5 Factors That Affect Heat Pump Running Costs

Two identical heat pumps can cost very different amounts to run, and the reasons are all fixable.

1. Flow temperature (biggest impact)

Flow temperature is how hot the water leaving your heat pump is. Lower flow temperatures mean higher efficiency: a system running at 35°C flow can reach SCOP 4.0. The same pump recommissioned at 55°C flow drops to around SCOP 2.5, increasing running cost by roughly 60% for identical heat output. See our SCOP guide for the full curve.

To run low flow temperatures you need radiators sized for the lower output, or underfloor heating. Many UK homes have radiators sized for a gas boiler's 60-70°C flow. Upsizing radiators or adding extra panels allows 35-45°C flow, which is where most of the cost saving in this list comes from.

2. Insulation quality

Better insulation reduces total heat demand, so you use less electricity regardless of SCOP. Loft insulation at 270mm or more, cavity wall fill, and double glazing can roughly halve heat loss compared with an uninsulated home. Insulation also allows a lower flow temperature (factor 1) to still heat the home properly, so the two factors compound.

3. Thermostat settings and usage patterns

Heat pumps work best left on at a constant, moderate temperature (18-20°C) rather than switched off and blasted back up. Each 1°C rise in target temperature adds roughly 8% to running cost. On a time-of-use tariff, running the pump overnight on cheap-rate electricity and coasting through the peak window can save a further 20-30%; see our tariff guide.

4. Heat pump sizing

Correctly sized pumps run continuously at high efficiency. Oversized pumps cycle on and off, which reduces SCOP and wastes the higher capital cost of the larger unit. If your pump short-cycles (runs for 10 minutes, then stops), it is likely oversized for your actual heat loss, which is common when installers copy old boiler sizes. See our full sizing guide.

5. Electricity tariff

The standard variable rate is 26.11p/kWh under the current Ofgem price cap (Jul-Sep 2026)¹. Time-of-use tariffs such as Octopus Cosy offer around 14.5p/kWh off-peak but over 50p/kWh at peak. If you can shift 60% or more of heating to off-peak, you save money; if not, you can end up paying more than a flat tariff. Whether it works depends on insulation (can you store heat overnight?) and hot water tank size.

Other factors (smaller impact)

• Outdoor temperature: colder winters reduce SCOP slightly; Scotland averages 5-10% higher running costs than southern England for the same system.
• Hot water demand: heating water to 50-55°C is less efficient than space heating, so large families using more hot water see higher costs.
• Heat pump brand and model: top brands perform around 10% better than budget models in independent field trials.

Optimising your system

If your heat pump costs more than expected, check flow temperature first; ask your installer to measure and, if possible, lower it. Dropping from 50°C to 40°C can save upwards of £200 a year on a typical home. Next, check insulation if the home is pre-1990s with no cavity wall fill or loft insulation. Finally, consider a time-of-use tariff only if you have a large hot water tank and decent insulation to store heat overnight.

SCOP swing, 35C to 55C flow

4.0 -> 2.5

Cost swing from flow temp

~60%

Cost per 1C thermostat rise

~8%

Off-peak tariff saving potential

20-30%

Frequently asked questions

Related guides

Calculate your costs: Try the heat pump cost calculator to see how SCOP and tariff affect your bill.

Last reviewed: 3 July 2026.