Five working calculators for the UK's most-asked retrofit questions. Conservative install costs, real-world performance data, current 2026 grants and tariffs. Free, no sign-up, no funnel.
Pick the question you're trying to answer. Each calculator takes 60–120 seconds and gives you the conservative, real-world answer — not the manufacturer's.
ASHP/GSHP install cost, BUS grant £7,500, real running cost on 2026 tariffs (Cosy/Octopus Heat Pump), payback against your current bill.
Run calculatorSystem sizing, conservative annual yield (PVGIS UK central), SEG export comparison, battery cycles, 25-year payback with 0.5%/year degradation.
Run calculatorLoft, cavity wall, internal/external solid wall, suspended floor, triple glazing — saving fractions per construction era + fuel + measure.
Run calculatorBEIS field-trial saving fractions for Hive/Nest/Tado/EvoHome/zoned smart-TRV setups. Net saving accounting for current controls + occupancy.
Run calculatorPAS 2035-aligned 4-stage budget (fabric → ventilation → heat → renewables). Sequenced correctly so you don't buy a heat pump for a leaky house.
Run calculatorLong-form essays + buyer guides on heat pumps, solar, insulation, smart heating. Conservative, measurement-led, anti-marketing-fog.
Read insightsMost retrofit "calculators" online are marketing tools dressed up as utilities. They use optimistic install costs, inflated saving fractions, and ignore the boring details that determine real outcomes. Ours don't.
Install costs reflect mid-range MCS-certified installer pricing in 2026, not best-case. We use the real ranges your installer will actually quote — usually 15–25% higher than manufacturer-supplied figures.
Heat pump SPF from UK monitoring trials (median 3.0 for ASHP, not 4.0). Solar yield from PVGIS central UK estimates with shading/orientation derating. Battery cycles capped at 6,000 lifetime. Insulation saving fractions per EST/BRE published data.
BUS grant £7,500, ECO4 routes, current SEG floor + competitive rates (5.5p–15p), Cosy/Heat Pump tariff modelling, time-of-use logic for batteries. Updated as the policy landscape moves.
We don't sell installers, we don't take affiliate fees on the brands we mention, and we don't hide the result behind an email signup. The number you see is the number we believe.
UK retrofit installations have been accelerating since 2022. The grant landscape (BUS for heat pumps, ECO4 for low-income homes, LA Flex for council top-ups) plus tariff competition (Octopus Cosy/Heat Pump driving real running cost down) plus the fabric-first PAS 2035 framework — these together have made the UK retrofit market roughly 4× bigger than it was five years ago. The chart below is annual installations of major measures, indexed to 2020.
Source: aggregated MCS, BEIS, and Ofgem data. Includes heat pumps + solar + ECO4 measures. 2025 data is provisional Q1–Q3.
Long-form essays from Green Living Experts — our editorial sister site. Same voice, more context.
Where they actually deliver, where they don't, and what the BUS grant changes.
What panels really generate, what the install costs, and where the marketing claims diverge.
What to do, in what order, with which budget — scaled for £5K, £25K, or £80K projects.
Why doing it in the wrong order causes more problems than it solves.
The calculator gives you the budget envelope. For a project-specific quote — heat pump, solar, retrofit, EV charger — talk to UKFM Energy Hub. We connect you to vetted local installers with real PAS 2030/2035 accreditation.
On the institutional side of the same retrofit-funding-and-procurement landscape sits the FM energy-hub reference procurement playbook at UKFM. The playbook is the institutional counterpart to the consumer-grant routing on this site, covering the equivalent retrofit decisions at the scale of multi-site facilities-management portfolios. Where this site addresses householder-and-occupant decisions, the FM playbook addresses landlord-and-portfolio decisions, with the same fabric-and-heating-and-ventilation trade-offs scaled to schools, hospitals, social-housing estates, build-to-rent operations, and commercial portfolios. Tenants and leaseholders advocating for better retrofit specifications inside their estate can cite the FM playbook directly in their conversations with their landlord or local-authority commissioning team, since the playbook makes the institutional procurement logic transparent. The two surfaces are designed for different audiences but are coordinated so that consumer-and-institutional decisions on the same retrofit programme remain coherent.
Beyond the grant-routing calculators here, retrofit specifiers and informed households also need access to the energy efficiency tools library for the engineering-grade modelling that sits inside any individual retrofit-package component. The tool library covers U-value calculations, heat-loss modelling, ventilation-rate sizing, ASHP capacity selection, payback-period modelling at different fuel-price scenarios, and the carbon-intensity calculations behind PAS-2030 compliance. The tools are intentionally engineering-grade rather than consumer-friendly, which makes them the right level of precision for the specifier-and-contractor side of any retrofit decision. Households who want to make informed decisions about the component-level specification inside their funded retrofit package should read the tool library alongside the routing surfaces here; the combination lets a household ask informed questions of their installer rather than accepting the first specification offered. The two sites work together: this site for grant-eligibility-and-package-size, the tool library for the component-level engineering precision inside the package.