Seasonal Performance Factor (SPF)

The Seasonal Performance Factor (SPF) is a measure of how efficiently your heat pump is operating. Put simply, the higher your SPF value the more energy efficient your system is.

Your heat pump needs electricity to run (it powers the compressors). To keep your heat pump running as efficiently as possible (and electricity bills as low as possible) your property should be well insulated and have a low temperature heating system, such as underfloor heating or low temperature radiators. The lower the temperatures and the bigger the area of your radiators, the less electricity your heat pump will use and the higher its SPF will be.

Why is the SPF important?

The SPF is used to calculate the renewable portion of your heat pump’s heat output. The regulations require us to deduct the electricity used to run the heat pump from the heat it delivers. Only the renewable portion of the heat generated by your heat pump can be used when calculating payments.

To be eligible, all heat pumps must have a minimum SPF value of 2.5.

The SPF is a factor in payments calculations using the following formula:

Estimated annual renewable heat load (total heat demand x (1– 1/SPF)) x tariff rate
Worked example
Total heat demand 15,000kWh
SPF 2.7
ASHP tariff rate at start of scheme 7.3p/kWh
SPF calculation (1-1/SPF), (1-1/2.7) = 0.63

Estimated annual renewable heat load (total demand x (1 - 1/SPF)

15,000kWh x 0.63 = 9,444kWh
Total annual Domestic RHI payment (tariff x estimated annual heat load) £689
Quarterly Domestic RHI payment (total annual Domestic RHI payment / 4) £172.25

If you have a heat pump, until 25 March 2016, your installer will either calculate the SPF using the Heat Emitter Guide, or take the SCOP value from the MCS website. From 26 March, they will only use the SCOP. This number will be entered directly into the MCS database when the renewable technology is registered and will be the number used when calculating RHI payments. For more information on this, please see our helpsheet ErP and the Domestic RHI.

What if I’m metered for payment?

If you are metered for payment, your quarterly payments are based on actual meter readings where the electricity used is deducted from the heat output, so calculating the renewable heat generated. 

Your SPF is still important. Your quarterly payments are based on your metered output BUT you will not be paid more than a set payment amount. There is a payment cap set so that you will not be paid more than you would have received if you were deemed. The payment cap takes into account your SPF and is based on your property’s estimated annual renewable heat load.

The SPF will be used to calculate the maximum amount you can be paid per year using the calculation in the following worked example:

Using the worked example above:

Annual Payment CAP = tariff x estimated annual renewable heat load:
7.3p x 9,444kWh = £689