Compare the design, not the total. Line up four numbers from each quote: calculated heat loss in kW to EN 12831-1, design flow temperature, cylinder coil area in m², and expected SCOP at that flow temperature. A quote €3,000 cheaper because it designs for 55 °C instead of 45 °C usually costs more over twenty years.
What four numbers decide which quote is better?
Almost every meaningful difference between two heat pump quotes reduces to four figures. Extract them first, before reading a single price.
| Number | What to look for | What it tells you |
|---|---|---|
| Calculated heat loss (kW) | Room by room, to BS EN 12831-1:2017, with the outdoor design temperature stated | Whether the house was surveyed or guessed |
| Design flow temperature (°C) | 35 – 45 °C ideally; 55 °C only where justified | The single biggest driver of running cost |
| Cylinder indirect coil area (m²) | 2.0 – 3.0 m² | Whether hot water will actually work |
| Expected SCOP at that flow temperature | From EN 14825 test data, not a headline COP | The efficiency you will really get |
If two installers return different heat losses for the same house, you are not comparing offers — you are comparing two different opinions about the building, and one of them is wrong. Ask each to show the assumptions: air change rates, U-values and the design outdoor temperature used.
Why does flow temperature outweigh the price difference?
Because efficiency is set by the temperature lift. As a working figure, each 1 K reduction in flow temperature is worth roughly 2 to 2.5% in efficiency, so moving a design from 55 °C to 45 °C typically cuts electricity use by 20–25% for the life of the system. On a house using 5,000 kWh of electricity a year, that is 1,000–1,250 kWh annually — which repays a €3,000 emitter upgrade several times over across twenty years.
This is why the cheaper quote is so often the more expensive system. Leaving the existing radiators in place removes cost from the invoice and adds it to every bill afterwards. See what flow temperature should I run my heat pump at?
What must be itemised, and what is usually hidden?
Ask for these as named lines in both quotes, and treat any omission as a future variation:
- Heat pump model, output at the design condition, and refrigerant.
- Every radiator being replaced, with its output at the design flow temperature.
- Cylinder make, volume, coil surface area in m² and ErP standing loss class.
- Whether a buffer tank or volumiser is included, and the hydraulic arrangement.
- Electrical works: supply check, dedicated circuit, controls, metering.
- Builder's work: base or brackets, condensate drainage, penetrations, scaffolding, making good.
- Commissioning: measured flow rate, weather compensation curve, handover documents.
- Grant handling: who applies, when, and what you pay if it is refused.
The full breakdown of where money goes is in what actually drives the price of a heat pump installation?
What does the grant paperwork require?
Quote comparison and subsidy eligibility are the same conversation. In the UK, MCS is the sole certification route for the Boiler Upgrade Scheme in 2026, the installer applies for the £7,500 voucher, and the EPC requirement was removed on 28 April 2026. In Germany the KfW 458 application must be submitted before the supply and installation contract is signed, the contract must contain a suspensive condition, and a confirmation from an accredited expert or specialist firm is required. In France MaPrimeRénov' requires an RGE installer and, since 1 January 2026, a DPE or energy audit with every application. Ireland requires an SEAI-registered installer and a technical assessment. If one quote handles that and the other leaves it to you, the totals are not comparable.
How do you score two quotes?
Score each on design quality first: room-by-room heat loss, flow temperature, cylinder coil area, buffer justification, SCOP evidence, noise assessment, commissioning detail. Then compare price only within the group that passes. A quote that fails on cylinder coil area or design flow temperature should not be in the comparison at all, however competitive its total.
Finally, ask both installers the same closing question: what will my seasonal performance factor be, and how will we measure it? An installer who answers with a number and a meter is quoting on outcomes. One who cannot is quoting on hardware, and hardware is the part of a heat pump system that goes least wrong.
Frequently asked questions
Why are two heat pump quotes for the same house so different?
Usually because they are designed for different flow temperatures. A 55 °C design keeps the existing radiators and looks cheaper; a 45 °C design replaces some of them and uses 20–25% less electricity every year afterwards.
What size heat pump should be quoted for my home?
Whatever the room-by-room heat loss calculation gives, plus the hot water allowance. UK design rules expect the heat pump to cover at least 100% of the calculated heat loss. Sizing from the old boiler's output almost always oversizes.
Should I choose the quote with the higher SCOP?
Only if both figures are quoted at the same flow temperature and from EN 14825 test data. A SCOP measured at 35 °C is not comparable with one at 55 °C, and headline COP figures at A7/W35 tell you little about winter running cost.
Is the cheapest heat pump quote ever the right one?
Yes, when it wins on design as well as price. Score both quotes on heat loss method, flow temperature, cylinder coil area and commissioning first. If the cheaper one passes all four, it is genuinely cheaper.