Home / Case Studies / 1930s Semi, Wakefield
CASE STUDY · FULL INDEPENDENT DESIGN
Three quotes, three stories, one measurement: a 1930s semi in Wakefield
How a family with quotes ranging from 5.9 kW to 11.2 kW — and radiator advice from “keep them all” to “replace the lot” — ended up with a measured 6.8 kW design at 45 °C flow, seven of ten radiators retained, and an installation that matched the drawings to the millimetre.
- 14 min read
- Project completed winter 2025–26
- Location: Sandal, Wakefield
6.8 kW
Measured heat loss at −3.2 °C — against quotes of 5.9, 9.1 and 11.2 kW
45 °C
Design flow temperature — with weather compensation below it most of the winter
7 of 10
Existing radiators retained after room-by-room output checks
£7,500
Boiler Upgrade Scheme grant claimed and processed by the installer
The initial problem: three quotes that couldn't all be right
The homeowners — a family of four in Sandal, on Wakefield’s southern edge — came to us the way most people do: confused, slightly annoyed, and holding paperwork that contradicted itself. They’d done everything the consumer advice says. Three quotes from three MCS-certified companies. And the result was chaos:
THE THREE QUOTES AS RECEIVED — SAME HOUSE, SAME FORTNIGHT
| Quote A (regional installer) | Quote B (national brand) | Quote C (local firm) | |
|---|---|---|---|
| Claimed heat loss | 9.1 kW | 5.9 kW | 11.2 kW |
| Survey method | 45-minute walkround | Desktop / EPC data | “Satellite-assisted assessment” |
| Proposed unit | 10 kW | 6 kW | 12 kW |
| Radiators | Replace 6 | Replace none | Replace all 10 |
| Flow temperature | 50 °C | Not stated | 55 °C |
| Price after grant | £8,900 | £5,400 | £11,700 |
Quote B’s price was tempting. Quote C’s salesperson was persistent — a “survey-week discount” expired, was extended, and expired again. The family’s instinct said something was off but couldn’t say what. They found our guide to conflicting quotes at 11pm on a Tuesday, and the enquiry arrived overnight: “Can someone just tell us the truth about our house?”
The property
Survey findings: what three hours with a LiDAR scanner turns up
The technical survey took just over three hours. The findings that mattered:
- The cavity was filled. Drill-tested at two discreet points and confirmed with a borescope: blown mineral fibre, 1990s vintage, in decent condition. Quotes A and C had both assumed unfilled cavities — instantly explaining two to three “phantom” kilowatts in their figures.
- The bay lounge was the genuine problem room. Suspended floor with a ventilated void, flat bay roof with unknown (thin) insulation, three exposed orientations — measured loss 1,410 W, the largest in the house by half.
- Ventilation was better than defaults. The 2003 window refit had draught-sealed effectively; the one open chimney had been swept and capped years earlier. Standard air-change assumptions would have overstated the house by ~15%.
- The cylinder question had a friendly answer. The combi conversion had left the original airing cupboard intact — a 210-litre cylinder would fit with 40 mm to spare (measured, not hoped).
- Microbore, but survivable. Three upstairs radiators ran on 10 mm microbore. Flow-rate calculations showed two were fine at design conditions; one — the main bedroom — needed its final run upsized during installation.
- Siting was easy. The side return by the garage gave the outdoor unit a home 4.2 m from the nearest neighbouring window, passing the sound assessment with 6 dB of headroom.
The heat loss calculation
Every room measured by LiDAR, every construction assigned a verified U-value, ventilation set room by room, design condition −3.2 °C for the site. Whole-house result: 6.8 kW — with the room-level detail that actually drives design:
ROOM-BY-ROOM RESULTS (ABRIDGED) — LOSSES AT −3.2 °C OUTSIDE, DESIGN ROOM TEMPERATURES
| Room | Heat loss | Existing radiator | Output @ 45 °C flow | Verdict |
|---|---|---|---|---|
| Lounge (bay) | 1,410 W | K2 600×1100 | ≈ 700 W | Replace — K3 600×1400 |
| Kitchen/diner | 1,020 W | K2 600×1000 + kickspace | ≈ 810 W | Replace — K3 600×1000 |
| Hall & landing | 760 W | K1 600×900 | ≈ 300 W | Replace — K2 600×1100 |
| Bedroom 1 | 640 W | K2 600×1100 | ≈ 700 W | Retain |
| Bedroom 2 | 520 W | K2 600×900 | ≈ 570 W | Retain |
| Bedroom 3 | 330 W | K1 600×800 (1987 vintage) | ≈ 350 W | Retain — 1987’s pessimism pays off |
| Bathroom + others | 2,020 W combined | Various | Adequate | Retain (towel rail supplemented by design margin) |
Note the pattern we describe in the radiator replacement guide: the living spaces and hall fall short at low flow temperatures; the bedrooms sail through. Three changes — not zero, not ten.
Design challenges
Three genuine engineering tensions emerged from the survey — the kind that don’t appear on a quote until they appear on an invoice. Each pitted an upfront cost against a running cost, which is exactly where an independent designer earns their fee: we have no stake in either side of that trade, so the arithmetic gets to decide.
Technical decisions
- The bay lounge vs the whole-house flow temperature. At 50 °C the existing lounge radiator almost passed — the temptation was to run the entire system hotter to save one radiator swap. The arithmetic said no: 5 °C on the flow temperature costs roughly 10–12% efficiency on every kWh the house ever uses, against a one-off £340 radiator. The radiator lost.
- Hot water recovery with two teenagers approaching. A 6 kW unit could heat the house, but cylinder reheat after back-to-back showers would lean on the immersion at peak rate. The 7 kW unit’s extra coil headroom reheated the 210 L cylinder 25 minutes faster — worth having, verified against manufacturer data rather than guessed.
- Microbore diplomacy. Full repiping would have added ~£1,800 and two days of floor lifting for marginal benefit. Flow-rate calculations justified keeping two runs and upsizing one — the design documented exactly which, so installation day involved no discovery.
DESIGNER'S INSIGHT
“Quote B deserves a moment of sympathy: its 5.9 kW wasn’t far from our 6.8 — closer than the two ‘bigger’ surveys. But it got there by luck, not measurement, and luck doesn’t size cylinders or spot microbore. A nearly-right number with no room-level detail behind it is still an unbuildable design. That’s the part price comparisons never show.”
Phil
Founder & Lead Designer, Heat Loss Hub
The final design
Installation outcome
The family chose an installer from our vetted network. Because the design answered every question in advance, the installation ran to three and a half days without a single variation: no surprises under the floor, no “while we’re here” upsells, no re-engineering at the kitchen table. The installer claimed the £7,500 Boiler Upgrade Scheme grant and handled DNO notification and MCS certification paperwork. Commissioning followed the design sheet — curve set, system balanced, hot water scheduled — and we reviewed the commissioning data against the design before sign-off.
First winter’s verdict, from the client’s follow-up email in March: “Every room warm, including the bay lounge for the first time since we moved in. February’s electricity bill for everything — heating, hot water, the lot — was £148. The old gas bill alone was more.” Measured performance over the first full season tracked the projection within a few percent — SCOP just above 4 — exactly where a 45 °C design should land.
Lessons learned
- The truth was cheaper than two of the three guesses. The measured design, installed, cost £2,100 less than Quote A and £4,900 less than Quote C — while out-specifying both on cylinder, controls and documentation.
- Verification beats assumption twice over. One borescope hole through a mortar joint deleted 2.3 kW of phantom heat loss. Minutes of checking; thousands of pounds of consequence.
- The worst room sets the system’s temperature — so fix the worst room. One K3 radiator in a bay window bought the whole house 45 °C operation.
- 1987’s oversized radiators are 2026’s free upgrade. Bedroom 3’s ancient, generously sized K1 passed at low temperature untouched. Old pessimism is retained value — if someone checks.
- Design-first changes the installer relationship. Same trade, same tools — but with the engineering settled, the installer’s craft got to shine and the homeowner never faced a doorstep decision.
If your kitchen table looks like theirs did — contradictory quotes, expiring discounts, growing doubt — start where they did: an independent review of what you’ve been given, or go straight to the full measured design.
CONTENTS
YOUR HOUSE NEXT?
Every project starts the same way — a short enquiry, reviewed personally, answered honestly.
YOUR PROJECT, MEASURED
Every confused kitchen table is one survey away from clarity
Tell us about your home and what you’ve been quoted so far. We’ll review it personally and reply by email with the honest next step.