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Heat pump running-cost calculator

Start with the heating system and fuel you already use. Wattlas estimates useful annual heat from that, then compares it with a heat pump on your electricity tariff.

This is an annual running-cost comparison, not a heat-loss survey or a system-size recommendation.

Your home and current heating

Choose the system that supplied the heating and hot water included in the annual figure below.

Use the last 12 months from bills, oil deliveries or your meter. For direct electric heat, enter the heating share only.

This sets a cautious seasonal-efficiency estimate; it is not the boiler’s marketing rating.

Untick only when the annual figure is space heating alone or hot water is supplied separately.

Uses the MCS starting point of 45 litres per person per day.

Proposed heat pump and tariff

Use the seasonal performance figure from the proposal. A higher SCOP uses less electricity for the same heat.

Hot water usually needs a higher temperature than space heating, so use a lower figure than the space-heating SCOP unless your proposal says otherwise.

Choose a cheap period only if you expect the cylinder to be scheduled there. Space heating remains separately modelled.

Optional installation cost

How the estimate works

Wattlas converts the fuel use you enter into energy, removes any gas you identify as cooking use, then applies a cautious seasonal efficiency for the selected system and age. That estimates useful heat. The heat pump needs that useful heat divided by SCOP in electricity. The monthly chart uses a typical UK heating-season shape; it is not a heat-loss survey or weather forecast.

Common questions

What SCOP should I use?

Use the proposal's seasonal performance figure for your property and design temperature. Do not use a short-term peak efficiency figure. There is no reliable universal size-to-SCOP table: size is chosen from the home's design heat loss, while SCOP changes with the specific model, outdoor conditions and flow temperature. The Energy Saving Trust's manufacturer-data examples show why a 35°C flow temperature can perform materially better than 55°C. Check the proposal's model-specific MCS/installer calculation.

Can I use this for a gas, oil, LPG or electric system?

Yes. Select the closest listed source. For gas, oil and LPG boilers the age selection changes the seasonal-efficiency estimate; direct electric systems are treated as resistance heat. Enter the annual fuel use rather than a quote's predicted running cost.

Why is a heat-loss survey still important?

Annual running cost does not show whether the heat pump is correctly sized or whether radiators and pipework can deliver the required heat. A competent survey addresses those questions.

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