The Seasonal Performance Factor (SPF) of Air Source Heat Pumps

Posted by Andi

Heat Pump efficacy…

Where the Coefficient of Performance (COP) effectively gives us a usable measurement of a Heat Pumps efficacy, the Seasonal Performance does the same but on an annual basis instead of at any given time. It is a much more useful measurement to use when calculating how efficient your Heat Pump will be overall seeing as it factors in all the seasonal changes we have in the UK.

Seasonal Performance Factor

As you may already know, Air Source Heat Pumps essentially use the ambient heat in the outside air to heat your home and although Air Source Heat Pumps can still function efficiently in temperatures as low as -20 degrees C it will require more electricity to heat your home than if the air was warmer. By using the Seasonal Performance Factor (SPF) we can factor in these changes in temperature and performance to give you an overall, accurate figure.

Seasonal Performance Factor…

For our more technical readers, the SPF of a Heat Pump is the ratio of annual heat generated to the annual electricity consumed for the operation of the heat pump. Meaning that we take the overall thermal energy output by the Air Source Heat Pump in a heating season, expressed in kilowatts (kW) and divide that by the total electricity, also expressed in kilowatts (kW) in the same heating season. By dividing these values, we will get the Seasonal Performance Factor of our Air Source Heat Pump. The formula can be seen bellow –


SPF = Total heat output per heating season / Total electricity consumed per heating season


By combining the Seasonal Performance Factor with the Coefficient of Performance you can build an accurate mathematical prediction of how efficiently an Air Source Heat Pump can heat your home and how much it will cost you, dispelling the idea that it will be “financially inviable” to heat your home in the winter months.  We also recommend that you read our article on the Coefficient of Performance (COP) so that your fully clued up on all of the Air Source Heat Pump related jargon and language that you may find useful.

The top photo is the Air Source Heat Pump we installed at Our Cow Molly.

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