Common heat pump myths.

Having replaced my gas boiler with an air source heat pump in a 250 year old semi-detached cottage that drastically reduced my carbon footprint, energy consumption and energy bills, I would like to address many myths that I was faced with along this journey.

1. Heat pumps won't work in older buildings without extensive, expensive insulation.

Insulation is certainly very important but in my 250 year old cottage I did basic draught proofing, the windows were already double glazed, and I topped up the loft insulation. This was very cheap. I was not confident about the expensive insulation for the outer walls by either exterior or interior methods.

2. Heat pumps won't work in the cold weather.

Heat pumps are used extensively in Norway, Sweden and now I have the experience of having a heat pump in Scotland with having no problem over the last three winters. 

3. Heat pumps are noisy.

I have to stand within about 3 metres of my heat pump to hear it. Since it is outside I never hear it when I am in the house. I often heard my gas boiler coming on in the morning before I got up 

 4. Heat pumps are expensive to run.

With a coefficient of 350% (or a COP of 3.5) bills are 3.5 times cheaper than direct electric heating or a bit cheaper than gas. (In a more modern well insulated house you  can achieve efficiencies of around 500%). Also with using off peak electricity the price can be further reduced considerably. During peak tariff times when the grid is more carbon intensive it is easier to use stored electrical energy. I estimate that my heating bills will be at least half that if I was using gas.

5. You need to have an efficiency or COP of 3 or above to reduce your carbon footprint.

This assumes the electricity to run your heat pump comes from burning gas in a power station instead of burning gas in your gas boiler which is a little bit more than twice as efficient. However it also assumes that ALL your energy comes from burning gas. Clearly this is not the case and every year the electricity is becoming greener and will continue into the future getting more so. Furthermore you can choose times of the day when the grid is greener and avoid the less green times by thoughtful yet easy management.

6. You need to run your heat pump 24/7 at a constant room temperature demand on purely weather compensation.

The confusion here is that running efficiency is the same as low consumption.

You do greatly benefit by running your heat pump “low and slow” on weather compensation but a compromise is needed between just at the moment you need heat and running it all the time.

This article here might explain how to get the best out of your heat pump in different situations.

As an aside I have seen the same mistake being made several years ago with comparing filament light bulbs with an at the time modern decor lighting with mini halogen light bulbs.

Two houses were given an energy performance certificate or EPC. The house with a kitchen and living room with two 40W filament light bulbs had a negative comment regarding the lighting. The house with three arrays of twenty 20W mini G4 halogen bulbs were given a tick for energy efficiency. The company doing the certificates told me that is the way the algorithms work. So 1.2 kW was preferred to 80 W because the efficiency of each bulb was better!

It can get sillier than that. I have heard people talking about how much energy they are saving if all their halogen bulbs had been filament!

 OK. We have LED bulbs now with higher efficiencies but the same principles can exist 

So what about heat pumps today?

It seems that many with heat pumps consider that the COP is a measure of how efficient the system is. However that is running efficiency and not necessarily overall efficiency. A modern well insulated house will need little heat and will retain it's heat well. This means that it will run at lower flow temperatures and have a better COP than a less well insulated house. Running 24/7 will mean it will not need much extra energy to keep the house warm all the time and the difference in consumption will be small. However in a less well insulated house, heating your house too far in advance or at times when the passive gain is enough to heat your home can mean quite a significant unnecessary increase in consumption.

Getting silly:- You can get a really high COP if you run your heat pump when the temperature outside is high enough for you not to need it running. Clarly it is lower consumption at times when the energy supply is greener without stressing your system that is the goal and not running merely running efficiency.