Methodology

This page explains how ASHPCost sources, reviews, and updates the data on our site. We publish it because anyone making a four- or five-figure home improvement decision deserves to know where the numbers came from.

Data sources

Statistical claims on this site are derived from one or more of the following authoritative sources, cited inline where used:

• Energy Saving Trust UK heat pump trial — Multi-year EST field trial of UK heat pump performance and SCOP — used to validate our running-cost figures.
• Ofgem BUS installation statistics — Monthly vouchered installation count by region and property type — used to weight our regional pricing.
• ONS Domestic Energy Bills Survey — Office for National Statistics household energy expenditure survey — used as the baseline for running-cost comparisons.
• Octopus Cosy / EDF Heat Pump tariff sheets — Live heat-pump-specific time-of-use tariffs — used to model running cost when a heat-pump-friendly tariff is selected.

Cost-data sourcing (where applicable)

Where we publish installed-cost ranges (e.g. "a typical UK semi-detached costs £9,500–£13,500 before grant"), the ranges are derived from real installer quotes shared by homeowners with us, anonymised and cross-referenced against Energy Saving Trust and Ofgem published averages.

• Quote pool: 420+ quotes collected between October 2025 and March 2026 across England, Scotland and Wales.
• Anonymisation: All identifying data (homeowner name, postcode, contact details) is stripped before quotes enter the cost-band calculation.
• Outlier handling: The lowest 5% and highest 5% of quotes are excluded — these are typically misquotes, package deals with unusual scope, or extreme retrofit cases.
• Refresh cadence: Cost ranges are recalculated quarterly. The published date at the top of cost-data pages reflects the most recent refresh.

Technical review

Pages that include sizing, install-process, or running-cost claims are reviewed by an MCS-qualified UK heat-pump installer before publication. The reviewer checks:

• kW-sizing ranges per property type are consistent with current MCS heat-loss survey practice.
• Install timeline ranges reflect a representative UK install, not best-case or worst-case outliers.
• Quoted SCOP figures (heat-pump efficiency) match the manufacturer-published values for representative current-model units (Daikin Altherma, Vaillant aroTHERM, Mitsubishi Ecodan, Samsung EHS).
• Grant eligibility criteria match the most-recent published BUS scheme rules at gov.uk.

Updates and corrections

Material changes to BUS grant rules, MCS standards, or significant Ofgem-published data trigger a full review of affected pages within 14 days. See our Editorial Policy for the corrections process and how to flag an error.

What we don't do

• We do not publish manufacturer-supplied marketing figures (SCOPs measured under unrealistic test conditions, "up to 80% bill saving" claims, etc.).
• We do not accept payment to adjust published cost ranges, installer rankings, or comparison verdicts.
• We do not republish AI-generated content as our own. Where we use AI-assisted research or drafting, the output is reviewed and edited by a human before publication.

Spotted an error?

Email hello@ashpcost.co.uk with the page URL and the issue. We acknowledge within 2 working days and publish a correction (with a dated note) within 14 days for material errors.