Energy efficient heat pumps are becoming popular as fuel prices soar

For the non-technical enthusiast, heat pumps seem almost too good to be true. You take the background temperature of the air or the ground and amplify it with your heat pump to warm your house. The best analogy for the layman is a fridge, which sucks the heat energy out of the food stored within and radiates it to the environment via that black metal grille at the back.

It’s hard to imagine that there’s any heat stored in a litre of milk, let alone the chilly air or soil outside your house. And it is true that the kind of heat pump used for heating buildings will not produce temperatures anywhere near those obtained from your oil- or gas-fired central heating boiler.

A domestic heat pump typically generates flow temperatures (the temperature of the water being circulated) of between 35 and 50°C. This is significantly lower than the flow temperature produced by a domestic gas or oil-fired boiler which is generally in the region of 60-70°C. But when combined with a wet (as opposed to electrical) underfloor heating (UFH) system, a heat pump will transfer more of this heat energy to the occupants of the building and do it more efficiently than a traditional heating system.

As a UFH system heats the entire floor, it does not need to reach the high temperatures of a wall-mounted radiator which has to concentrate the heat in a much smaller area. A further, practical advantage of UFH, is the fact that it occupies no wall space and is effectively invisible.

Ten years ago, most UFH systems were electrical. At the time, this was (and still is) one of the most efficient ways of using electricity for domestic heating. A well-insulated floor slab will act as a highly effective storage heater, requiring only a low-level of heat to maintain a comfortable temperature.

However, for the optimum low-carbon heating option, a wet UFH system, running off a heat pump wins hands down. A little electricity is required to operate the pump, but the inherent efficiency of the system means that for every 1kW of power consumed by the system, you extract 3-4kW of heat energy from the low-level background temperature.

The efficiency of a UFH/heat pump system can be further enhanced if electricity is generated locally – for example, from roof-mounted solar panels – to power the pump.

With the price of fossil fuels becoming ever more volatile and Building Regulations clamping down on carbon emissions, a low-energy heating system combining a heat pump and wet UFH is almost impossible to beat for efficiency, comfort and value.