PC Project Cost Lab
UK works tools

GUIDE

Combi swap versus heat pump versus PV

Last checked September 2026 · Published by Rodway Labs

Not a quote. Figures in this guide are illustrative UK cost bands compiled for planning. They are not a tender, valuation or building-regulation ruling. Get written quotes for the property. Project Cost Lab (Rodway Labs) is not a contractor, architect or quantity surveyor. The mid figure is a band, not a price; the VAT toggle is a display choice, not a ruling.

Same cupboard word, different job

Search results often lump “boiler cost”, “heat pump cost” and “solar panel cost” together as energy upgrades. On site they are different packages: a like-for-like combi swap in the same cupboard is not an air-source heat pump with emitters and controls, and neither is a roof-mounted PV array priced per kilowatt-peak. This guide separates the bands used in Project Cost Lab.

Gas boilers — compiled mid illustrations

A like-for-like combi in the same location is the cheaper domestic plant job in 2026 trade guides: compiled mid about £2,800 before VAT display and contingency. Relocation, flue changes and system cleans are common add-ons.

A system / regular boiler sits higher — compiled mid about £3,800 — because cylinders, open-vented pipework or heating-zone changes get involved. “Boiler” on an invoice can therefore mean either band.

Air-source heat pumps

An air-source heat pump for a typical house is a different order of work: outdoor unit, indoor cylinder or thermal store, controls, and often emitter upgrades if radiators were sized for hotter flow temperatures. This lab’s compiled mid is about £13,000 before grants and before your VAT display choice.

Grants and schemes sit outside the range. Do not net a government grant off inside this tool — treat support as a separate cash-flow item confirmed against current scheme rules. Fabric first (insulation, draughts) still affects whether a heat pump quote looks sensible.

Solar PV and batteries

Solar PV in this lab is priced per kWp (default 4 kWp, compiled mid about £1,650 / kWp before factors). Scaffolding, inverter type, roof covering and export arrangements change real quotes.

A battery is a separate line, typically per kWh of storage. Adding PV and a battery on the same day as a heat pump is three packages, not one “green” number.

VAT display on energy kit

Some energy-saving measures can attract reduced or zero VAT in UK rules, depending on the measure and the customer. That is why the calculator lets you show 20%, 5%, 0% or ex-VAT — as a display choice, not a determination. Confirm treatment with your installer and tax adviser. See the VAT on works guide.

How to compare quotes fairly

  1. Write down whether the job is like-for-like, relocation, full system or heat-pump retrofit.
  2. List emitters, cylinder, controls and electrical upgrades in or out.
  3. For PV, fix kWp, roof type and whether a battery is included.
  4. Ask each quote to state VAT treatment explicitly.
  5. Use this site only to size a planning band before those quotes arrive.

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Related: Region & access · VAT on works