What it costs
Real installed prices for 2026, before and after grant, and the six things that actually move the number on your property.
CostsWhy a cylinder is unavoidable, what it means if you are on a combi, how much space to find and what the hot water actually performs like.
Tell us about your property and an MCS-certified engineer will be in touch, usually the same working day.
Yes. An air-to-water heat pump needs a hot water cylinder, and there is no way around it.
The reason is output. A combi boiler produces something like 30kW on demand, which is what lets it heat water instantly as it flows through. A domestic heat pump produces perhaps 8kW, and produces it most efficiently when running steadily. It cannot deliver instant hot water at a usable flow rate. Instead it heats a cylinder gradually and you draw from the store.
The only exception is an air-to-air heat pump, which heats and cools air and does not touch your hot water at all. If you go that route you keep your existing hot water arrangement entirely.
Then you need to find space for a cylinder, and this is one of the bigger practical obstacles to heat pump retrofit in the UK, because millions of homes had their cylinders ripped out when combis were installed.
Common locations, in rough order of preference:
A typical family cylinder holds 180 to 250 litres and is roughly 55 to 60cm in diameter and 1.5 to 1.8m tall, plus clearance for pipework and the immersion. Sizing follows occupancy:
| Household | Typical cylinder |
|---|---|
| 1–2 people | 150 – 180 litres |
| 3–4 people | 180 – 210 litres |
| 5+ people | 250 – 300 litres |
Heat pump cylinders are not interchangeable with boiler cylinders. They need a much larger internal coil surface area, because they are being fed water at 50°C rather than 75°C. Reusing an old cylinder is a false economy that will leave you short of hot water.
Yes, with one behavioural difference. A cylinder at 48 to 50°C delivers water at a perfectly normal temperature for showering and washing, at excellent flow rate, better than many combis manage. What changes is that the store is finite. Run three long baths back to back and you will empty it, and reheating takes an hour or two rather than being instant.
In practice most households never notice, because the cylinder reheats between uses and can be scheduled to be full when you need it.
Because a heat pump stores water at a lower temperature than a boiler would, systems include a periodic pasteurisation cycle that raises the cylinder to around 60°C, typically weekly, using the immersion heater or the heat pump itself. This is automatic and built into the controls. It uses a small amount of extra energy and it is not optional.
If you have solar PV, hot water is where it pays best with a heat pump. Scheduling the cylinder reheat for the middle of the day means you are frequently heating water on generation you would otherwise export cheaply. It is one of the simplest running cost improvements available.
Air-to-water heat pumps do, always. They cannot produce instant hot water at usable flow rates the way a 30kW combi can, so they heat a cylinder gradually and you draw from the store. Air-to-air heat pumps are the exception, as they do not provide hot water at all.
You need to find space for one. The original airing cupboard, loft, garage, utility or under the stairs are the usual answers, and slimline or horizontal cylinders exist for properties where nothing standard fits. It is one of the more common practical obstacles to retrofit.
Roughly 150 to 180 litres for one or two people, 180 to 210 for three or four, and 250 to 300 for five or more. Physically that is around 55 to 60cm across and 1.5 to 1.8m tall, plus clearance.
Usually not. Heat pump cylinders need a much larger internal coil because they are fed at around 50°C rather than 75°C. An old boiler cylinder will reheat slowly and leave you short of hot water.
Yes. A cylinder at 48 to 50°C is perfectly normal for showering and washing, often at better flow rates than a combi. The difference is that the store is finite, so several baths in a row will empty it and reheating takes an hour or two.
Systems run an automatic periodic pasteurisation cycle, typically weekly, raising the cylinder to around 60°C using the immersion or the heat pump. It is built into the controls and is not optional.
Real installed prices for 2026, before and after grant, and the six things that actually move the number on your property.
CostsThe Boiler Upgrade Scheme in England and Wales, Home Energy Scotland north of the border, and what applies in Northern Ireland.
GrantsSurvey, design, grant, installation and commissioning, with honest timescales and a clear account of the disruption.
ProcessWhy sizing comes from a room-by-room heat loss calculation and never from floor area or your old boiler's output.
SizingWhich radiators need upsizing at a lower flow temperature, and why this is the single biggest swing factor in your quote.
RadiatorsWhy heat pumps need a cylinder, what happens if you are on a combi, and how much space you actually need to find.
Hot waterUK coverage
We install air source heat pumps nationwide through MCS-certified regional teams. Grant support differs between England, Wales, Scotland and Northern Ireland, and the regional pages set out what applies where you are.
Get a free, no-obligation quote for heat pump installation in the UK, with the grant deducted so you see the real figure. We come back to you the same working day.