Heat pump sizing principles

Principles of heat pump sizing based on property energy requirements.

Heat pump sizing considerations

A heat pump is usually sized to provide 85% of the peak heating power of the house on the coldest day.

Since the number of days that this requirement occurs is relatively low, taken as a proportion of the total year, the heat pump is typically sized to provide 95% of the total energy required for heating the property over the year.

The remaining energy is provided by the built-in electrical heater.

The benefit of sizing the heat pump below the peak load requirement is that the pump, for the majority of the year, is able to remain on and deliver a ‘trickle charge’ of heat to the property, rather than being oversized and constantly cycling in and out of operation. This helps the heat pump to offer better efficiency.

The graph below is intended to show the principle behind the sizing of heat pumps to take into account the small number of hours where the peak heating load of the house is required. The dotted vertical line and red area show that there have only been 100 hours of outdoor temperature below 0ºC in the given 8,760 hours (number of hours in a year).

There are significant climatic differences across the UK and the example above is not intended to provide information on any particular installation.

Heat pump sizing services

We offer sizing services for ground source heat pumps and air to water heat pumps.

Read more about heat pump sizing services
Please note that this link will take you to the specifier area of this website.