This heat pump running cost calculator estimates electricity charges for a chosen period. Use measured heat-pump electricity consumption if you have it. For a proposed hydronic system, use the installer’s annual electricity estimate or work through the estimate below.
Enter the unit rate from your own electricity tariff. No current tariff rate is built into this calculator because rates and time-of-use periods vary.
1. Calculate the cost from electricity use
This is the simplest method for an installed heat pump. Use electricity measured for the heat-pump system over the same period you want to cost. Check what the meter or monitoring system includes, such as space heating, hot water, pumps and immersion or backup heating.
- Heat-pump electricity used: __________ kWh
- Period covered: ____________________
- Electricity unit rate: __________ p/kWh
Electricity cost (£) = electricity used (kWh) × unit rate (p/kWh) ÷ 100
For example, 4,000 kWh used at an assumed rate of 25p/kWh would cost £1,000. This is an arithmetic example only, not a current tariff quote or a typical heat-pump cost.
If your tariff has different rates, calculate each period separately and add the costs:
Cost (£) = [(kWh at rate 1 × rate 1 in p/kWh) + (kWh at rate 2 × rate 2 in p/kWh)] ÷ 100
Repeat the calculation for any additional rate periods. Use the heat pump’s kWh in each period, not the whole household’s total unless that is all the data available. For a simple annual estimate, annual cost ÷ 12 gives an average month, not a prediction of each month’s bill.
2. Estimate electricity use for a proposed hydronic heat pump
For a proposed air-to-water or ground-source hydronic system, use the total annual electricity consumption from the installer’s performance estimate if available. The MCS 031a hydronic heat-pump standard estimates electricity for space heating, hot water and immersion heating. If the estimate gives a total, use that figure directly and do not add its components again.
If you are building a manual estimate, use annual heat demand in kWh/year and a seasonal performance factor from the system design. Do not enter the heat pump’s rated capacity in kW or a room-by-room heat-loss figure in kW. Those are different measurements.
Estimated space-heating electricity (kWh/year) = annual space-heating demand (kWh/year) ÷ seasonal performance factor (SPF)
Use the installer’s system-specific SPF where possible. A single-point CoP from a product data sheet is measured under test conditions and should not be treated as the system’s annual performance. The Energy Saving Trust’s heat-pump guide explains the difference.
Add hot water and immersion electricity where needed
The space-heating formula does not include hot water or immersion heating. For a manual hydronic-system estimate, the MCS 031a method uses these additional calculations:
- Hot-water electricity: annual hot-water demand (kWh/year) ÷ 1.9. The MCS standard specifies 2.2 for hot water heated only by a ground-source heat pump.
- Immersion electricity: F × cylinder volume in litres × 10 × 4,200 ÷ 3,600,000 = kWh/year. Use the pasteurisation frequency and cylinder volume specified for the system estimate. The MCS method’s factor of 10 represents a 10°C temperature rise.
For an existing system, use measured electricity consumption if available. For a proposed system, ask the installer for the complete annual electricity estimate, including hot water and any immersion or backup use. Do not change hot-water hygiene settings based on this cost calculation; follow the system instructions and installer’s advice.
Total estimated electricity (kWh/year) = space-heating electricity + hot-water electricity + immersion electricity
The MCS 031a estimate presents a low and high range around its total. If your installer’s report supplies that range, calculate the cost for both figures using your tariff.
3. Worked space-heating example
Assumed inputs for illustration only: annual space-heating demand of 12,000 kWh, an SPF of 3.0 and an electricity rate of 25p/kWh.
- 12,000 kWh ÷ 3.0 = 4,000 kWh of estimated space-heating electricity.
- 4,000 kWh × 25p ÷ 100 = £1,000 for space-heating electricity over the year.
- £1,000 ÷ 12 = £83.33 average per month.
This example excludes hot water, immersion heating and other system electricity. Add them before calculating the full system cost. The example rate is an assumed input, not a tariff quote or a typical price.
4. Record your result
- Method used: measured electricity / installer estimate / manual estimate
- System and components included: __________________________________
- Electricity used: __________ kWh for ____________________
- Unit rate or rate periods: __________________________________________
- Estimated electricity cost: £__________
- Annual average per month, if calculated: £__________
What this calculator includes and excludes
- This is an estimate of electricity charges for the heat pump and any components included in the kWh figure you entered.
- It does not include the household electricity standing charge, servicing, repairs, finance or the cost of another heating fuel in a hybrid system.
- It does not show whether a heat pump will cost less than the system it replaces. That comparison depends on the previous system, its fuel, its efficiency and the tariffs used.
- If your system uses electricity from solar panels or a battery, this calculation applies the rate you enter to all the kWh. It does not value self-generated electricity separately.
For more help understanding household electricity data, see UK Prepared’s guide to measuring and reducing electricity use at home.
Further heat-pump cost and performance resources
- The MCS 031a standard sets out a method for estimating annual electricity use for hydronic heat-pump systems.
- The Energy Saving Trust heat-pump guide explains seasonal performance and how it differs from a single CoP figure.
- Energy Saving Trust’s heat-pump questions covers tariffs and why costs depend on the system being replaced.
- Energy Saving Trust’s guide to running a heat pump efficiently covers controls, operating patterns and time-of-use tariffs.
- UK Prepared’s guide to measuring electricity use at home explains meter readings and ways to investigate household consumption.
