A heat pump for all

There are any number of myths doing the rounds on social media about why heat pumps “don’t work”.  One of the main ones is that heat pumps only really work in new, well insulated homes.

But that is simply not true.

We have installed heat pumps in solid brick houses, old stone farmhouses and even poorly insulated Listed Buildings and they work perfectly well, keeping our customers’ cosy and providing plenty of hot water.

The truth is that air source or ground source heat pumps can work in any building as long as they are designed, sized and installed correctly. As with any heating system, they just need to put as much heat into a building as it is losing to keep the house warm.

This is all down to some basic physics as our diagram shows.

A building loses heat through the walls, the floor, the windows and the roof when it is colder outside than inside, as shown by the stylised arrows in the diagram.

The upper panels show an outdoor temperature of 10C, and an indoor temperature of 20C.

Without insulation, shown in the left-hand panels, heat loss is higher – indicated by the larger arrows – and the heat input must similarly be increased to maintain a steady indoor temperature.

At lower outside temperatures – shown in the lower panels – more heat is being lost, for a given level of home insulation. Yet, as long as the heat input from a heating system is equal to the heat loss, the building will still retain its indoor temperature.

This means that for a poorly insulated home, a larger heat pump is needed, just as a larger gas boiler would be needed to reach the required heat input.

One of the longest running field studies of heat pumps in renovated properties, in Germany, shows that extensive renovations and insulation upgrades are not necessary to install a heat pump.

It’s true, good insulation will keep running costs down but that is also true for homes heated by gas and oil boilers.

Where heat pumps do differ is that they operate at lower flow temperatures to maximise efficiency, which means the water pumped to the radiators in a house will have a temperature closer to 50C or below, whereas fossil fuel boilers are typically set to provide water at 70C or more.

What this can mean is that with a heat pump, the radiators may need to be larger to achieve the same indoor temperature. At a 50C flow temp a radiator will need to be bigger to get the same heat into a room than if there was a 70C flow temp.

This may be where the myth comes from. Just putting a heat pump on to an existing rad circuit may mean the rads, at 50C flow temp, cannot get enough heat into the room when it’s below zero outside. And, therefore, the heat pump “doesn’t work”.

As mentioned, design is everything, which is why we at Biosun carry out a full room-by-room Heat Loss Survey on each property. This tells us how much heat the room is losing through the fabric of the building when it’s cold outside. From that we can ensure the rads are sized correctly to get that much heat into the room to keep the room at a cosy temperature.

The good news is that research shows that radiators are often oversized to begin with and that, as a result, not all radiators may need to be replaced.

That’s mainly because in the past plumbers have not carried out a Heat Loss Survey but have put in rads based on experience, knowing they will easily provide enough heat.

So next time you hear on social media, or from a friend down the pub, that heat pumps “don’t work” (and there are some genuine horror stories out there!) just point them to the physics. Or ask them to give us a call.

·       Sources for this post can be found in Carbon Brief Factcheck: 18 misleading myths about heat pumps