Hi AmyFOD,

It can be difficult to convince people about the benefits of an ASHP from the efficiency point of view, when it is not easy to explain how you get more energy out than you put in.

First of all, just as with any form of heating system, ASHP's do not run constantly. They may be switched on so that they are available, but they only operate when there is a heat demand. Just like your refrigerator is switched on all the time, but you will hear the compressor start and stop periodically.

Direct electric heating is at best 100% efficient, so for each 1 kWh of electrical energy put in you will get 1 kWh of heat energy out. At it's worst an ASHP is at least 250% efficient, so for each 1 kWh of electrical energy put in you get at least 2.5 kWh of heat energy out. Direct electric heating would therefore be at least 2.5 times more expensive to run compared to an ASHP.

Using less energy is not only good for the planet but also for your bank balance.

Whatever your heating system it is important to have good insulation and controls that allow the operation of the system to be optimised.

I hope that the above helps you to convince your Mum.

Hi Derek, 

 Thank you for this, I will do my best to leverage what we can. I suppose my main concern is that there is a lot of information out there suggesting that they never really run as efficiently as they're supposed to and you need to get so much right to get it to work properly! I'm going to spend a bit more time looking through all the specifications and trying to work out if we've been offered the right sort of system. We're getting some more insulation put in and we've got old double glazing, although we're in a high radon area so have quite a lot of vents in the house, so that doesn't help. But then I suppose that doesn't help whatever kind of heating we have!

 Thanks for your help and advice.

Amy

Hi Amy,

During the warmer Spring and Autumn periods an ASHP should be 400% efficient or even greater, the efficiency starts to reduce as the ambient air temperature falls below +5C, but should still be of the order of 250% at -10C.

As you are in a Radon area, you may wish to consider Mechanical Ventilation Heat Recovery (MVHR), which uses the warm air being exhausted to heat the colder air being drawn in. There are now systems that incorporate an ASHP which makes the process even more efficient. The only drawback is that they don't qualify for any form of grant, since they are an Air to Air ASHP rather than the Air to Water type that most people have installed.

If your budget allows you may also wish to consider a solar PV system to help power the ASHP.

As an FYI we have a 12kw system. Today its been using around 2kw to heat our hot water, so somewhere in the region of 500%-600% efficient 2kw in 12kw out

@amyfod 

We too have recently moved to a high radon area.  Just got the test results back and investigating an exterior sump extractor type of venting.  Early days in our research yet.

It's also worth mentioning that heating in flats is a bit different from houses, because in flats you often have a lot of walls and floors that are heated by your neighbours.  So you have less heat demand, and so pure electric heat could make more sense.  Also you typically don't have a lot of space for a heating system, hence the popularity of storage heaters.  Whereas in a house you have more space and a lot more external walls that, even if well insulated, have cold exterior air on the outside.  So the balance may swing towards spending more outlay in installation versus less in running costs, versus a cheaper install but sky high running costs.