An air source heat pump extracts heat from outside air — even in freezing weather — and moves it into your home through radiators, underfloor heating and a hot water cylinder. Done properly, it replaces your boiler outright: same warm rooms, same hot showers, no flame, no flue, no fuel deliveries. Done badly, it's the source of every horror story you've read. The difference between the two isn't the heat pump. It's the design work before anyone lifts a spanner — and that's what this page explains.
What a Properly Designed Installation Involves
MCS rules require heat pumps to be sized from a room-by-room heat loss calculation, not a rule of thumb based on your old boiler. We measure every room: floor area, ceiling height, wall construction, glazing, and air leakage, then calculate how much heat each room loses on a design-condition winter day (around −2 °C outside for Buckinghamshire, with living rooms held at 21 °C). The heat pump is sized to that total. This matters in both directions: an undersized unit can't keep up in January, while an oversized one cycles on and off, wears itself out and runs inefficiently. Most homes we survey need between 5 kW and 12 kW — and the number that matters is yours, not an average.
The same calculation drives radiator sizing. Heat pumps run most efficiently at flow temperatures of 35–45 °C rather than the 70 °C a boiler blasts out, so each radiator must be big enough to deliver its room's heat at the lower temperature. In practice most homes keep the majority of their radiators; a handful get upsized. Your survey lists exactly which, and the cost is itemised in the quote rather than discovered on install day.
Because a heat pump doesn't heat water on demand the way a combi does, you'll have a hot water cylinder — typically an unvented cylinder sized at roughly 45 litres per person, with a large coil designed for heat pump flow temperatures. It heats overnight or on cheap-rate electricity and holds enough for back-to-back showers. Finally, controls: we commission every system with weather compensation, which adjusts the flow temperature continuously against the outdoor temperature instead of hammering on and off at a fixed setting. It's the single biggest difference between a system that achieves its designed efficiency and one that doesn't.
Equipment choice comes last, not first. Once the numbers exist, we specify a unit from manufacturers whose UK parts and service networks we trust, sized to modulate comfortably at your house's typical load rather than its worst-case day. Every unit we fit carries a manufacturer warranty of 5–7 years alongside our own workmanship guarantee, and the MCS registration we lodge at handover is what keeps both enforceable.
What It Costs in 2026
An installed air source heat pump system in Buckinghamshire typically costs £9,000–£14,000 before grant support, depending on heat pump size, how many radiators need changing, cylinder requirements and pipework. VAT on installation is 0% until 2027, and the Boiler Upgrade Scheme grant comes off the price before you pay anything:
| Typical project | Before grant | After £7,500 grant | After £9,000 grant* |
|---|---|---|---|
| 3-bed semi, few radiator changes | £9,000–£10,500 | £1,500–£3,000 | £0–£1,500 |
| 4-bed detached, cylinder + several radiators | £10,500–£12,500 | £3,000–£5,000 | £1,500–£3,500 |
| Large rural detached, bigger unit + pipework | £12,500–£14,000 | £5,000–£6,500 | £3,500–£5,000 |
What's included in every quote: the heat loss report, the heat pump and outdoor base, cylinder, radiator changes, controls, electrical work, commissioning, MCS registration and the paperwork pack your warranty and grant depend on. What's never included: a price plucked from a phone call. If a company quotes you without measuring your rooms, they're guessing with your money.
On running costs, the number to ask any installer for is the design SCOP — the seasonal efficiency the system is expected to achieve across a whole year. A well-designed system in this area should reach a SCOP of 3.5–4.0, meaning every 1 kWh of electricity delivers 3.5–4 kWh of heat. Pair that with a dedicated heat pump electricity tariff (several suppliers now price overnight and heat pump usage at 15–20p/kWh) and most oil-heated homes come out ahead of their old fuel bills — our running costs vs oil guide shows the arithmetic line by line.
The Boiler Upgrade Scheme, Applied to Your Quote
The Boiler Upgrade Scheme is a government grant of £7,500 towards an air source heat pump — rising to £9,000 for oil and LPG heated homes from 21 July 2026 until March 2027. It's installer-led: you don't apply for anything. We confirm your eligibility at the survey (you own the property, it has a valid EPC with no outstanding loft or cavity insulation recommendations, and the heat pump fully replaces a fossil fuel or electric heating system), apply to Ofgem on your behalf, and show the grant as a deduction on your quote. You pay the difference and we redeem the voucher after commissioning. The grant hub covers eligibility in detail, including the rules for second homes and rental properties.
Will It Work in an Older Bucks Property?
Yes — the question is design, not possibility. Older solid-wall homes need a bigger unit and some larger radiators, occasionally a high-temperature model. For the grant, only outstanding loft and cavity wall EPC recommendations must be cleared; solid walls never have to be insulated. The detail, honestly:
Honest answer: it depends on heat loss, not age. A heat pump will heat any house — the question is how large a unit and which radiators it takes to do it efficiently, and that's driven by insulation. A 1970s house with cavity wall insulation and a decent loft usually converts easily. A solid-wall Victorian cottage in a North Bucks village loses more heat, so it needs a more careful design: sometimes larger radiators and a bigger unit, sometimes modest insulation work first, and occasionally a high-temperature heat pump that runs radiators at boiler-like temperatures where the fabric can't reasonably be upgraded.
Two things we tell every period-property owner up front. First, the grant requires loft and cavity insulation recommendations on your EPC to be dealt with — solid walls don't have to be insulated, which is a common misconception that stops cottage owners applying. Second, running costs in a draughty house will be higher with any heating system; the survey tells you what they'll be before you commit, not after.
We've written more on all of this: do heat pumps work in old houses? covers solid walls, radiator upgrades and the insulation-first logic; the consent process for listed buildings and conservation areas has its own section in the planning guide; and the running costs guide shows full workings against oil, LPG, gas and electric heating.
Noise and Placement Rules
Modern units are quiet — around 40–60 dB(A) at the unit itself, roughly a fridge to a quiet conversation, and much less by the time it reaches a neighbour's window. Most installations qualify as permitted development, meaning no planning application, provided the MCS 020 noise assessment shows no more than 42 dB(A) at the nearest neighbouring assessment position and the outdoor unit stays within size limits (1.5 m³ including its housing). The old rule requiring one metre from the boundary was scrapped in England in May 2025, which opened up siting options for semis and cottages with narrow side passages.
We run the noise assessment for every installation as standard and choose the position accordingly — usually a rear or side wall on a solid base, away from bedroom windows, with pipe runs kept short. If your home is listed or in a conservation area, different rules apply to the outdoor unit's siting.
The full rules, including what happens if 42 dB can't be met and when planning permission is needed, are in our planning permission guide — and for the real decibel numbers, R290 units and placement tactics, see the heat pump noise guide.
Our Process
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Survey
A room-by-room heat loss calculation at your home, radiator schedule and cylinder assessment. Free, and the report is yours to keep whoever you choose.
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Design & quote
Unit, cylinder and emitter selection matched to the numbers, with a fixed price showing the grant already deducted. No allowances, no "extras to be confirmed".
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Install
Typically two to three days. Old boiler decommissioned, system installed, pressure-tested, commissioned and balanced, and the controls explained properly before we leave.
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Grant & handover
We handle the Ofgem voucher, register the system with MCS, and hand over your certificate, warranty and building regulations documents.
Air Source Heat Pump Questions
Does an air source heat pump work when it's freezing outside?
Yes. Heat pumps are standard heating in Norway and Sweden, where winters are far colder than a Bucks frost. Modern units keep working below −20 °C; efficiency dips on the coldest days but the system is sized for exactly those conditions — that's what the −2 °C design calculation is for. The unit briefly defrosts its outdoor coil in cold, damp weather, which is normal and automatic.
What size heat pump will my house need?
Whatever the heat loss calculation says — typically 5–8 kW for semis and smaller detached homes, 8–12 kW for larger detached houses, occasionally more for big rural properties. Beware anyone sizing from bedrooms or boiler size: boilers are habitually oversized, so "like for like" bakes in the wrong number.
Do I need underfloor heating for it to work?
No. Underfloor heating suits heat pumps beautifully because it runs at low temperatures, but correctly sized radiators achieve the same thing. Most of our installations run entirely on radiators, with a few strategic upsizes identified at the survey.
How long does the installation take?
Most installations take two to three days on site: day one for the outdoor unit, cylinder and pipework, day two for radiator changes and electrics, and commissioning to finish. You'll usually be without heating and hot water for less than a day in the middle.
What maintenance does it need, and how long will it last?
An annual service — filters, refrigerant checks, water treatment — much like a boiler service, and required to keep most manufacturer warranties valid (typically 5–7 years). Well-maintained heat pumps routinely last 15–20 years, longer than the average boiler, partly because they work far less hard than a boiler running at 70 °C.
Start With the Survey, Not a Sales Call
Every good heat pump starts with an honest set of numbers. Book a free room-by-room heat loss survey and you'll get a fixed quote with the Boiler Upgrade Scheme grant already deducted — and a report that's yours to keep even if you never speak to us again.