Key takeaways
- Budget £8,000–£14,000 for a typical air-source heat pump install before the £7,500 BUS grant — net £500–£6,500.
- The single biggest determinant of running cost is install quality, not brand. SCOP 3.5+ is achievable; SCOP 2.5 means you'll regret it.
- Sizing should come from a room-by-room heat-loss survey, not a "kW per square metre" rule of thumb. If your installer hasn't measured, walk away.
- You almost certainly need radiator upgrades. Allow £400–£3,000 depending on the property.
- A heat-pump-specific time-of-use tariff (Cosy, Octopus Heat Pump, E.ON Next Heat Pump) is the difference between cheaper-than-gas and not.
- Ground-source only justifies the £20–35K extra cost on properties with land, long tenure, and a willingness to wait 18+ years for payback.
What a heat pump actually does, and why the UK conversation is broken
A heat pump is a refrigeration cycle run in reverse. It moves heat from one place (outside air, the ground, or a body of water) into another place (your home and its hot water cylinder), using electricity to drive a compressor. Because it's moving heat rather than generating it, the energy delivered to your house is typically 2.5–4 times the electricity consumed. That ratio is the coefficient of performance (COP). Averaged over a full UK heating season, it's the seasonal coefficient of performance (SCOP) — and SCOP is the only number that matters for running cost.
The reason the UK conversation is broken is that the technology gets discussed as though it's a like-for-like swap for a gas boiler. It isn't. A boiler runs at 70–80°C flow temperature, heats radiators quickly, and is cheap to fuel because gas is cheap. A heat pump runs best at 35–50°C flow temperature, heats radiators slowly and steadily, and is cheap to run only when it's installed correctly and paired with the right tariff. Treat it like a boiler swap and you'll get a low-SCOP, expensive-to-run system. Treat it like the start of a small heating-system redesign and you'll be fine.
Air-source vs ground-source: the practical comparison
For 95% of UK households the right answer is air-source. Ground-source is a legitimate technology with a higher SCOP ceiling, but the install cost premium is rarely justified by the running-cost difference unless you have specific conditions.
| Factor | Air-source (ASHP) | Ground-source (GSHP) |
|---|---|---|
| Typical install cost (pre-grant) | £8,000–£14,000 | £20,000–£35,000 |
| BUS grant | £7,500 | £7,500 |
| Net cost after grant | £500–£6,500 | £12,500–£27,500 |
| Real-world SCOP (UK) | 2.8–3.6 | 3.8–4.5 |
| External unit needed? | Yes (fan unit) | No (buried loop) |
| Land requirement | None — wall/ground space | Slinky: ~2.5x heated floor area; borehole: ~50–100m deep |
| Disruption at install | 2–5 days | 1–3 weeks (groundworks) |
| Maintenance | Annual service ~£150 | Annual service ~£200 |
| Lifespan | 15–20 years | 20–25 years (compressor); 50+ (loop) |
The honest decision tree: if you have meaningful land (over half an acre is the typical threshold for a slinky loop), expect to be in the property 20+ years, and value the lower running cost and quieter operation, GSHP can make sense. Otherwise, ASHP wins on every practical metric.
Sizing: the calculation that determines everything
Heat pumps must be sized to your heat loss, not your radiators and not your floor area. Anyone who quotes "you need a 12 kW unit because the house is 150 m²" is doing it wrong. The correct method is a room-by-room heat-loss calculation following CIBSE or BS EN 12831, accounting for fabric U-values, glazing, ventilation rate, and the design outdoor temperature for your location (typically -2°C to -4°C in most of England).
For reference, a fabric-improved 3-bed semi (EPC C, cavity insulation, double glazing) typically loses 4–6 kW at design conditions. A pre-improvement Victorian terrace can lose 9–13 kW. A Passivhaus retrofit might lose 1.5 kW.
The implication: undersizing leaves you cold on the worst days. Oversizing causes short-cycling, which kills SCOP and shortens compressor life. Both are common; oversizing is more common because installers default to safety margins.
The flow temperature question
A heat pump's SCOP improves as flow temperature drops. Every 5°C reduction in flow temperature lifts SCOP by roughly 0.2. So a system running at 35°C flow gets SCOP 3.8; the same system at 55°C flow gets SCOP 2.6. The difference in annual running cost is hundreds of pounds.
The catch: lower flow temperature means radiators have to be bigger to deliver the same heat output. Most existing UK radiators were sized for 70°C boiler flow and need to be 1.5–2.2x larger to work at 45°C heat-pump flow. A good installer will model this room-by-room and present a list of radiators that need upsizing. A bad installer will quote without touching the radiators and your system will end up running at 55–60°C flow (and a poor SCOP) just to keep you warm.
MCS accreditation and the BUS grant
The Boiler Upgrade Scheme (BUS) gives £7,500 toward an air-source or ground-source heat pump install. To claim it, the installer must be MCS-accredited and you must own the property (owner-occupiers and private landlords both qualify; new-builds don't).
The BUS application is handled by the installer, who deducts the £7,500 from your invoice and reclaims it from Ofgem. You don't pay then claim back. If an installer asks you to pay the full amount and apply yourself, that's a red flag — they're not properly registered.
MCS accreditation matters beyond the grant. It signals that the installer has been through a competency assessment, follows specified design standards, and the system is covered by the MCS consumer code if things go wrong. A non-MCS install voids most manufacturer warranties and disqualifies you from the grant.
Tariffs: the running-cost lever most homeowners miss
The honest comparison: at flat-rate electricity (28–32p/kWh) and current gas prices (6–7p/kWh), running a heat pump at SCOP 3.0 is roughly cost-neutral with a 88%-efficient gas boiler. At SCOP 3.5+ with a heat-pump-specific tariff, you save 25–40% versus gas.
The tariffs that change the maths in 2026:
| Tariff | Off-peak rate | Off-peak window | Peak rate | Notes |
|---|---|---|---|---|
| Octopus Cosy | ~13p/kWh | 4–7am, 1–4pm, 10pm–midnight (3 windows) | ~38p/kWh (afternoon peak 4–7pm) | Designed around heat-pump cycle; widely used |
| Octopus Heat Pump | ~15p/kWh | Whole-house off-peak rate when paired with smart hardware | Standard rate | Requires compatible heat pump and smart meter |
| E.ON Next Heat Pump | ~19p/kWh | Flat rate, all hours, all year | Same | Simpler — no time-shifting required |
| British Gas Heat Pump | ~21p/kWh | Flat discounted rate | Same | Smaller discount, simpler structure |
The Cosy tariff arithmetic is the most aggressive. If your system can heat a thermal store or pre-heat the building during off-peak windows, you can run the bulk of your heating at 13p/kWh. That makes the effective cost per kWh of heat (electricity-cost ÷ SCOP) approximately 4p — comfortably below gas.
Cost comparison: what you'll actually pay
The implication is straightforward: a heat pump on the wrong tariff is more expensive than gas. A heat pump on the right tariff is meaningfully cheaper. The £7,500 BUS grant pays for itself over 8–14 years on the right setup; over 25+ years on the wrong one.
Brand and unit selection
The major brands available in the UK in 2026, ranked by typical install volume:
- Daikin — Altherma 3 series. Reliable, well-supported, mature controls. Mid-tier price.
- Mitsubishi Electric — Ecodan series. Long UK presence, strong service network. Slight premium.
- Vaillant — aroTHERM plus. Refrigerant R290 (propane), better high-flow-temperature performance. Higher price.
- Samsung — EHS series. Aggressive pricing, decent performance, less mature service network.
- NIBE — F2120 / S series. Strong performance in cold conditions, good for ground-source. Premium price.
- Grant Aerona — UK manufacturer, strong support, often used by smaller installers.
- Worcester Bosch — Compress series. Familiar boiler brand entering heat pump space; install network still developing.
The honest signal: brand matters less than installer competence. A Mitsubishi Ecodan installed by a careless installer outperforms a top-tier Vaillant installed badly. Pick the installer first; let them recommend the brand they know best.
What to ask the installer
The questions that separate good quotes from bad ones:
- "Can I see the room-by-room heat-loss calculation?" — They should produce a spreadsheet or printout showing fabric U-values, ventilation rate, and design temperature for each room. If they wave a kW figure at you with no underlying calculation, walk away.
- "What flow temperature is the system designed for?" — Answer should be 40–50°C maximum. If they say 55–65°C, the SCOP will be poor.
- "Which radiators need upsizing, and what's the cost?" — Should be a specific list. "Probably none" is usually wrong.
- "What's the predicted annual running cost on my tariff?" — They should give you a number and show you how they got there.
- "Are you MCS accredited and can you handle the BUS application?" — Should be a flat yes.
- "What size cylinder, and where will it go?" — Heat pumps need a 200–300L unvented cylinder. If they're keeping your old combi-boiler-fed system, you've got a fundamental mismatch.
- "What controls are you fitting and do they support weather compensation?" — Weather-comp is essential for SCOP. Load-comp via OpenTherm is even better.
- "What's the noise rating at 1m and 4m, and where will the unit sit?" — Modern units run 38–48 dB(A) at 1m. Anything louder and you'll hear it indoors.
Red flags
The patterns that should make you pause:
- "You don't need a heat-loss survey." Every quote should be based on one.
- "We can keep your existing radiators." Sometimes true, usually optimistic. Demand the per-room calculation.
- Quote significantly cheaper than three other quotes. Either an undersized system, the radiator work isn't included, or the installer is cutting corners.
- No discussion of the existing hot-water arrangement. A heat pump needs a different cylinder setup than a combi boiler. If they haven't raised this, they haven't thought it through.
- Pressure to sign before the survey. A proper heat-loss survey takes 2–3 hours; a quote should follow, not precede, that work.
- "You'll be fine on a flat tariff." Technically true, but you'll wonder why you bothered. The tariff conversation should be central.
- External unit positioned in a noise-sensitive location with no acoustic strategy. A unit too close to a bedroom or a neighbour's window is a problem you'll regret.
FAQ
Q: Will a heat pump work in my old/Victorian/poorly insulated home?
A: It will work; whether it works well depends on whether you upgrade radiators and ideally improve fabric first. The "heat pumps don't work in old homes" claim is false — but a heat pump in a leaky home runs harder, costs more, and underwhelms. The right sequence is fabric-first, then heat pump.
Q: How much does a heat pump cost to run versus my current boiler?
A: For a typical 3-bed semi, expect £540–£1,180/year for space heating depending on tariff and SCOP. Gas equivalent is £660–£960. On the right tariff, you save 20–40%. On the wrong tariff, you pay 10–30% more.
Q: How long does the BUS grant take?
A: The installer applies and waits 4–8 weeks for confirmation. They typically deduct it from your invoice up-front, so you don't bridge the cash flow.
Q: Do I need three-phase electricity?
A: No. The vast majority of UK domestic ASHPs run on standard single-phase supply. Some larger units (>16 kW) and most ground-source systems benefit from three-phase, but it's rarely a deal-breaker for typical homes.
Q: How noisy is a heat pump outside?
A: Modern units run 38–48 dB(A) at 1 metre — quieter than normal conversation, comparable to a fridge. At 4 metres it's typically 30–35 dB(A), barely audible. Permitted Development rules limit installations to 42 dB(A) at the nearest neighbour's window, which most modern units meet easily with sensible siting.
Q: Can I have a heat pump alongside my existing boiler (hybrid)?
A: Hybrid systems exist but the BUS grant doesn't apply, and the economics rarely justify the complexity. Either commit to the heat pump fully (with appropriate fabric/radiator work), or stay with gas. Hybrids tend to be a half-measure that capture neither system's full advantage.
Q: What about cold weather — does it stop working?
A: All modern units operate efficiently down to -7°C, and most maintain useful output to -15°C or lower. SCOP drops in cold weather (which is why annual SCOP averages around 3.0–3.5 rather than the headline COP of 4+ at 7°C ambient). The system will keep heating; it'll just consume more electricity per unit of heat output during cold snaps.
Q: How long does an installation take?
A: A straightforward retrofit is 2–5 days on site. If significant radiator work is needed, add another 2–3 days. Ground-source installs are 1–3 weeks because of the groundworks. Disruption is mostly in the plant room and at any radiators being swapped.
If you'd like to size a heat pump for your specific home and model the running cost across different tariffs before committing, the heat pump sizing and tariff calculator on Eco Saving Hub walks through it interactively. Build a personalised plan with realistic SCOP and tariff assumptions at ecosavinghub.co.uk/heat-pump-calculator/ — or, if you'd prefer an independent assessor to walk through the property before you commission quotes, the assessor lookup at healthyhomesnetwork.co.uk/find-assessor/ finds vetted retrofit assessors near you.
Want to model your specific home? Use our free ROI calculators →