that is dramatically cheaper. Look for what has been excluded rather than assuming you found a bargain.
• "You won't need a cylinder." An air-to-water heat pump cannot make instant hot water. If you are on a combi you need a cylinder. Full stop.

What a good quote contains

• Room-by-room heat loss calculation with the design flow temperature stated
• Specific heat pump make, model and output
• Cylinder size and location
• A named list of radiators being changed and their sizes
• The noise assessment position and result
• Gross price, grant amount and the net figure you actually pay
• Estimated annual running cost at the design flow temperature
• Warranty terms and what annual servicing costs

If a quote is missing more than one or two of these, it is not really a quote. It is a number.