ONE HEAT PUMP OR TWO?

Although one heat pump is considered the norm, here are the situations when it might make sense to double up

- DAVID HILTON

Legislation and the pursuit of energy efficiency in our homes is pushing homeowners to consider heat pumps as an alternative heating solution to fossil fuel boilers. But there are a few differences between the two technologies with the key one being that heat pumps do not deliver the same amount of heat that we get from a boiler.

We usually only need one boiler in a home, but in some cases we may require, or choose, two heat pumps to meet our energy needs. But is this necessary in every home? Are there key circumstances when it's more essential than others, what are the pros and cons and how do you make two heat pumps work efficiently together? Or is one sufficient?

HEAT REQUIREMENTS

Air source heat pumps do not always deliver the same amount of heat as gas or electric boilers. Most air source heat pumps are sized at an ambient air temperature of 7°C and a delivered water temperature of 35°C. If the air temperature drops or the required water temperature increases, the output decreases.

Heat pumps use electricity to run and if a home only has a single-phase electric supply then it is likely that the largest air source heat pump that could be connected to it will be around 16kW. However, a 16kW air source heat pump will often only deliver around 11kW of energy, at worst. This still equates to the amount of heat required by a 300m² home that is built to current Building Regulations standards, but anything above this - either in terms of the size of your home or factors influencing the amount of heat you need - could start to be problematic.

REASONS FOR TWO HEAT PUMPS

There are a number of different reasons why you may need more than one heat pump: