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Heat pump or gas boiler: comparing running costs

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Compare the same useful heat for the house and hot water. The boiler needs gas according to seasonal efficiency, while the heat pump needs electricity according to its seasonal factor. Fixed charges and retaining a gas connection can change the result.

A lower annual energy cost is not a payback calculation for the complete investment.

Fuel consumed and useful heat

For the boiler, billed gas energy = useful heat ÷ seasonal efficiency on the same calorific-value basis. Nominal laboratory efficiency may not describe annual operation including hot water.

For the heat pump, use a factor matching the selected system boundary. If gas remains for cooking or backup, its fixed charges may remain too. The calculator assigns the same gas fixed charge to the boiler and a heat pump with a retained connection.

Compare annual costs using your inputs

Calculations run in your browser. Enter your own data; an empty field does not mean zero. You can use a decimal point or comma and spaces between thousands.

Heat demand

Heat demand after accounting for the old heat source’s efficiency, rather than energy taken directly from a bill.

Separate demand. Enter zero only if hot water is excluded from the comparison.

For example, a design after insulation, a measurement period or your own illustrative scenario. State which consumption the factor includes.

Consumption calculation method

Catalogue SCOP is not automatically this factor. It must include space heating, any hot water included, backup and auxiliaries.

Your electricity tariff

Use final rates including applicable distribution charges and VAT. Off-peak hours are not the share of energy used off-peak. Enter only the increase in fixed charges compared with your current situation.

Gas: the same useful heat

Use prices and efficiency on the same billed-energy basis. The gas tariff band must match the modelled consumption; include VAT and network charges.

Investment, service and lifetime

An investment decision includes equipment, installation, distribution and radiator upgrades, electrical work, servicing, financing and replacements. These costs are not silently included in the annual energy calculator.

Simple payback requires a positive net annual saving and a correctly defined additional investment. It has no finite value with zero or negative savings. A longer-term comparison needs equipment lifetimes, repairs and future-price assumptions.

When the result shows no saving

A low seasonal factor, substantial resistance heating, an unsuitable tariff, higher fixed electricity charges or retained gas can make the result unfavourable. Review the design and assumptions rather than replacing them with a more attractive label figure.

Sensitivity calculations vary one group of assumptions at a time. They are not a price forecast or a guaranteed range for your bill.

Common questions

Will I save the gas subscription if I keep gas for cooking? Use your contract; connection charges generally remain. Select retained gas in the calculator.

Can I compare billed kWh directly? First convert to the same useful heat. Electricity and gas have different conversion and system losses.

Sources

We are an independent information site. We do not sell or install equipment. These dated sources do not replace a design for your home. Source links are not affiliate links.