A heat pump install is a five-figure decision. The grant funding helps, but you’re still committing to a piece of kit that will sit outside your house for fifteen to twenty years, and the difference between a good install and a bad one is almost entirely down to the company that fits it.
The technology itself is mature. The industry around it, less so. A lot of installers entered the market in the last three years to chase grant money, and the quality range is wide.
Here are seven questions to ask every installer before you sign. If they fumble any of them, walk away.
1. What’s your sizing methodology?
This is the single most important question. An undersized heat pump won’t keep up on cold days. An oversized one will short-cycle, which wears out the compressor faster and runs less efficiently.
The right answer is a room-by-room heat loss calculation, done in line with MCS 3005 (the relevant standard). This means the installer measures every external wall, window, and door, factors in your local design temperature, and works out the kilowatt demand for each room.
If they say “we’ll size it off your old boiler” or “we usually fit a 12kW for a house this size”, that’s the wrong answer. Boiler sizing has almost nothing to do with heat pump sizing, because boilers are usually massively oversized to begin with.
Ask to see the heat loss survey document before you accept the quote. A real one runs to several pages.
2. Are you MCS accredited?
The Microgeneration Certification Scheme is the quality mark for renewable heat installers in the UK. If your installer isn’t MCS-accredited, you cannot claim the Boiler Upgrade Scheme grant. End of story.
But there’s a deeper reason to insist on it. MCS sets minimum standards for design, installation, and aftercare. A company without MCS has no oversight, no audit trail, and no protection for you if something goes wrong.
Verify their membership yourself by searching their company name on the MCS public register. Don’t trust a logo on a leaflet.
While you’re at it, check they’re also signed up to TrustMark, the government-endorsed quality scheme for tradespeople. The Boiler Upgrade Scheme requires both.
If you haven’t worked out whether you’d qualify for the grant yet, run a heat pump grant self-assessment first. It saves a wasted visit.
3. What warranty terms are on offer, and who honours them?
Ask three things:
- Product warranty (how long the manufacturer covers the unit itself, usually five to seven years)
- Workmanship warranty (how long the installer covers their own fitting work)
- What happens if the installer goes bust (this is where MCS and TrustMark insurance-backed guarantees kick in)
The product warranty is meaningless if the installer disappears and no one is left to honour callouts. A solid installer will offer at least two years on workmanship, and the MCS framework provides an additional layer through the consumer code (HIES, RECC, or similar) they’re signed up to.
Get the warranty terms in writing as part of the quote, not as a verbal reassurance.
4. What’s the noise rating, and where will the unit sit?
Heat pumps make noise. Modern units are quiet, but they’re not silent, and where the installer puts the outdoor unit affects how much that noise reaches your neighbours.
Ask for:
- The sound power level (measured in decibels at 1 metre, usually 45 to 55 dB for a domestic unit)
- The proposed location, with a sketch or photo
- Confirmation it sits at least 1 metre from any neighbour’s habitable room window, or whatever your local council requires under the permitted development rules
If the unit will sit close to a fence shared with a neighbour, the right move is to mention it to them before install rather than after. A good installer will help with the wording.
5. Does my install need planning permission?
Most heat pump installs fall under permitted development, which means no formal planning application is needed. But “most” isn’t “all”. You need planning permission if:
- The unit would be installed on a flat roof or a wall facing the highway
- Your property is listed
- You’re in a conservation area, national park, or area of outstanding natural beauty
- The outdoor unit is bigger than 0.6 cubic metres in volume
A reputable installer will check all of this before quoting and tell you whether you need to apply. Permitted development rules also change occasionally, so the installer’s knowledge needs to be current.
If your installer shrugs at this question, that’s a flag. Planning enforcement after a non-compliant install is expensive and slow to resolve.
6. Does my electrical supply have enough capacity?
A heat pump pulls more electrical current than a gas boiler. Most modern UK homes have an 80-amp or 100-amp main fuse, which is fine, but older properties sometimes still have 60-amp supplies that need upgrading first.
Ask the installer:
- Will you carry out an electrical load assessment before install?
- If my main fuse needs upgrading, who arranges it (the installer or me with the DNO)?
- Will my consumer unit need replacing?
A main fuse upgrade is usually free if requested through your Distribution Network Operator, but it can take a few weeks to schedule. A consumer unit replacement is a separate job, typically £400 to £800, and a good installer will tell you up front if your existing one isn’t compatible.
7. What does post-install commissioning look like?
Commissioning is the bit where the installer sets up the heat pump to actually run efficiently in your specific home. Done properly, it takes hours. Done badly, it gets skipped and your running costs are 20 to 30 percent higher than they should be.
A proper commissioning includes:
- Setting the weather compensation curve so flow temperature adjusts to outdoor conditions
- Balancing the radiators so every room heats evenly
- Configuring the hot water schedule and any Legionella cycle
- Showing you how to use the controls
- A first-year service visit included in the quote
Ask for a written commissioning certificate at handover. MCS-accredited installers should provide one as standard.
A practical next step
Once you’ve got two or three quotes back and you’ve put each installer through these seven questions, you’ll have a clear winner. The right installer answers without flinching. The wrong one starts hedging.
If grant funding is part of the picture, double-check your eligibility through a free checker, and browse the wider grants landscape so you know what else might apply to your home.
For an operator perspective on home-energy infrastructure, the lessons from running your own systems apply surprisingly well to picking installers too.
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