How an estimate is worked out
Published standards for the heat loss, your own prices for the heat pump, and always a survey before the final quote.
It starts with the home's EPC
An Energy Performance Certificate is made when a home is sold, let or improved. An accredited assessor visits and records the home's details: its floor area, walls, roof, floors, windows and heating. Every certificate is kept on the government's public EPC register.
When a homeowner picks their address, the calculator reads that home's latest certificate from the register and fills in what it knows. The homeowner can check it and change anything that isn't right, such as insulation added since.
What the EPC gives us
- Floor area and number of floors
- Property type and when it was built
- Walls, roof and floor, and their insulation
- Windows and glazing
- Main heating and fuel
- The home's energy rating
No certificate for the home? Full width uses similar homes with certificates on the same postcode; Compact asks the homeowner a few quick questions.
The heat loss follows published standards
A heat pump is sized to the home's heat loss: how much heat it loses on a cold winter's day. In the Full width style, we work it out with the same methodology and data behind EPCs and heat pump design.
SAP 10.2 and RdSAP 10
The government's Standard Assessment Procedure, and its reduced-data version for existing homes. It's the same methodology used to produce Energy Performance Certificates, so the heat loss is worked out the same way the home's EPC was.
RdSAP 9.94 defaults
Older certificates don't list every window. For those, we use the default window areas the previous version of RdSAP sets out for homes of that type and age.
MCS MIS 3005-D design temperatures
The Heat Pump Design Standard's outside design temperature for the location nearest the home (the 99.6% figures, from CIBSE Guide A), against 21 °C inside.
Ofgem Boiler Upgrade Scheme guidance
In Full width, whether the home is likely to qualify for the grant, and how much, follows Ofgem's Property Owner Guidance: £7,500, or £9,000 where the off-gas uplift applies.
Full width runs the full heat loss calculation above, with the homeowner fine-tuning their home's details. Compact is the quick version: it sizes the heat pump from the home's type and number of bedrooms, filled in from the EPC where there is one. Compare the styles →
Your prices, matched to the home
You set your own installed price for each heat pump size you fit, from 4 kW to 24 kW, before the grant. Switch off the sizes you don't offer.
For each home, the calculator picks the smallest size you offer that covers its heat loss, takes off the grant it's likely to get, and shows the homeowner a range of 10% either side, rounded to the nearest £50.
If a home needs a bigger heat pump than any you offer, it shows no price and says you'll recommend the right system after a survey.
Heat loss for this home: 6.8 kW
| Size | Your price | Chosen |
|---|---|---|
| 5 kW | £9,500 | Too small |
| 6 kW | £10,000 | Too small |
| 7 kW | £10,500 | Smallest that covers 6.8 kW |
| 8 kW | £11,000 |
Always subject to a survey
The estimate is a guide to help homeowners budget, not a quotation. Before you quote, you confirm the right heat pump with a full room-by-room heat loss survey, as MCS requires, and you confirm grant eligibility when you apply. The calculator shows a disclaimer saying so, in your words.
“An estimate only. We'll confirm your price after a home survey.”