Heat Pump vs Conventional Heating Cost Calculator

About the Heat Pump vs Conventional Heating Cost Calculator

A heat pump moves heat instead of making it: for each unit of electricity it delivers about three units of heat or more, where an electric geyser or heater delivers one and a gas, LPG or oil boiler less than one unit of heat for each unit of fuel. Whether it is cheaper depends on what you pay for electricity and for the fuel, how much heat your home needs, and what each option costs to buy, fit and keep.

This calculator works it out for hot water (a heat pump water heater against an electric geyser, a gas or LPG geyser, a solar water heater), for space heating (an air or ground source heat pump against a gas, oil or LPG boiler, electric heaters or wood pellets), or both. The heat comes from your litres of hot water or from a year of your current fuel; each option’s energy is that heat ÷ its seasonal efficiency, in its own units (kWh, therms, cubic metres, cylinders, litres), with its running cost and CO2. The comparison shows a year of each at today’s prices, in full.

The lifetime report adds the cost to buy and fit less any grant, price rises, maintenance, replacements and the value left at the end, in today’s money: the cheapest option over your years, the payback, the electricity price at which a heat pump stops paying, the cost of a kWh of heat, the CO2 saved and what happens if prices or efficiency change, with a PDF report and a CSV. Without a pass you see the yearly comparison in full and a free preview of the report; every figure of the report and the downloads come with a Pro pass. Nothing you enter leaves your browser.

Common uses

• Deciding between a heat pump water heater, an electric geyser, an LPG geyser and a solar water heater.
• Seeing whether an air source heat pump costs less than a new gas or oil boiler over 15 years, with the grant.
• Finding the electricity price at which a heat pump stops paying, before switching tariffs.
• Comparing the CO2 of each option for a home or a small business.

How it is worked out

• Heat for hot water (kWh) = litres a day × (hot − cold °C) × 4.186 ÷ 3,600 × days a year: 4.186 kJ warms one kilogram of water by one degree, and a litre of water is about a kilogram.
• Heat for rooms = the heat a year you enter, or today’s fuel a year × its energy content × today’s seasonal efficiency (less the hot water when the same fuel heats it).
• Energy of an option = heat ÷ its seasonal efficiency; for a heat pump that is its seasonal COP (SCOP) or, for a water heater, its UEF; for a solar water heater its SUEF, which counts the backup electricity.
• Running cost a year = energy × price + a gas standing charge where leaving gas would save it + maintenance.
• Over the years: cost to buy and fit − grant + each year’s energy (with the price rise) and upkeep + a replacement when its life ends − the value left at the end, each year discounted to today’s money (net present cost). The payback is when its running total falls to the option you compare with; the break-even electricity price is the price at which both cost the same over the years.

Energy contents and CO2

Fuel energy is counted at the gross calorific value, the basis of UK and US appliance efficiencies. In metric units it comes from the UK government’s greenhouse gas conversion factors (the CO2 of a unit divided by the CO2 of a kWh): 13.70 kWh in a kg of LPG, 11.11 in a cubic metre of natural gas, 10.29 in a litre of heating oil, 4.80 in a kg of wood pellets. In US units it comes from the EIA’s Btu factors: a therm is 100,000 Btu (29.31 kWh), a cubic foot of natural gas 1,036 Btu, a gallon of propane 91,452 Btu and of heating oil 138,500 Btu. Fuel CO2 is from the same UK factors, or the US EPA emission factors for US visitors; the grid’s CO2 is your country’s figure, which you can change.

Efficiency figures to use

Use the seasonal figure from the datasheet, not a peak COP at mild weather. For reference: ENERGY STAR heat pump water heaters have a UEF of at least 3.30 and solar water heaters with electric backup an SUEF of at least 3.00; the US minimum for a 50-gallon electric storage water heater is about 0.92 and for an instantaneous gas water heater 0.81 (10 CFR 430.32). Heat pumps under the UK’s Boiler Upgrade Scheme need a SCOP of at least 2.8 (Ofgem). A heat pump does best with low flow temperatures and a home that keeps its heat; a heat-loss survey sizes it.

Grants and prices

In England and Wales the Boiler Upgrade Scheme pays towards an air or ground source heat pump; the calculator shows the current amounts and uses them in the UK sample. The UK energy price cap’s average rates are from Ofgem, and the US averages from the EIA. In the US, the federal Energy Efficient Home Improvement Credit covered heat pumps installed through 2025: enter a state or utility rebate as a grant instead. Prices change: use your own bills.

Sources

• UK government: greenhouse gas reporting conversion factors
• US EIA: British thermal units (Btu)
• US EPA GHG Emission Factors Hub
• ENERGY STAR: water heater key product criteria
• eCFR: 10 CFR 430.32 — water heater standards
• GOV.UK: Boiler Upgrade Scheme and Ofgem: the scheme’s rules
• Ofgem: energy price cap rates

Limitations

• An estimate to compare, not financial advice: real efficiency depends on the installation, the flow temperature and the weather, and prices change.
• It compares heating and hot water only; a heat pump that also cools replaces an air conditioner, which you can enter as a cost avoided.
• One price a unit for each fuel: tiered or time-of-use tariffs need their average price for the heating hours.
• Get a heat-loss survey and installers’ quotes before you decide; the costs here are what you enter.

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