Heat pump running cost
heat_pump_running_costCompare what a household spends heating on its current fuel with what the same heat would cost from a heat pump.
The heat demand is worked out from the household's own metered fuel use, not from a model, because a year of bills describes a particular house far better than any estimate of it. Supply the annual fuel use in the fuel's own unit (kWh for gas and electricity, litres for oil and LPG, kilograms for coal), its price per unit in pounds, and the seasonal efficiency of the existing appliance, which defaults to a realistic figure for that fuel instead of the one on the badge.
The comparison turns on one ratio. A heat pump costs less to run whenever its seasonal coefficient of performance beats the ratio between the price of a unit of electricity and the price of a unit of heat from the current fuel. The result reports that break-even figure explicitly.
SCOP must be the figure at the flow temperature the system is actually designed for. The same machine can return 4.2 at 35 degrees and 3.1 at 55, and quoting the first for a system designed at the second is the commonest way of overstating a saving.
This is a running cost comparison. It says nothing about the capital cost or any grant.
Method from MCS 007. These calculators follow the published MCS methods, for understanding a system and checking a quotation. Anything that gets installed still needs a design and a site survey from a certified installer.
Input Schema
| Name | Required | Description | Default |
|---|---|---|---|
| fuel | No | The fuel being replaced: 'mains_gas', 'oil', 'lpg', 'electricity' or 'coal'. Defaults to 'mains_gas'. | |
| scop | Yes | Seasonal coefficient of performance of the proposed heat pump: the units of heat it delivers per unit of electricity, averaged over a year at the design flow temperature. Required. | |
| annualFuelUse | Yes | How much of that fuel the house uses in a year, in the fuel's own unit: kWh for gas and electricity, litres for oil and LPG, kilograms for coal. Take it from a year of bills. Required. | |
| fuelPricePerUnit | Yes | Price of one unit of that fuel, in pounds. Required. | |
| nonHeatingFraction | No | Share of that fuel used for something other than heating and hot water, such as a gas hob, as a decimal. A hob is usually 0.03 to 0.05. Defaults to 0. | |
| applianceEfficiency | No | Seasonal efficiency of the existing appliance, as a decimal. Defaults to the typical figure for the fuel. | |
| electricityPricePerKwh | Yes | Price of a unit of electricity, in pounds. Required. | |
| fuelStandingChargePerDay | No | Daily standing charge for that fuel in pounds, if it has one. A house that removes its gas boiler can usually stop paying this. | |
| electricityStandingChargePerDay | No | Daily electricity standing charge in pounds. It is paid either way, so it only changes the answer if the tariff changes with the heat pump. |
Output Schema
| Name | Required | Description | Default |
|---|---|---|---|
| fuel | Yes | ||
| scop | Yes | ||
| notes | Yes | ||
| method | Yes | ||
| verdict | Yes | ||
| references | Yes | ||
| breakEvenScop | Yes | The seasonal efficiency at which the heat pump costs exactly what the current system costs. Below this it costs more. | |
| annualDifference | Yes | Positive when the heat pump costs less. | |
| costPerKwhHeatNow | Yes | What a unit of delivered heat costs today, in pounds. | |
| currentAnnualCost | Yes | ||
| percentDifference | Yes | ||
| heatPumpAnnualCost | Yes | ||
| annualHeatDemandKwh | Yes | Useful heat the house actually needs in a year, after the existing appliance's losses are taken off its fuel input. | |
| applianceEfficiency | Yes | ||
| breakEvenPriceRatio | Yes | How many times dearer a unit of electricity is than a unit of the current fuel. Compare it with the SCOP: a heat pump saves money whenever the SCOP beats this ratio. | |
| costPerKwhHeatHeatPump | Yes | What a unit of delivered heat would cost from the heat pump. | |
| heatPumpElectricityKwh | Yes | Units of electricity the heat pump would use in a year. |