How We Calculate Costs: Our Methodology

Quick answer: Every modelled cost on Green Reach Energy starts from a national installed-price baseline for each product, is adjusted by a 12-region labour index (0.92 to 1.20), and is given a typical range of 0.65× to 1.55× the mid-point. Running costs use the July–September 2026 Ofgem price cap: 26.11p/kWh electricity, 7.33p/kWh gas.

This page is the methodology behind our UK Home Energy Cost Index and the savings calculator. It was last reviewed in July 2026. We publish it in full because a cost estimate you cannot interrogate is just a guess with confidence.

The inputs

• National installed-price baselines. For each of the eight products we track, we maintain a single national mid-point figure for a typical domestic installation — for example £11,014 for an air source heat pump and £6,496 for solar panels in July 2026 — compiled by desk research across published installer pricing, industry price guides and Energy Saving Trust cost ranges.
• Regional labour indices. Installation is labour-heavy, so we apply a multiplier for each of the 12 UK regions, from 0.92 in Northern Ireland to 1.20 in London, reflecting relative trade labour rates.
• Energy prices. All running-cost and savings arithmetic uses the current Ofgem price cap — 26.11p/kWh for electricity and 7.33p/kWh for gas (Direct Debit, GB average) for July–September 2026 — and is refreshed each quarter when the cap changes. Our price cap explainer covers how those rates are set.

The range rule: mid × 0.65 to mid × 1.55

A single average hides more than it reveals, so every cost is published with a typical range: the mid-point multiplied by 0.65 at the low end and 1.55 at the high end. The asymmetry is deliberate — real quotes overshoot the average more often, and by more, than they undershoot it (bigger properties, awkward access, higher-spec kit). A heat pump with a £11,014 mid-point therefore shows as £7,159–£17,072.

The regional index

Multiply the national mid-point by the index to get our regional figure. Rounded to the nearest pound, this is the entire regional calculation — no other adjustment is applied.

Savings and payback

Modelled annual savings (for example, up to £577 for solar and £452 for a heat pump) are estimates for a typical household at current cap rates, and we always write them as “could save up to”. Simple payback is the modelled mid-point cost divided by the modelled annual saving, rounded to the nearest year. It ignores price inflation, financing, maintenance and grant support unless stated — where a grant applies, as with the £7,500 Boiler Upgrade Scheme, we show payback both ways.

Limitations — read these before quoting us

• These are modelled desk-research estimates, not quotes, surveys of completed installations, or installer billing data.
• Your property can move a real quote far outside our range: listed status, roof condition, system size, access and spec all matter more than region.
• Regional indices are averages — a rural Highlands job and a central Edinburgh job carry the same Scotland multiplier.
• Savings depend on usage, occupancy and tariff; a household on a time-of-use tariff will see different numbers from the cap-rate defaults.
• Official statistics can differ from our model for structural reasons — DESNZ’s median for grant-funded heat pump installations (£13,041 in 2025/26) runs above our all-comers average, because grant-funded jobs skew complex.
• Figures are dated July 2026 and revised when the Ofgem cap changes; always check the date on any page citing the index.

If you spot an error or a figure that has drifted from reality, we want to know — the index only earns trust by being checkable. Start comparing costs on the Cost Index, or put your own numbers into the savings calculator.