How much does an air source heat pump cost?

Quick Answer: From £12,300 for a small heat pump to £15,900 for a large one, fully installed, before the grant. After the grant, £3,300 to £8,400.

Heat pumps are sized in kilowatts (kW): the amount of heat they can deliver on a cold day. Most homes need somewhere between 4kW and 16kW.

Quick Answer: Most two and three bed homes need a small to medium heat pump, around £12,300 to £14,100 before the grant. Larger or older homes with more heat to replace sit nearer £14,700 to £15,900.

Nobody knows off the top of their head whether their house needs 6kW or 12kW. So here are some typical homes to help you find one close to yours. They are examples, not real customers.

Quick Answer: Insulation first, because it decides the size of everything else. Then hot water demand, radiators, pipework, where the unit can sit, the brand, and any planning rules on your home.

A well-insulated new build might need around 30 watts of heat for every square metre of floor. A Grade II listed farmhouse with solid walls can need 70 or 80. Same floor area, more than double the heat, and a bigger system.

The full list, in the order it usually matters:

• Insulation, the big one. Loft, walls, glazing and draughts set how much heat your home loses. That number sizes the heat pump, the radiators or underfloor heating, and your running costs for the next twenty years. Walls are usually the biggest loss, and loft insulation is the cheapest thing anyone can do first.
• The size of heat pump. Each step up in size brings a bigger unit and bigger parts.
• Your hot water cylinder. Sized on the number of bedrooms, or the number of people living there if that's higher, at about 45 litres a person a day. A holiday let with a full house every weekend needs far more than a family home. If you have a combi boiler today, you don't have a cylinder yet.
• Your radiators. A heat pump works best at a lower water temperature than a boiler, and the lower it can run, the better. So some rooms need bigger radiators. There's a limit to how big a radiator can sensibly get before it takes over the room, which is one reason insulation comes first. If you care how they look, traditional cast iron designs are available.
• Your pipework. Heat pumps depend on the right flow of water, so your pipework affects how efficiently the system runs. We reuse existing pipework wherever we can.
• Your floors. Suspended timber floors lose heat, so the insulation beneath them affects the cost.
• Where the heat pump can sit. A monoblock heat pump keeps all its refrigerant sealed within the heat pump and sends only warm water into the house, but it wants to sit within about 10 metres of your plant room. A split system sends refrigerant between the outdoor unit and the equipment inside, so the unit can sit much further away, even at the bottom of the garden, and it needs an F-Gas qualified engineer to connect it.
• Listed buildings and national parks. Listed homes and homes on Dartmoor have stricter rules on where the outside unit can go, which can mean longer pipe runs.
• The brand. These prices are for a mid-range heat pump. A premium brand of the same size can add around £3,000 for very similar published performance.
• Your electricity supply. Most homes are fine as they are. Larger properties sometimes have a three-phase supply, and we design to suit what you have.

Quick Answer: Mostly because of size and manufacturer. Three quotes for the same house can recommend three different sizes and brands of heat pump, and the price follows.

We give you an initial estimate first. Then we do a full room-by-room heat loss survey, and that gives you the confirmed design and a confirmed price. Most of the time the survey confirms the estimate. Sometimes the heat pump comes down a size, because we'd rather estimate slightly high than surprise you.

Occasionally it goes the other way. On one barn conversion the estimate said a single 12kW heat pump. The survey found uninsulated solid walls, and the right answer was two 7kW units. It was an awkward conversation, but it happened on paper, before any money was spent.

Getting the size right cuts both ways. On one small, well-insulated home near Exeter, the heat loss came out at just 2.5kW, so the right system was a 4kW heat pump, not the bigger unit an initial estimate would have produced. The performance estimate put its running cost at about £988 a year, against £2,371 for the electric heating it replaced.

Quick Answer: £7,500 off for most homes, or £9,000 if you heat with oil or LPG and have no mains gas. We handle the application for you.

The Boiler Upgrade Scheme is the government paying part of your installation because you're replacing a fossil fuel system. For your home to qualify, the heat pump has to reach a seasonal efficiency (SCOP) of at least 2.8, and the installation must be MCS certified.

Our installations are MCS certified. Our partner, Mere End Consultants, provides independent MCS supervision, checking that the sale, design, installation and commissioning all meet MCS standards, and you receive a valid MCS certificate.

Mere End invoice you directly for MCS registration and certification, insurance and your Boiler Upgrade Scheme application. In line with Ofgem's requirements, the grant is deducted from their quotation, which comes attached to ours.

A fully installed heat pump also currently carries 0% VAT.

Quick Answer: There shouldn't be. The survey finds what your home needs before you commit, so it's in the quote rather than a surprise on the day.

The things the survey checks for, so you know about them up front:

• Radiator upgrades in rooms that need them.
• Electrical work, occasionally including a new consumer unit in an older home.
• A base for the outside unit, and UV-resistant pipe lagging outside. We supply the insulation ourselves so MCS sign-off never fails on it.
• A day or two without hot water while the cylinder is swapped. We tell you which days.

Radiator upgrades and electrical work are included in our prices.

One cost sits outside our quote: our MCS partner's certification fee, currently £825 plus VAT, which Mere End invoice you for directly. It isn't an optional extra. MCS certification is what triggers your grant, so without it there is no grant.

Quick Answer: Much cheaper than oil, LPG or old electric heating. Against a working gas boiler, running costs are currently about level, and your insulation decides which way it tips.

Efficiency is measured as SCOP, the seasonal coefficient of performance. A SCOP of 3 means you get three units of heat for every unit of electricity the heat pump uses. A poorly insulated house might sit just above 2.8. A well-insulated one can reach 4.5 or 5. Before you decide, you get a quick performance estimate showing the likely running cost, and a more accurate one once the full room-by-room design is done.

You will probably get more than one quote, and you should. Take this checklist to every installer, us included:

1. What size of heat pump is recommended, and how was it worked out?
2. Is every radiator checked against its room, with any changes listed and priced?
3. Is the hot water cylinder named, with its size?
4. Is it a mid-range or a premium heat pump?
5. Has the grant already been deducted, as the scheme requires?

Once every quote answers those five, you're comparing like with like, and the prices will make much more sense.

If a few hundred pounds of loft insulation would let you buy a smaller, cheaper heat pump that costs less to run every year after, do the insulation first.

Tell us about your house using the form. We'll come back with a realistic estimate based on the way we actually price jobs, and if the right answer is 'not yet', you'll hear that too.