Working file V5
Deep retrofit vs heat pump only (UK 2026)
Deep retrofit vs heat pump only (UK 2026): side-by-side decision aid with capex, grant treatment, payback shape and surveyor's note.
| Dimension | HP-only | Phased deep |
|---|---|---|
| Gross capex | £10,150 to £19,450 | £35,000 to £70,000 |
| Grant offset | £7,500 BUS | BUS + ECO4 (if eligible) + GBIS + 0% VAT |
| Net capex | £2,650 to £11,950 | £23,000 to £55,000 |
| Published post-grant prices | £4,064 to £6,729 | Nobody publishes one |
| Running-cost change at the Q4 2026 cap | Minus £43 to plus £249 a year | Not modelled here |
| Carbon-delta | Largest single step | Reaches EPC A trajectory |
The gross capex column is this file's coefficient stack: an air-source heat pump at £8,000 to £14,000, a radiator upsize at £1,800 to £4,500 and controls at £350 to £950. The published post-grant row is what three suppliers actually print (Octopus £4,064, E.ON Next from £4,946, Aira £6,729), and it sits in the lower half of the modelled net band, which is the sort of check worth doing before signing either quote. The running-cost row is the fuel switch alone at a £900 gas bill, across the boiler-efficiency and SPF bands in the published evidence; the negative end is real, not a rounding artefact.
Payback ribbonYears to break even, at the Q4 2026 Ofgem cap.
runs past 20 yr →
ECO4 cliff
BUS end (2030)
0 yr5 yr10 yr15 yr20 yr
Heat-pump leg only: sixteen years at the most favourable end, forty to sixty-seven at the national trial's median SPF, no break-even in the bottom quartile. No figure is published for the deep column, because this file does not model the demand its fabric and solar legs remove.
Surveyed 1 October 2026. Ofgem cap for 1 October to 31 December 2026 applied (gas 7.97p, elec 26.32p, gas standing 29.68p, elec standing 54.83p). Next scheduled review 25 November 2026 (January cap announcement). [ref V5]
By Oliver Wakefield-Smith, Founder, Digital Signet. Corrections to oliver at digitalsignet dot com.