Heat Pump Sizing Calculator

Size a heat pump and compare running cost against a gas boiler.

About Heat Pump Sizing Calculator

A SCOP of 3.4 means each unit of electricity delivers 3.4 units of heat, which is what offsets the higher unit price of electricity. Whether running cost falls depends on the ratio between electricity and gas prices relative to the SCOP. Heat pumps must be sized to the actual heat loss rather than oversized, because oversizing forces cycling that reduces the achieved SCOP well below the rated figure.

Formula

Heat Pump Sizing

Electricity consumption = heat demand ÷ SCOP; capacity = design heat loss plus a small margin

SCOP: Seasonal coefficient of performance, heat delivered per unit of electricity
design heat loss: Heat required on the coldest expected day

Worked example

With the default values below, Heat Pump Sizing Calculator returns Heat Pump Capacity Required of 8.80. Change any input above and every figure here is recalculated in your browser.

Inputs used

Design heat lossminimum 0.1 kW: 8 kW
Seasonal coefficient of performanceminimum 1: 3.4
Annual heat demandminimum 0 kWh: 12,000 kWh
Electricity price per kWhminimum 0: 0.28
Gas price per kWhminimum 0: 0.07

Results

Heat Pump Capacity Required: 8.80 kW
Annual Electricity Consumption: 3,529 kWh
Annual Heat Pump Running Cost: $988.24
Annual Gas Boiler Running Cost: $933.33
Annual Running Cost Saving: -$54.90

Step by step

1Values used
2Heat Pump Sizing
3Heat Pump Capacity Required= 8.80 kW
4Annual Electricity Consumption= 3,529 kWh
5Annual Heat Pump Running Cost= 988.24
6Annual Gas Boiler Running Cost= 933.33
7Annual Running Cost Saving= -54.90

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or fees or charges into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Heat Pump Sizing calculated?

Electricity consumption = heat demand ÷ SCOP; capacity = design heat loss plus a small margin A SCOP of 3.4 means each unit of electricity delivers 3.4 units of heat, which is what offsets the higher unit price of electricity. Whether running cost falls depends on the ratio between electricity and gas prices relative to the SCOP.

Why does Heat Pump Sizing matter?

Heat pumps must be sized to the actual heat loss rather than oversized, because oversizing forces cycling that reduces the achieved SCOP well below the rated figure.

What values do I need to enter?

This calculator takes 5 inputs: Design heat loss, Seasonal coefficient of performance, Annual heat demand, Electricity price per kWh, Gas price per kWh. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.