Air source heat pump questions and answers

by Mars

We have received hundreds of comments and questions regarding air source heat pumps from our YouTube channel and blog followers. We have answered most of the questions in writing, but we thought it was a good idea to collect the most common and relevant questions and answer them in this video.

The feedback we have received to our air source heat pump videos has been amazing, and we’d like to take this opportunity to thank everyone for their support and for watching. It’s greatly appreciated.

These are the full questions we’ve answered in the video.

Question 1

Which is best way forward: Green Home Grant (GRG) or Renewable Heat Incentive (RHI)? Nigel

Question 2

Look forward to finding out about the maintenance costs in your future videos as such info is more available for e.g. gas boilers, but wondering about the long term maintenance costs of ASHP. Flickafy

I assume these systems need a regular service check. Is it expensive? Endo

Question 3

Thanks for this set of videos. You touched upon your bills but you didn’t mention how much your electricity bill had raised post-installation of you ASHP (I understand all the provisos/solar panels, etc.) but would be interested to know. Thanks. Guy

Question 4

When you say that you keep your pump on all the time does that mean you keep it at 21C, 24 hours a day? I’ve been turning ours down to 19.5 when I go to bed. Can you just verify this? I’m thinking of the financial and efficiency side. We do not have underfloor heating just radiators. and we have solar panels too. Andrea

Question 5

In terms of water usage, can you run hot water continuously or will you run out of hot water quite fast? Sebastian

Question 6

How do you calculate the COP? I’m surprised that the house insulation is a factor in it. Wout

Question 7

When standing next to the heat pump outside how noisy is it? Rowan


anna mycoe 22 January 2021 - 09:02

Hi Mars
In relation to Q1. Something you mentioned didn’t ring true so I’ve had a read up and you do not need to inform the The dno approval is not needed in advance of installation. The dno is notified post installation with what is called “fit and inform” rules. It is noted on the mcs certificate.
The DNO respond, eventually, at their leisure. But just like with solar pv it can take them many week, if at all.
The dno notification is not needed for the RHI claim.
Hope this helps

Mars 22 January 2021 - 09:14

Thanks for the feedback Anne. Our process was definitely different as we received the DNO approval in advance of the installation and the heat pump manufacturer had to provide a detailed electricity consumption breakdown to the DNO.

Our approval, Form B, states: Use this form to apply to connect new or additional heat pump equipment rated up to 75A per phase that does not meet the requirements of standards BS EN 61000-3-2 and BS EN 61000-3-3 but meets the requirement of BS EN 61000-3-11 or BS EN 61000-3-121

This may have something to do with the sizing of the pump. We also needed DNO permission for our solar PV because we went with a large 6.16kW system that exceeded the maximum limit for not requiring permission.

I will look into the DNO and RHI, because from memory I recall we did have to submit this document for our system. I’ll look into this and update this comment when I have an answer.

Mark Crooks 22 January 2021 - 11:48

My experience was the same as Anna’s. All I needed for the RHI registration was the EPC and MCS certificates which contain info required for the registration forms.

Mars 22 January 2021 - 17:25

Thanks Mark. Interesting. Maybe I remembered that portion incorrectly, but I remember the DNO certificate was a requirement for something.

Mark+Crooks 24 January 2021 - 07:41

On the subject of electricity tariffs, do you have any data on when the ASHP uses power? i.e. time during the day. Particularly over winter.

I’ve just read up on Economy 7 and Economy 10 and wondered if those might be beneficial for ASHP systems.

Mars 24 January 2021 - 21:34

The ASHP consumes power when it’s on. So on cold days we idle at 3kWh throughout the day, 24/7. You can, of course, turn the ASHP off when you chose, during which time it doesn’t consume any electricity, but that will affect efficiency.

I have read a few articles where people with well insulated homes run their ASHPs over night, taking advantage of low tariffs using providers that require smart metres, and turn the ASHPs off during the day when consumption and tariffs are higher.

We looked into Economy 7, albeit briefly, because providers had no desire to install these metres.

The future will almost certainly be smart metres for everyone.

Name 26 January 2021 - 17:45

Well….you use yours during the day from the solar and during the night for economy whatever. Win-Win.

Andrew+Scott 1 February 2021 - 19:06

I have read a number of posts regarding a disappointing ASHP experience. This concerns me as it is likely that in the next few years, new oil and gas boilers may be phased out, certainly in new builds, so we will all be increasingly relying on electricity as our main source of heat for homes. Obviously the more electricity we can generate from solar and wind is key, but for central heating and DHW, heat pumps are the most economical technology for converting electrical energy into thermal energy whether ASHP or GSHP. A heat pump should have a COP of at least 3, in our climate, and should be nearer 4, so the technology is not a problem. This leads me to question what else can be at fault? If it is noise, then it may be that the heat pump in question has a manufacturing or design issue, or perhaps it is not installed in a suitable location. These things should not arise with a good heat pump and installation design. The main concern that I have is that if we are selecting heat pumps as a low energy heat source, then we need to ensure that the property is suitably insulated. With a new property built to current building regulations, it should be a given, but more of a challenge for older traditionally constructed properties. We built a new 160m2 house, of timber frame construction, suspended concrete beam and block ground floor, and with the floor, walls and roof insulated, our total energy averages £60 / month. Our solar PV obviously contributes a small amount, but more significantly the FIT payments are averaged at £50 / month, so our energy costs are just £120 / annum. If heated our house with direct electrical appliances, then I would not expect to pay more than about 3 times this, i.e. £360 / annum. To conclude I can only surmise that the poor performance is down to a badly designed system, or a poorly insulated building. In support of this, I also have a close friend who has a bungalow with an ASHP and UFH and also my nephew has a small bungalow with the same, and they are both warm, and pleased with their energy costs and systems, so I think the focus should be on the building and the heat pump contractor rather than the technology itself.

Mars 1 February 2021 - 21:57

I have to fully agree with everything you’ve said. I think there are a lot of ASHP models, from recognised manufacturers, that are inefficient and noisy, and it doesn’t help when they’re not commissioned properly. There have also been too many instances where incorrectly sized pumps have been fitted and don’t satisfy heating demands.

But it scares would-be first timers away, which is a shame.

Andrew+Scott 16 February 2021 - 22:47

Both examples of ASHPs I have experience of have the compressor mounted on heavy rubber blocks which in turn are mounted on an independent concrete plinth. If there are installers out there mounting them on a building wall using metal brackets, I am not surprised there are noise issues. In my examples, the only thing that you can hear indoors is the circulation pump, which is no different to any other traditional central heating system. The only other aspect would be ensuring no vibration is transmitted via the refrigerant pipes, which must have suitable insulation and flexibility in their connections. This is all about good installation practice. Noise should not be an issue or require additional accoustic enclosures to resolve in my opinion.


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