Installation
Heat Pump Hot Water Cylinder UK: What Size Do You Need?
Heat pumps cannot work with a combi boiler setup — they need a hot water cylinder. Here's how to choose…
October 9, 2026
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Once you have three quotes, comparing them on price alone is a mistake if they’re specifying different equipment and scope. Use this framework:
The heat pump market has grown rapidly, and with it the number of installers who have the paperwork but not the expertise. These are the warning signs that should make you look elsewhere:
- A quote without a site visit. It is physically impossible to design a heat pump system correctly without visiting the property and measuring room-by-room. Online quote tools that give you an instant fixed price based on your postcode and house type are sales funnels, not engineering proposals.
- No mention of heat loss calculation. If a quote arrives and there’s no reference to a heat loss calculation or design flow temperature, the installer has not done the fundamental design work. Ask explicitly: “Can you show me the heat loss calculation this is based on?” A good installer will answer confidently and provide documentation.
- Very low price with no radiator upgrades. Almost all homes coming from a gas boiler running at 70–80°C will need at least some radiator work to run efficiently at 45°C. An installer who prices a system with no radiator changes in a full house of standard radiators either hasn’t done the heat loss properly, or is planning to run the system at a high flow temperature (which costs you money in running costs for the life of the system).
- Pressure to sign quickly or “before the grant runs out.” The BUS grant is available; it doesn’t run out at a moment’s notice. Installers who use urgency tactics are trying to prevent you from getting comparison quotes.
- No specific heat pump references or reviews. A five-star plumbing and boiler business is not necessarily a five-star heat pump business. Ask how many ASHPs the company has installed in the past 12 months and ask to speak to a recent customer. Good installers are happy to provide references.
How to compare quotes meaningfully
Once you have three quotes, comparing them on price alone is a mistake if they’re specifying different equipment and scope. Use this framework:
- Compare design flow temperatures first. The quote designed to run at 40–45°C will cost more today but save you hundreds of pounds every year in electricity. The quote designed to run at 55°C looks cheaper but will underperform.
- Check whether cylinder replacement is included and whether the specified cylinder is an indirect (heat pump-compatible) model with an adequate primary coil surface area. A cheap or undersized cylinder is a common corner-cutting move.
- Check heat pump unit sizing. If two quotes specify a 6 kW unit and one specifies a 10 kW unit for the same house, ask the outlier to explain why. Oversized units short-cycle and lose efficiency; the 6 kW quotes may well be right, or the 10 kW installer may have identified something the others missed.
- Check what’s excluded. Some quotes exclude commissioning, electrical certification, or disposal of the old boiler. These costs add up — make sure you’re comparing apples with apples.
For a full cost breakdown and what’s included in typical installation costs, see our heat pump costs guide for 2026.
National installers vs local specialists: which is better?
There’s no universal answer. Large national companies (British Gas Heat Pumps, OVO Heat Pumps, EON Heat Pumps, Octopus Energy Services) offer standardised processes, clear consumer protection, and the backing of a major organisation if problems arise. They also tend to be competitive on price because of purchasing power. The downside is that you may get less flexibility in system design and a less personalised relationship.
Smaller independent specialists — particularly those with Heat Geek accreditation or who have built a specific reputation for ASHP work in your area — often deliver better technical quality because their business reputation depends entirely on each installation going well. The Heat Pump Association’s installer finder is a useful resource for finding reputable specialists.
The right answer is: get quotes from both types and let the quality of the quotation documentation tell you what you need to know. The installer who does the best job of explaining their design process is usually the installer who will do the best job of installing your system. For everything you need to know about grant eligibility, see our BUS grant guide — and for an honest overall assessment, is a heat pump worth it for your home?
The Microgeneration Certification Scheme (MCS) is the industry standard for heat pump installations in the UK. MCS certification for an installer means they have been assessed against installation standards (MIS 3005 for ASHPs), carry appropriate insurance, use certified products, and follow a quality process that includes heat loss calculations, proper commissioning, and documentation.
MCS certification is not optional if you want the £7,500 Boiler Upgrade Scheme grant — Ofgem requires the installation to be carried out by an MCS-certified installer. But certification matters beyond the grant: the MCS Consumer Code gives you access to an independent dispute resolution process if something goes wrong, and requires the installer to provide a minimum 2-year Workmanship Warranty. This is the basic consumer protection floor for heat pump installations.
You can verify any installer’s MCS certification directly at mcscertified.com/find-an-installer. Do not rely on a company’s word for this — take 30 seconds and check it. Certification can expire or be suspended, so check it specifically, not just whether the company claims to be certified.
Where to find heat pump installers in the UK
The best starting points for finding installers are:
- MCS Installer Finder (mcscertified.com): the official directory, searchable by postcode and technology type. This is the authoritative source — every installer listed here has current MCS certification.
- Heat Geek’s installer finder (heatgeek.com): Heat Geek is a training and quality standard organisation focused specifically on heat pumps. Their registered installers have passed additional training and genuinely specialise in heat pump design — not just certified boiler engineers who’ve done a heat pump course.
- Manufacturer-recommended installers: major brands like Vaillant (Advance Installer programme), Mitsubishi (Diamond Dealer), Nibe, and Daikin maintain networks of trained and preferred installers. These aren’t guarantees of quality, but they do indicate relevant training on that specific product.
- Comparison platforms: services like Heatable, Checkatrade, and Rated People can surface local MCS-certified installers quickly, though you should always independently verify MCS status and reviews.
Word of mouth from a neighbour who recently had a heat pump installed is also highly valuable — especially if you can see the system running and ask about their experience with the installer directly.
What a good heat pump quote looks like
A professional heat pump quote should be detailed and itemised. You should be able to see exactly what you’re getting for the price. Here is what a good quote includes — and what it tells you about the installer’s competence:
| What should be in the quote | Why it matters |
|---|---|
| Heat pump make, model, and kW output | Tells you the unit is sized to the heat loss calculation — not a round number |
| Design flow temperature (e.g. 45°C at design conditions) | Lower is better for efficiency; anything above 55°C suggests undersizing or poor insulation assessment |
| Hot water cylinder make, model, and litres | Cylinder sizing should match household hot water demand — not one-size-fits-all |
| Itemised list of radiators to be replaced or added | Shows the installer has identified which emitters are undersized at the design flow temperature |
| Electrical work scope (new circuit, any consumer unit work) | Electrical work must be Part P-compliant; confirm it is included |
| MCS Workmanship Warranty duration | Minimum 2 years required under MCS Consumer Code |
| Commissioning included explicitly | Commissioning is where systems are tuned properly — it shouldn’t be an afterthought |
| BUS grant applied by installer (£7,500 deducted) | You should see the grant deducted on the quote, not receive a gross price and claim separately |
For full context on the installation process from survey to switch-on, see our heat pump installation guide.
Red flags: when to walk away
The heat pump market has grown rapidly, and with it the number of installers who have the paperwork but not the expertise. These are the warning signs that should make you look elsewhere:
- A quote without a site visit. It is physically impossible to design a heat pump system correctly without visiting the property and measuring room-by-room. Online quote tools that give you an instant fixed price based on your postcode and house type are sales funnels, not engineering proposals.
- No mention of heat loss calculation. If a quote arrives and there’s no reference to a heat loss calculation or design flow temperature, the installer has not done the fundamental design work. Ask explicitly: “Can you show me the heat loss calculation this is based on?” A good installer will answer confidently and provide documentation.
- Very low price with no radiator upgrades. Almost all homes coming from a gas boiler running at 70–80°C will need at least some radiator work to run efficiently at 45°C. An installer who prices a system with no radiator changes in a full house of standard radiators either hasn’t done the heat loss properly, or is planning to run the system at a high flow temperature (which costs you money in running costs for the life of the system).
- Pressure to sign quickly or “before the grant runs out.” The BUS grant is available; it doesn’t run out at a moment’s notice. Installers who use urgency tactics are trying to prevent you from getting comparison quotes.
- No specific heat pump references or reviews. A five-star plumbing and boiler business is not necessarily a five-star heat pump business. Ask how many ASHPs the company has installed in the past 12 months and ask to speak to a recent customer. Good installers are happy to provide references.
How to compare quotes meaningfully
Once you have three quotes, comparing them on price alone is a mistake if they’re specifying different equipment and scope. Use this framework:
- Compare design flow temperatures first. The quote designed to run at 40–45°C will cost more today but save you hundreds of pounds every year in electricity. The quote designed to run at 55°C looks cheaper but will underperform.
- Check whether cylinder replacement is included and whether the specified cylinder is an indirect (heat pump-compatible) model with an adequate primary coil surface area. A cheap or undersized cylinder is a common corner-cutting move.
- Check heat pump unit sizing. If two quotes specify a 6 kW unit and one specifies a 10 kW unit for the same house, ask the outlier to explain why. Oversized units short-cycle and lose efficiency; the 6 kW quotes may well be right, or the 10 kW installer may have identified something the others missed.
- Check what’s excluded. Some quotes exclude commissioning, electrical certification, or disposal of the old boiler. These costs add up — make sure you’re comparing apples with apples.
For a full cost breakdown and what’s included in typical installation costs, see our heat pump costs guide for 2026.
National installers vs local specialists: which is better?
There’s no universal answer. Large national companies (British Gas Heat Pumps, OVO Heat Pumps, EON Heat Pumps, Octopus Energy Services) offer standardised processes, clear consumer protection, and the backing of a major organisation if problems arise. They also tend to be competitive on price because of purchasing power. The downside is that you may get less flexibility in system design and a less personalised relationship.
Smaller independent specialists — particularly those with Heat Geek accreditation or who have built a specific reputation for ASHP work in your area — often deliver better technical quality because their business reputation depends entirely on each installation going well. The Heat Pump Association’s installer finder is a useful resource for finding reputable specialists.
The right answer is: get quotes from both types and let the quality of the quotation documentation tell you what you need to know. The installer who does the best job of explaining their design process is usually the installer who will do the best job of installing your system. For everything you need to know about grant eligibility, see our BUS grant guide — and for an honest overall assessment, is a heat pump worth it for your home?
The single biggest factor in whether a heat pump works well is not the brand — it’s the quality of the installation. A poorly designed system from a reputable brand will underperform and leave you frustrated; a well-designed system from a second-tier manufacturer, commissioned by an experienced engineer who ran proper heat loss calculations, will deliver exactly what was promised. Finding the right installer is therefore the most important decision in the whole process — and it’s one where cutting corners costs you for the next fifteen years.
This article contains affiliate links. If you buy through them, we may earn a small commission at no extra cost to you. This doesn’t affect our editorial independence — we only recommend products we’d genuinely suggest to a friend.
Key Takeaways
- MCS certification is mandatory — required for the BUS grant and for the consumer protection framework
- Always get at least three quotes; don’t accept the first one without comparison
- Any installer who quotes without visiting and running a heat loss calculation should be rejected immediately
- Good quotes are detailed and itemised; vague lump-sum quotes are a warning sign
- Check reviews specifically for heat pump work — an installer’s Gas Safe reputation doesn’t guarantee ASHP competence
Why MCS certification is the non-negotiable starting point
The Microgeneration Certification Scheme (MCS) is the industry standard for heat pump installations in the UK. MCS certification for an installer means they have been assessed against installation standards (MIS 3005 for ASHPs), carry appropriate insurance, use certified products, and follow a quality process that includes heat loss calculations, proper commissioning, and documentation.
MCS certification is not optional if you want the £7,500 Boiler Upgrade Scheme grant — Ofgem requires the installation to be carried out by an MCS-certified installer. But certification matters beyond the grant: the MCS Consumer Code gives you access to an independent dispute resolution process if something goes wrong, and requires the installer to provide a minimum 2-year Workmanship Warranty. This is the basic consumer protection floor for heat pump installations.
You can verify any installer’s MCS certification directly at mcscertified.com/find-an-installer. Do not rely on a company’s word for this — take 30 seconds and check it. Certification can expire or be suspended, so check it specifically, not just whether the company claims to be certified.
Where to find heat pump installers in the UK
The best starting points for finding installers are:
- MCS Installer Finder (mcscertified.com): the official directory, searchable by postcode and technology type. This is the authoritative source — every installer listed here has current MCS certification.
- Heat Geek’s installer finder (heatgeek.com): Heat Geek is a training and quality standard organisation focused specifically on heat pumps. Their registered installers have passed additional training and genuinely specialise in heat pump design — not just certified boiler engineers who’ve done a heat pump course.
- Manufacturer-recommended installers: major brands like Vaillant (Advance Installer programme), Mitsubishi (Diamond Dealer), Nibe, and Daikin maintain networks of trained and preferred installers. These aren’t guarantees of quality, but they do indicate relevant training on that specific product.
- Comparison platforms: services like Heatable, Checkatrade, and Rated People can surface local MCS-certified installers quickly, though you should always independently verify MCS status and reviews.
Word of mouth from a neighbour who recently had a heat pump installed is also highly valuable — especially if you can see the system running and ask about their experience with the installer directly.
What a good heat pump quote looks like
A professional heat pump quote should be detailed and itemised. You should be able to see exactly what you’re getting for the price. Here is what a good quote includes — and what it tells you about the installer’s competence:
| What should be in the quote | Why it matters |
|---|---|
| Heat pump make, model, and kW output | Tells you the unit is sized to the heat loss calculation — not a round number |
| Design flow temperature (e.g. 45°C at design conditions) | Lower is better for efficiency; anything above 55°C suggests undersizing or poor insulation assessment |
| Hot water cylinder make, model, and litres | Cylinder sizing should match household hot water demand — not one-size-fits-all |
| Itemised list of radiators to be replaced or added | Shows the installer has identified which emitters are undersized at the design flow temperature |
| Electrical work scope (new circuit, any consumer unit work) | Electrical work must be Part P-compliant; confirm it is included |
| MCS Workmanship Warranty duration | Minimum 2 years required under MCS Consumer Code |
| Commissioning included explicitly | Commissioning is where systems are tuned properly — it shouldn’t be an afterthought |
| BUS grant applied by installer (£7,500 deducted) | You should see the grant deducted on the quote, not receive a gross price and claim separately |
For full context on the installation process from survey to switch-on, see our heat pump installation guide.
Red flags: when to walk away
The heat pump market has grown rapidly, and with it the number of installers who have the paperwork but not the expertise. These are the warning signs that should make you look elsewhere:
- A quote without a site visit. It is physically impossible to design a heat pump system correctly without visiting the property and measuring room-by-room. Online quote tools that give you an instant fixed price based on your postcode and house type are sales funnels, not engineering proposals.
- No mention of heat loss calculation. If a quote arrives and there’s no reference to a heat loss calculation or design flow temperature, the installer has not done the fundamental design work. Ask explicitly: “Can you show me the heat loss calculation this is based on?” A good installer will answer confidently and provide documentation.
- Very low price with no radiator upgrades. Almost all homes coming from a gas boiler running at 70–80°C will need at least some radiator work to run efficiently at 45°C. An installer who prices a system with no radiator changes in a full house of standard radiators either hasn’t done the heat loss properly, or is planning to run the system at a high flow temperature (which costs you money in running costs for the life of the system).
- Pressure to sign quickly or “before the grant runs out.” The BUS grant is available; it doesn’t run out at a moment’s notice. Installers who use urgency tactics are trying to prevent you from getting comparison quotes.
- No specific heat pump references or reviews. A five-star plumbing and boiler business is not necessarily a five-star heat pump business. Ask how many ASHPs the company has installed in the past 12 months and ask to speak to a recent customer. Good installers are happy to provide references.
How to compare quotes meaningfully
Once you have three quotes, comparing them on price alone is a mistake if they’re specifying different equipment and scope. Use this framework:
- Compare design flow temperatures first. The quote designed to run at 40–45°C will cost more today but save you hundreds of pounds every year in electricity. The quote designed to run at 55°C looks cheaper but will underperform.
- Check whether cylinder replacement is included and whether the specified cylinder is an indirect (heat pump-compatible) model with an adequate primary coil surface area. A cheap or undersized cylinder is a common corner-cutting move.
- Check heat pump unit sizing. If two quotes specify a 6 kW unit and one specifies a 10 kW unit for the same house, ask the outlier to explain why. Oversized units short-cycle and lose efficiency; the 6 kW quotes may well be right, or the 10 kW installer may have identified something the others missed.
- Check what’s excluded. Some quotes exclude commissioning, electrical certification, or disposal of the old boiler. These costs add up — make sure you’re comparing apples with apples.
For a full cost breakdown and what’s included in typical installation costs, see our heat pump costs guide for 2026.
National installers vs local specialists: which is better?
There’s no universal answer. Large national companies (British Gas Heat Pumps, OVO Heat Pumps, EON Heat Pumps, Octopus Energy Services) offer standardised processes, clear consumer protection, and the backing of a major organisation if problems arise. They also tend to be competitive on price because of purchasing power. The downside is that you may get less flexibility in system design and a less personalised relationship.
Smaller independent specialists — particularly those with Heat Geek accreditation or who have built a specific reputation for ASHP work in your area — often deliver better technical quality because their business reputation depends entirely on each installation going well. The Heat Pump Association’s installer finder is a useful resource for finding reputable specialists.
The right answer is: get quotes from both types and let the quality of the quotation documentation tell you what you need to know. The installer who does the best job of explaining their design process is usually the installer who will do the best job of installing your system. For everything you need to know about grant eligibility, see our BUS grant guide — and for an honest overall assessment, is a heat pump worth it for your home?
#boiler-upgrade-scheme
#heat-pump-installation
#heat-pump-installers
#heat-pump-quotes
#mcs-certified
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