Working file C4
Retrofit payback period at Q3 2026 Ofgem cap (UK)
Payback years for an ASHP and for a phased deep retrofit, at Ofgem Q3 2026 unit rates (gas 7.33p, electricity 26.11p, gas standing 29.04p).
The math, plainly
Annual saving is current gas spend (or estimated gas kWh times 7.33p) minus new running cost (estimated heating kWh divided by a SCOP of around 3.2, times 26.11p). Standing-charge differences are netted at the meter. Payback is net-after-grant capex divided by annual saving.
Payback ribbonYears to break even, at Q3 2026 Ofgem cap.
ECO4 cliff
BUS review (~2028)
0 yr5 yr10 yr15 yr20 yr
7 to 15 years to break even at the Q3 2026 Ofgem cap.
Where payback collapses
SCOP delivered under 2.6 (poor low-temp design, oversized rads not delivered), high standing charges on a single-rate tariff, fabric not addressed first. The Heat Geek delivered-SCOP dataset is the cleanest public reference point for the design-quality lever.
Surveyed 22 June 2026. Ofgem Q3 2026 cap applied (gas 7.33p, elec 26.11p, gas standing 29.04p). Next scheduled review 26 September 2026 (Q4 cap publication). [ref C4]
By Oliver Wakefield-Smith, Founder, Digital Signet. Corrections to oliver at digitalsignet dot com.