The building work, the heating and the panels planned as one job
OKPW builds extensions in south west London and plans a heat pump and solar panels into the same job. We do the building work and coordinate the programme. The heat pump or solar system is installed and certified by an MCS-certified installer. OKPW has traded since 2007.
The work splits into two parts. It helps to know who does which before you compare quotes.
The Boiler Upgrade Scheme grant is towards the heat pump, not the building work.
Fitting a heat pump after the building work is finished means lifting floors and chasing walls again. Solar panels need scaffolding. During an extension, most of that is happening anyway.
The pipes between the outdoor unit, the cylinder and the heating run under floors and through walls. During a build those are open already. Later it means lifting finished floors and chasing finished walls, then plastering and decorating again.
A heat pump needs a hot water cylinder. Most three and four bedroom homes need a 200 to 250 litre cylinder, which takes roughly 600mm by 800mm of floor. That space is easy to draw into a new layout and hard to find afterwards.
Underfloor heating sits in the floor build-up: insulation, then pipes, then screed. In a new extension the floor levels are set out for that depth from the start. Underfloor heating works at low water temperatures, which suits a heat pump.
A heat pump runs at 30 to 45°C, cooler than a boiler, so some radiators need to be bigger. It is simpler to change them while the rooms are being worked on anyway.
Solar panels need safe access to the roof, and the roof structure has to be checked before panels go on. Where the build already has scaffolding at roof level, or roof work under way, that is the time to do both.
A heat pump, solar panels and a battery all connect to the consumer unit and the electricity supply. An extension needs electrical work anyway, so the capacity is checked once for everything. The network operator has to be told about a heat pump and about solar panels.
To be fair about it: if all you want is a boiler swapped for a heat pump, with no building work, a specialist installer on their own may well be quicker and cheaper.
These are decided on the drawings, before work starts:
In England a heat pump is normally permitted development, within limits on the size and position of the outdoor unit. A listed building needs consent, and a conservation area restricts where the unit can go. Solar panels are normally permitted development within limits too.
For the extension itself, we check permitted development for free. Where full planning is needed, we prepare and submit the application. Our guide to planning permission for extensions sets out the rules.
The building work and the systems are priced on separate lines. These are guide prices, not quotes. Your exact price follows the free survey.
| Building work | Sizes the guide covers | Guide price, plus VAT |
|---|---|---|
| Rear extension | Smallest: 3m depth (about 12m²) Largest: 6m+ depth (about 30m²+) | £62,000 to £165,000 plus VAT |
| Side return extension | Smallest: 1-2m width (about 6-10m²) Largest: 3m+ width (about 20m²+) | £40,000 to £120,000 plus VAT |
| Wraparound extension | Smallest: up to 20m² Largest: 30m²+ | £120,000 to £200,000 plus VAT |
| Double storey extension | Smallest: 3m depth (about 24m² total) Largest: 6m+ depth (about 50m²+ total) | £100,000 to £260,000 plus VAT |
These guide prices are illustrative while launch pricing is finalised. They are the same figures our cost calculator uses. The guide prices for a rear extension and a wraparound extension include underfloor heating in the new floor. All four include project management.
The building work prices leave out:
The systems are priced apart from the building work. The heat pump price is shown before any grant. These are illustrative guide prices, not quotes.
| System | Who fits it | Guide price |
|---|---|---|
| Air source heat pump | Installed and certified by an MCS-certified installer. Typically 3 to 5 days on site. | from £11,500 before any grant |
| Solar panels and battery | Installed and certified by an MCS-certified installer. Typically 1 to 2 days on site. The network operator is notified or applied to as well. | from £11,150 the grant does not cover solar |
Boiler Upgrade Scheme grant: £7,500 towards an air-to-water or ground source heat pump. It is shown on its own line because it is not part of any price above. Under the scheme’s rules the MCS-certified installer applies for it. It does not cover solar panels or batteries. Checked 10 November 2026.
0% VAT currently applies to qualifying energy-saving installations. That rate is for the heat pump and solar lines only. The building work prices are plus VAT at 20%.
The Boiler Upgrade Scheme is a grant towards the cost of a heat pump. These are its main rules:
The scheme gives nothing towards solar panels or batteries.
Grant amounts and the energy certificate rule checked on 10 November 2026. This is a guide to the rules, not a decision on an application. Our guide to heat pump costs and grants has more.
We have not yet published a heat pump or solar project. The closest finished job on our site is an extension with underfloor heating.
Wrap-around extension & full refurbishment, London SW12
A wrap-around extension, rear and side return together, to a ground-floor flat. One floor is laid wall to wall, with underfloor heating across it. The heating is fed by a boiler, not a heat pump. Built to an architect’s drawings, 115m² gross internal area, completed in 2025.
See the Dornton Road projectRead the Dornton Road case study
For the systems on their own, see heat pumps, solar and battery, underfloor heating and our renewables page. Our guide asks whether solar panels are worth it. If you have no drawings yet, see design and build.
Yes. OKPW builds the extension and plans the heat pump and solar panels into the same programme. We do the building work and coordinate the job. The heat pump or solar system is installed and certified by an MCS-certified installer.
An MCS-certified installer fits and certifies them. OKPW does the building work and coordinates the programme. We do not name the installer on this page. Ask us at the survey which firm would fit and certify your system.
The Boiler Upgrade Scheme gives £7,500 towards an air-to-water or ground source heat pump. It does not cover solar panels or batteries. Under the scheme’s rules the MCS-certified installer applies, not the homeowner or the builder. Checked 10 November 2026.
No. The grant is towards the heat pump, not the building work. Under the scheme’s rules the full grant comes off the installer’s price before you pay.
The building work and the systems are priced separately. Our guide price for a rear extension is £62,000 to £165,000, plus VAT. An air source heat pump is from £11,500 before any grant. Solar panels with a battery are from £11,150, and the grant does not cover them. These are illustrative guide prices while launch pricing is finalised, not quotes. 0% VAT currently applies to qualifying energy-saving installations. Your exact price follows the free survey.
Often not. In England a heat pump is normally permitted development, within limits on the size and position of the outdoor unit. A listed building needs consent, and a conservation area restricts where the unit can go. Solar panels are normally permitted development within limits too. The extension itself may need planning permission, and we check that for free.
A heat pump is typically fitted in 3 to 5 days and solar panels in 1 to 2 days, inside the extension programme. Most single-storey extensions take 3 to 6 months on site, plus 8 to 12 weeks beforehand if a planning application is needed.
Send us a few lines about the house, the extension you have in mind and the systems you are thinking about. We will be in touch to arrange a free survey.
Central, South and West London and Surrey, out to Guildford and Dorking. See our work by borough
+44 (0) 773 776 6859
+44 (0) 791 235 7492
