A new build can have a small space-heating demand, but that does not make its heat pump bill negligible. Hot water remains an important load, and the efficiency of the two services can differ. A useful estimate separates those demands before applying an electricity tariff.
Use the building assessment carefully
The latest government EPC release reports that 89% of new domestic properties in England received A or B ratings in April - June 2026. The new-dwelling category includes conversions and changes of use, so this is not solely a statistic about newly constructed detached homes. Read the EPC release.
An efficient rating provides context, not your personal bill. Obtain the heating-demand assumptions and consider the indoor temperatures, occupancy and ventilation operation behind them. Your household may use the property differently from the assessment’s standard assumptions.
Calculate space heating and hot water separately
Consider an illustrative home requiring 6,000kWh of useful space heat and 2,000kWh of useful hot water heat annually. At seasonal efficiencies of 4 and 2.5 respectively, electricity use is 1,500kWh plus 800kWh: 2,300kWh in total. These are example inputs, not measured new build averages.
Ofgem’s October - December 2026 average Direct Debit electricity rate is 26.32p/kWh. Holding that rate constant gives an illustrative heating electricity cost of £605.36 per year. This excludes household appliances, standing charges, servicing and any electricity outside the stated efficiency boundaries. It is not a forecast of future tariffs. Check the dated Ofgem announcement.
Why hot water matters in an efficient home
As insulation reduces space-heating demand, showers and baths can represent a larger share of the heating total. Producing hotter stored water generally requires a different operating condition from supplying low-temperature underfloor heating.
Ask how cylinder reheating, storage losses and any immersion-heater operation enter the estimate. A single space-heating efficiency figure applied to every kilowatt-hour can make a low-demand home’s forecast look better than the full system is likely to achieve.
Test the estimate against less favourable assumptions
Keep the same useful demands but use space-heating efficiency 3 and hot water efficiency 2. Electricity then totals 3,000kWh, costing £789.60 at the example rate. That is £184.24 more than the first calculation.
This sensitivity test shows why commissioning and operating temperatures matter. It does not predict a fault or establish an acceptable performance threshold. Ask which efficiency values the designer considers realistic and how they will be checked after occupation.
Treat solar electricity as a timed resource
Solar panels may reduce purchased electricity when generation and heat pump operation overlap. Annual solar production cannot simply be subtracted from annual heating use: much heating demand occurs when daylight and generation are limited.
Cylinder scheduling may help use daytime generation where comfort and safety requirements permit. Compare import and export tariff terms before assigning financial savings. Batteries also have capacity, losses and investment costs that belong in their own appraisal.
Monitor the home after occupation
Record electricity consumption and useful heat where appropriate metering is available. Note occupancy, temperatures and weather when comparing periods. Whole-house electricity alone cannot distinguish heat pump consumption from cooking, appliances or vehicle charging.
For a new build in Horsham, ask Air Source Heat Pumps West Sussex for commissioning records and clear guidance on controls. Investigate persistent differences against the design assumptions with that evidence, rather than changing several settings and losing a useful baseline.
Build a household budget around separate costs
Heating electricity is only part of the household account. Cooking, lighting, appliances and vehicle charging can contribute substantially, so a whole-house bill is not a direct test of the heating forecast. Keep their expected consumption separate in the budget.
Set aside servicing and any finance payments as distinct costs. This helps you understand whether a change in the monthly total came from energy use, tariffs or contractual payments. If you compare two designs, use consistent demand and tariff assumptions and state how each treats auxiliary electricity. A comparison is more useful when you can trace the difference to a specific input.
Review performance over a suitable period
An initial month may include commissioning adjustments, unusual occupancy or construction drying. Record the circumstances before treating it as representative of a normal year. Short mild periods also do not establish performance during the colder season.
Compare the results with the design under similar conditions and seek advice when differences persist. Useful monitoring should support comfortable, safe operation. It should not encourage occupants to suppress necessary hot water reheating or abandon the intended ventilation strategy merely to improve a headline consumption figure.
Summary
New build running costs depend on both low-temperature space heating and hotter domestic water. Use separate demand and efficiency assumptions, test their sensitivity and monitor the completed home. Our new build heat pump service can help explain the design behind the estimate.
