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ADVICE CENTRE · QUOTES & BUYING
Why are heat pump quotes so different? A designer opens the black box
Same house, same week — yet the quotes disagree on heat loss, heat pump size, brand, radiators and price, sometimes by thousands. You’re not going mad, and it isn’t random. Here’s exactly where the differences are manufactured, and how to compare quotes like an engineer.
- 13 min read
- Updated July 2026
- By Phil · Heat Loss Hub
QUICK ANSWER
Heat pump quotes differ because each one bundles together things that should be separate: a heat loss calculation (done to wildly varying standards), a sizing decision (coloured by callback fear), a brand choice (coloured by the installer’s supplier terms), a radiator strategy (coloured by margin and time), and a price. Every stage inherits the assumptions of the one before, so small guesses compound into big disagreements. The fix is to separate the engineering from the selling: one independent, measured design that every installer then prices against.
First, the thing that baffles everyone: paying for a calculation just to get a quote
You wouldn’t pay three builders separately to measure your kitchen. Yet heat pump companies routinely ask for £150–£400 for a “survey and heat loss calculation” before they’ll give you a firm price. Why? Because MCS standards require a room-by-room calculation before installation, doing one properly takes hours, and companies burned by free-survey tyre-kickers now charge for it.
The result is quietly absurd: you can pay several times over for several conflicting calculations, each owned by a company whose quote depends on its own numbers being believed. None of them transfers to a competitor. It’s not normal in any other engineering purchase, and it’s most of the reason this consultancy exists — one independent calculation, owned by you, that every installer prices against.
Difference #1: the heat loss — where the divergence is born
Every downstream decision stands on this number, and this is where standards vary most. One surveyor spends three hours with a laser measure and a borescope; another spends twenty minutes and an EPC printout; a third never leaves the office and works from satellite imagery and age-band assumptions.
The assumptions do the damage. Guess “unfilled cavity” where there’s insulation and a wall’s calculated loss doubles. Default to pessimistic air changes and a draught-proofed house gains phantom kilowatts. Use a UK-generic outside temperature instead of your location’s and everything shifts again. Three surveys, three methodologies, three heat losses — 5.9, 9.1 and 11.2 kW for the same Wakefield semi, in one case we documented as a case study. The measured answer was 6.8.
Difference #2: the heat pump size — fear rounds up
From heat loss to unit size, another layer of drift. The installer who’ll own any cold-house complaint adds a margin “to be safe”. The salesperson quotes the model on this month’s best terms. Somebody sizes for hot water recovery with a rule of thumb. A 6.8 kW building becomes an 8, a 10, a 12.
Oversizing isn’t safety — it’s a hidden cost. Big units cycle in mild weather, wear early, and cost more upfront. Our guide What size heat pump do I need? shows how sizing should actually be done: measured loss, design temperature, manufacturer output tables at your flow temperature — no vibes.
Difference #3: the brand — follow the supply chain, not the physics
Installers quote the brands they hold accounts with, trained on, and get rebates from. That’s legitimate business — but it means “the best heat pump for your home” often decodes as “the unit in my van’s usual supply chain”. Physically, several manufacturers make excellent units at every size point; what matters is the specific model’s output and efficiency at your design conditions, its sound levels for your siting, and its controls. An independent design selects from the whole market against those criteria — and documents why. (When manufacturers themselves want independent designs done, they come to consultancies like ours; that should tell you where the brand-neutrality lives.)
Difference #4: the radiator schedule — margin meets methodology
“None need changing” and “all need changing” are both cheaper to say than to verify. The honest answer requires checking every radiator’s output at the proposed flow temperature against its room’s loss — the arithmetic we walk through in the radiator guide. Skip the check and the quote either hides a future efficiency problem (radiators kept, temperature quietly raised) or pads itself with unnecessary steel. When two quotes disagree about your radiators, ask each for the room-by-room emitter table. Watch what happens.
Difference #5: the price — comparing unlike things
By the time five compounding decisions have diverged, the prices describe different projects: different units, different radiator counts, different cylinder sizes, different amounts of unpriced risk. The £9,400 quote and the £14,900 quote aren’t a bargain and a rip-off — they’re answers to different questions. Which is why comparing quotes on price alone is the one strategy guaranteed to mislead.
FIG. 01 — Quotes don't disagree at the end; they disagree at the first assumption and compound from there.
DESIGNER'S INSIGHT
“Here’s the uncomfortable truth from someone who spent 18 years installing: most installers aren’t villains — they’re carrying design risk they were never resourced to carry, in survey slots that were never long enough. The dysfunction is structural. Separate the design from the sale and suddenly everyone behaves better: the numbers get honest, the quotes get comparable, and the good installers finally look as good as they are.”
Phil
Founder & Lead Designer, Heat Loss Hub
How to compare quotes properly — the engineer's checklist
- Demand the room-by-room numbers. A whole-house kW figure with no room breakdown is a guess wearing a suit. No breakdown, no contract.
- Check the design temperature. It should be your location’s recognised figure (around −2 to −5 °C across most of England and Wales), stated explicitly.
- Find the flow temperature. The efficiency claims, radiator schedule and running-cost projection must all use the same one. Mismatches are the classic tell.
- Ask how the unit size was chosen — from manufacturer output tables at your design conditions, or from the model range’s marketing tiers?
- Ask for the emitter table — each radiator’s output at design flow vs its room’s loss. This single request separates engineers from salespeople in one email.
- Normalise the scope — cylinder size, controls, making-good, commissioning detail, grant handling — before comparing a single pound.
- Ignore urgency theatre. Real engineering survives a week of thinking. Expiring discounts are a pricing strategy, not a property of physics.
Or hand the pile to us: an independent design review runs every quote through exactly this checklist, benchmarks the heat losses against your building, and gives you a plain-English verdict — accept, negotiate, or avoid — with the reasoning shown.
Frequently asked questions
MCS requires a room-by-room calculation and sets the methodology — but inputs remain judgment calls (U-values, air changes, room temperatures), surveys vary in depth, and enforcement historically leaned on paperwork more than site verification. The redeveloped MCS scheme is shifting scrutiny toward delivered quality — see our MCS changes explainer — but “compliant” and “identical” will never be the same word.
Averaging three guesses gives you a fourth guess. The middle quote is right only when it’s right — the case-study house’s correct answer (6.8 kW) sat near the bottom of the range. Measurement, not statistics, settles it.
Good ones welcome it — it deletes their unpaid design hours and their risk. Our design packs are produced to the documentation standard MCS installers need, and a small vetted network installs them routinely without alteration. An installer who refuses to price against independent engineering has told you something valuable, cheaply.
Not reliably. Price correlates with brand tier, overheads and margin at least as strongly as with workmanship. Quality shows up in the survey hours, the emitter table and the commissioning spec — all visible before you sign, if you know to ask. Now you do.
CONTENTS
QUOTES IN HAND?
Our independent design review checks every quote against measurement and tells you which one deserves your signature.
END THE CONFUSION
Stop refereeing guesses. Get one measured answer.
Send us your quotes for an independent review, or start fresh with a room-by-room design every installer prices against. Either way, the confusion ends this week.