Heat Pump Design

Heat Pump Cost & Heat Loss

Compare running costs, explore seasonal performance and estimate whole-building heat loss. Planning estimates with editable assumptions.

Read the worked examples and planning guide →

Adjust your comparison

Set useful heat and SCOP, then choose a fuel and tariff. The results compare the same delivered heat.

Enter heat delivered to your rooms and hot water after boiler losses. Purchased gas kWh × your boiler efficiency gives useful heat. The initial 12,000 kWh is an example, not your building estimate.
Seasonal Coefficient of Performance: useful heat divided by all relevant heat-pump electricity over the year. Include hot water and auxiliaries consistently. SCOP 3 means 3 kWh of heat for each kWh of electricity.

Condensing boilers recover heat from exhaust vapour. Choose your boiler type to set an editable starting assumption. Age, return temperature, cycling and controls affect actual fuel use. These examples are not measured ratings.
Of every 100 kWh of fuel energy, this percentage becomes useful heat over the year. At 90%, 10% is lost. Use an annual gross/HHV efficiency for your installation, including hot-water operation if included. A flue-gas combustion reading or a laboratory rating may overstate annual performance. You can adjust this example from 50–98%.
Condensing boilers recover heat from exhaust vapour. Choose your boiler type to set an editable starting assumption. Age, return temperature, cycling and controls affect actual fuel use. These examples are not measured ratings.
Of every 100 kWh of fuel energy, this percentage becomes useful heat over the year. At 90%, 10% is lost. Use an annual gross/HHV efficiency for your installation, including hot-water operation if included. A flue-gas combustion reading or a laboratory rating may overstate annual performance. You can adjust this example from 50–98%.
Condensing boilers recover heat from exhaust vapour. Choose your boiler type to set an editable starting assumption. Age, return temperature, cycling and controls affect actual fuel use. These examples are not measured ratings.
Of every 100 kWh of fuel energy, this percentage becomes useful heat over the year. At 90%, 10% is lost. Use an annual gross/HHV efficiency for your installation, including hot-water operation if included. A flue-gas combustion reading or a laboratory rating may overstate annual performance. You can adjust this example from 50–98%.
Use an all-day electricity price or your delivered battery price. Time-of-use structures below require quoted band rates and shares of electricity used in each band. The cheapest band alone does not establish an annual bill.
Price for purchased mains gas energy, before boiler losses. Replace this dated national average with your VAT-inclusive bill rate.
Use your delivered, VAT-inclusive kerosene price per litre. Divide by the fuel energy content before applying the separate oil boiler operating efficiency.
The editable 10.35 kWh/litre is a gross-energy planning assumption. Match the oil boiler efficiency to this same gross/HHV basis; do not copy a net/LHV efficiency unchanged.
70p/litre is an illustrative input, not a verified current bulk offer. Enter your own VAT-inclusive delivered propane quote. Tank rental and standing charges are excluded.
£112 is a London Gases regional 47kg propane refill example checked 1 November 2026, not a UK average. Enter your local refill quote including VAT and delivery. Cylinder deposits and equipment costs are excluded. Partial cylinders shown in results represent annual fuel use, not a purchase order.
The propane assumptions are 7.08 kWh/litre and 14.019 kWh/kg, using a gross/HHV planning basis. Supplier fuel composition and temperature can vary. Use matching gross boiler efficiency; do not mix in net/LHV ratings.
47kg × this energy content gives purchased energy in a refill. Gross/HHV includes heat recoverable by condensing water vapour; net/LHV excludes it. Never combine a net efficiency with gross fuel energy.
For an additional fuel, enter cost per useful kWh after its own losses. Leave blank to omit the optional row.

Useful heat is heat delivered after boiler losses: 12,000 purchased gas kWh × 90% = 10,800 useful kWh. The 12,000 kWh starting value above is illustrative and independent of the heat-loss estimate below.

SCOP is whole-system seasonal performance for all included heat, including hot water and relevant auxiliaries. A SCOP of 3 delivers 3 kWh of heat per kWh of electricity.

Direct electric tariff

Use the rates available to the direct electric system. For a flat tariff, enter the rate under Standard and leave off-peak use at 0%.

Use the share of electricity consumed. The rest is charged at the standard rate. The comparison assumes resistance heating and excludes storage losses.

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Energy costs only: excludes capital cost, maintenance and standing charges. A gas standing charge is avoided only if the gas supply can actually be removed. Time-of-use prices need a consumption profile; the cheapest window alone is not an annual cost.

Price sources and calculation assumptions

Snapshot checked 1 November 2026: electricity 26.32p/kWh and gas 7.97p/kWh are Ofgem average Direct Debit rates for 1 October–31 December 2026. Oil 116.80p/litre including VAT is the BoilerJuice UK indicative 1,000-litre average for 1 November. Regional prices, payment method and delivered quotes vary. This is not a live price feed.

Heat-pump electricity = useful heat ÷ SCOP. Boiler fuel = useful heat ÷ operating efficiency. All boiler efficiencies here use a gross / higher-heating-value (HHV) planning basis, capped below 100%; do not enter a net/LHV rating unchanged. Oil litres = purchased oil kWh ÷ the editable 10.35 kWh/litre planning assumption (heating-oil reference). Confirm the fuel’s gross energy content and the boiler’s gross operating efficiency with the supplier. Custom fuel is priced per useful kWh, after any fuel-system losses.

LPG means propane here. Bulk fuel uses p/litre ÷ kWh/litre. A bottled refill uses £ per 47kg ÷ (47 × kWh/kg). Both then apply the separate LPG boiler efficiency. Editable propane assumptions are 7.08 kWh/litre and 14.019 kWh/kg, informed by Flogas fuel conversions on a gross/HHV planning basis; that FAQ does not explicitly label HHV/LHV, so confirm your supplied fuel basis. The 70p/litre bulk input is illustrative: Calor requires a quote. The £112 bottled example is a London Gases 47kg refill including VAT, checked 1 November 2026 for its regional delivery area; it is not a national price. Obtain a local delivered quote and allow separately for tank rental, cylinder deposits and equipment.

Condensing/non-condensing selections set editable operating examples (gas/LPG 90% or 75%; oil 85% or 75%). They are planning assumptions, not ratings for every boiler. Energy Saving Trust explains boiler types; use the actual model and installation evidence to refine annual performance.

Break-even SCOP = electricity p/kWh × boiler efficiency ÷ fuel p/kWh. Percentage difference uses the selected comparator’s cost. Free fuel or zero demand makes the percentage unavailable. Seasonal performance requires system design and operating evidence; it cannot be inferred from flow temperature alone.

Compare daily battery shifting with outage capacity · Continue to the building heat-loss estimate

Screening estimate only. Total floor area includes every storey; exposed element areas are entered separately. The result excludes hot-water recovery and any plant-sizing uplift.

Example home: 150m² over two floors

This illustrative insulated home gives about 4.73kW space-heating loss at 21°C indoors and −1°C outdoors. Change the inputs for your building.

View example geometry and assumptions

A detached 10m × 7.5m rectangle, two 2.5m storeys: 75m² footprint, 375m³ heated volume and 175m² gross external wall. Subtract 25m² windows and 3m² doors to give 147m² net wall. The 75m² roof boundary is the insulated ceiling below an unheated loft.

Insulated cavity walls, insulated ground floor and modern double glazing are illustrative starting values, not surveyed construction. Thermal bridges, detailed ground transfer and boundary corrections need a full room-by-room design.

Property Details

Add the heated area of every storey. The example has two 75m² floors = 150m². Do not multiply this total by the storey count again.
Average height within the heated envelope. Total floor area × average height gives the volume used for ventilation loss.

Temperature Settings

Winter design outdoor temperature for the location, not the annual average or a record minimum. The example −1°C is editable and is not a postcode assessment. Use the design temperature for the actual location.
Design indoor temperature. Heat loss is proportional to the difference between this and the outdoor temperature. Individual rooms may need different design temperatures.
Annual weather demand at a stated base temperature. The example 2,100 K·days uses base 15.5°C and no selected postcode. It affects only the annual space-heat estimate; replace it with local data.Illustrative UK value at base 15.5°C; replace with local evidence.

Building elements — exposed areas net of openings

WALLS

An illustrative U-value preset. Selecting a type updates only the wall U-value; then replace it with surveyed construction evidence if available.
Heat passing through each square metre per degree of temperature difference. Lower is better insulation. Use the whole wall build-up, not just an insulation layer.
Only exposed external wall, net of windows and doors. Example: perimeter35m × total wall height5m −25m² windows −3m² doors =147m². Exclude internal walls.

ROOF & FLOOR

Choose the construction at the heated boundary. An unheated loft normally has its boundary at the ceiling; a heated loft may use sloping roof area instead.
U-value of the ceiling or roof boundary enclosing the heated space. The example 0.16 W/m²K is illustrative insulation, not a guarantee for every pitched roof.
Area of the boundary losing heat. The example uses the horizontal 75m² ceiling below an unheated loft, not the area of the pitched roof covering.
Illustrative construction preset for the exposed ground or suspended floor. It changes its U-value only; detailed ground heat transfer requires a separate assessment.
Effective exposed-floor U-value. A surveyed calculation should account for floor construction, perimeter/area and ground conditions. The example uses 0.25 W/m²K.
Only floor losing heat outside the heated envelope. The example has a 75m² ground floor. The upstairs floor between heated rooms is not an external heat-loss surface.

Windows & Doors

Illustrative whole-window U-value preset, including the frame. Modern double glazing varies; use the declared whole-window value when known.
Whole-window U-value including frame effects, not centre-pane glass U-value. The example is 1.4 W/m²K; all glazing areas use this same screening value.
Total exposed windows and glazed openings represented by the window U-value. Subtract the same openings from wall area so they are not counted twice.
Total external door area. Glazing counted as a window must not be counted again here or in net wall area.
Whole-door thermal transmittance. The example 2.5 W/m²K represents an older door assumption; enter product or construction evidence for your doors.

Ventilation & Air Tightness

Air changes per hour through the heated volume. For natural ventilation or extract fans, include all ventilation and leakage. With MVHR, enter mechanical airflow here and unrecovered leakage separately. The example 0.6 is illustrative, not a ventilation prescription. Natural ventilation: include leakage in ACH. With MVHR: enter mechanical ventilation ACH and add unrecovered leakage below.
Only MVHR receives heat-recovery credit. Natural ventilation and extract-only systems use the entered ACH without recovery; they still require adequate ventilation.
Uncontrolled leakage bypassing MVHR heat recovery. Use airtightness evidence where available; 0.15 ACH is an illustrative allowance, not a measured default for every house.Illustrative leakage allowance; assess airtightness separately. Heat recovery does not recover this loss.
Effective heat recovery for the mechanical ventilation flow only. It does not reduce fabric or leakage loss. Example 85% is an editable assumption; use system design and commissioning evidence.