One thing that you cannot do is build a box around your ASHP, since it would prevent it from working efficiently, make it work harder which would make it much noisier. 🙄 If space allows you may be able to put a fence or some bushes at your neighbor's side to help absorb the sound waves.

Please provide more details, with photo's, and we will try to provide helpful advice.

I have some experience in noise assessment using BS4142 and BS8233 and also noise mitigation, but this is mainly for electrical substations and similar electrical infrastructure developments.

Some photos of the ASHP would be useful and maybe some drawings (with distances) of where the ASHP is in relation to your neighbour's property and their general amenity area.

A few questions/comments from my side:

• Has the ASHP noise output been shown to be compliant with the manufacturer specification?
  • I.e. is it in line with expectations from a sound power level perspective?
• Related to the above, is the planning permission dependent on the emitted noise from the ASHP or the noise at your neighbour's property?
  • What dB limits are you having to adhere to? Is it a set LA90 or LAeq limit? Is it 1/1 or 1/3 octave band dependent? I assume it is based on external noise and not internal (like an NR curve or similar)?
  • How much are you exceeding the limits by (assuming you are)? Is the exceedance general broadband noise or is it tonal? 
  • Is the noise nuisance present all the time or during the night or other times of year for example?
• Was any sort of noise impact assessment done ahead of time by the installer to at least model compliance with the noise limits?
  • This is to see how far you are in reality from what was assumed.
• Is the ASHP near a reflective/hard surface enclosed area?
  • Could be exacerbating the issue with reflected noise from the device.
• A bush/vegetation won't really do anything to mitigate the noise but it would enhance the natural broadband noise when the wind blows slightly, meaning the ASHP noise would be masked slightly when the wind speed is higher.
  • However BS4142 usually considers noise during quiet periods and low wind (having done many fairly drab noise surveys on quiet nights I know this to be the case).

Hi @ericdo. Noise is a difficult subject. MCS 020 noise assessment guide is a rough estimate tool for installations to check, on paper, dB(A) theoretical sound pressure level [SPL] at nearby proximities.

MCSCERTIFIED.COM "https://mcscertified.com/wp-content/uploads/2021/10/MCS-020.pdf"

A general acceptance criteria of 42dB(A) at the nearest occupied dwelling from the ASHP is required for permitted development noise level compliance. That's quite high, as night time background noise is assumed in MCS 020 as 40dB(A), whereas it can be nearer 30 dB(A) in reality.

Manufacturer's dB(A) data is quoted 'free field' with no reflective surfaces, usually at 1m from source. Sitting an ASHP on a patio adds 1 reflective plane +3dB(A). Sitting on a patio and against a wall adds 2 reflective planes +6dB(A), sitting in a corner on a patio with two reflective walls at 90deg adds 3 reflective planes +9dB(A). This is the 'directivity' of the noise, and whether the ASHP location is reflecting [amplifying the free field] noise in direction. This can result in a measured dB(A) SPL value much higher than the manufacturer's free field data.

That's often where issues start, the ASHP location, with sound energy reflected in one particular direction. You cannot completely enclose the ASHP with an acoustically absorptive structure without seriously impeding airflow and efficiency. It may be practical to install acoustic screening however, if the noise is generally emitted and reflected in one direction.

1. Photos of the installation, location of ASHP, distance to complainant's property.

2. As measured noise levels, presumably from your acoustic survey. How far wide of the 42dB(A) permitted development criterion are they?

3. What's the dominant noise? It is the fan, it is the compressor? Most ASHPs have acoustically cased compressors, usually the dominant noise is the axial fan. Fan noise is broad spectrum 'white noise' and relatively easy to attenuate. Compressor noise can be tonal and lower in frequency, more of a hum, which travels further and is harder to absorb.

Bushes and plants are almost acoustically transparent, they will not really help. Ugly though they are, acoustic screens and acoustic absorption added to reflective surfaces adjacent to the ASHP are the only effective solution to attenuate noise. If there's no space to install that, relocation of the ASHP may be the only option. Pipe runs can be well insulated in conduit and underground, and can increase in diameter to compensate for increased pipe run length. Unfortunately either solution is going to involve some expense.

It really is absurd. Some fired boiler flues are much noisier than ASHPs, one of my neighbouring properties has a particularly noisy oil fired room sealed flue outlet.

• At time of sale, the MCS assessment was done with a recommended install location. (In retrospect,  I am 100% convinced that it was wrong.) There was no detailed noise assessment
• I asked them to move it approx. 1.5m away from their recommended spot to the boundary of the house. My bad. Naively I thought 1.5 m would make no difference, as it was behind a fence and the neighbour could not see it. I did not take into account noise.
• Neighbour lodged planning complaint.
• Council said I was in breach of planning, and told me to apply for planning. Told during planning to meet BS8233. 
• During the planning process, neighbour also launched a noise compliant. 
• Council told me it was likely that there was a "statutory noise issue". No noise abatement notice has been issued to me.
• As part of planning, the  (~£1k) noise assessment report (attached) showed that I was inside BS8233.
• Planning approved with a condition that I mitigate noise to the level of BS4142. Made no reference to the £1k report they had told me to get. The condition says Design to be submitted for approval within 3 months. Once approved, Design to be implemented within another 3 months.
• I ignored them 🙁
• Planning enforcement officer came round and told me to get on with it
• I launched a complaint with council about them changing their minds between BS8233 and BS4142 halfway through the plannign process.
• As you can image the complaint process came back and told me tough -  I had to suck it up. 
• Having spoken to the guys who did my BS8233 assessment, it looks like to meet BS4142 I need to reduce noise by 23dB in order to meet background noise of 33db overnight

1. Spend ~7k on an enclosure to reduce noise by 23dB (specs attached). I'm still finalising designs and getting the council to confirm that I have understood planning conditions correctly
2. Move the ASHP approx. 25-30m away from where it is now (diagram attached) I would need to get a mini digger in to remove concrete under driveways etc and pay someone to lay out new pipework. Includes 3x 90 degree bends and some elevation issues
3. Go back to a Gas boiler 🙁 estimated costs £3k plus the loss of £8k~RHI payments over the next 5 years

• Are there any metrics that I can use to assess the efficiency degradation if I put the enclosure around it. I appreciate everyone saying don't build a box around it, but clearly there are products designed just for such things
• Are there any metrics that I can use to assess the efficiency degradation if I move it (and add ~25m of underground piping)
  • Any special piping/insultion requirements
  • How do I make it cheap?
• Anyone got any experience on building a DIY enclosure - i.e. build small timber shed around it with the same s-bend airflow principles as the £7k enclosure, just line it really well with sound dampening material

Hi @ericdo, thanks for update. You’re sadly in a difficult situation. The LA moving the goal posts part way through is par for course.

An acoustic enclosure of the type shown would be detrimental to your ASHP performance. (I can bring a career in HVAC & refrigeration design to bear). It has been designed solely to passively attenuate the ASHP noise level with little regard for the impact on ASHP performance. The ASHP internal fans are not designed to accommodate any additional restriction. An enclosure would inevitably add restriction to the evaporator airflow. It could also cause short circuiting of air within the enclosure. I doubt very much it would be a wise option, technically is not a proven solution, and at £7K is cost prohibitive. I fear relocation of the ASHP may your only option if you wish to keep your ASHP.

The irony is that you could have a room sealed combustion boiler flue on the wall of your property facing your neighbour, which might well generate a higher noise than your ASHP….

Posted by: @ericdo

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Move the ASHP approx. 25-30m away from where it is now (diagram attached)

Are you sure this proposed location has sufficient air-flow? Will it fall within 1m of the boundary (thus ruling itself out of permitted development)? And will the council accept this retroactive permitted development?

By the way, what size is the currently installed pipework under the concrete? I just wonder whether moving the outdoor unit further down that fence is possible; far enough away that MCS-020 applies (the wooden fence probably does not count as substantial from a noise perspective). One could bodge together an overground pipe run, provided UV resistant pipe insulation is used. Your heat pump requires 34.5 litres/min of flow, suggesting an internal diameter of about 28mm for a 1m/s flow.

Other members of the forum might be able to provide pressure drop calculations to see whether your existing pipe plus some cheap 32mm MLCP might do the job! Assuming the use of 19mm Armaflex HT (0.042 W/mK) with a temperature difference of 55 degrees (very much worst-case as plastic pipe insulates better than copper) I guesstimate heat loss at 3.14 * 0.032 * 0.042/0.019 * 55 = 12W/meter of pipe run. So to put the outdoor unit 15m down the garden you'd be looking at 360W of losses on the coldest day.

@ericdo

I am not an acoustics expert, but I do try to apply the laws of physics and common sense to try to resolve problems.

What we as humans understand as noise is the variations of air pressure at our eardrums. I think that I am correct in saying, the greater the pressure change, the louder the noise. Another determining factor is the distance from the sound source, which I believe reduces as a square law, as one moves further from the source.

So, how to reduce the sound level at your neighbour's side of the fence?

As you have noted, one way is to move the heat pump further away from your neighbour. As you have also suggested, an alternative is to try to reduce the sound level.

I was surprised to see that your installer sited your heat pump closer than 1 metre from the boundary fence, which is not allowed under permitted development criteria. Rather than move the heat pump to the other side of your property, can you site it further from the fence at the present side?

Heat pumps are much louder when they are working harder, so you should try to ensure that your heat pump is operating as efficiently as possible. Are there any particular times of the day when your neighbour would prefer lower noise levels? You may be able to agree with your neighbour to reduce heat pump use during those periods.

Lowering noise levels in areas around your heat pump can also involve assessing the surfaces in the vicinity. Sound will be reflected from a hard surface and could create amplification in certain areas. If a rubber ball is thrown at a brick wall it will bounce off, if something like a blanket is hung in front of the wall, the ball will be stopped and drop to the floor.

For efficient operation a heat pump requires an adequate flow of air through the unit. Warmer air needs to be drawn in at the rear and cooler air flows out at the front. An acoustic hood completely covering the heat pump may interfere with the airflow and not only make it less efficient, but could also cause an increase in noise levels produced since it may be working harder.

I would therefore suggest that you try hanging some blankets or similar material on the fence at the rear of your heat pump, at either side at a distance of 2 metres, and possibly above your heat pump. Also try a similar technique in front of any hard surfaces in the vicinity of your heat pump. Install each one in turn and try to assess if any cause the desired reduction in noise levels. Once you have an assessment of the noise direction and reflections, it may be possible to design a suitable acoustic hood that reduces noise levels without unduly affecting your heat pump operation.

If you are on reasonable terms with your neighbour, perhaps it may be diplomatic to involve them in the testing process, to prove that you take their concerns seriously and that you are working to achieve an acceptable solution. Your neighbour may then withdraw their complaint, which could in turn reduce the requirements being specified by the council.

I am having similar arguments with my local authority, albeit pre-implementation, and a number of things have become clear which might help you think through this: In no particular order:

1. You need to keep a clear head about this, as they haven't issued an enforcement notice, you haven't lost yet

2. Planning law and environmental health law are completely separate.  So you can be compliant with one and not compliant with the other. (either way round!).  They are enforced by the same local authority, but that doesn't mean that there is any coherence between the two as they have origins in different and unconnected legislation. 

3. The planning requirements under express consent (ie when you submit a planning application) and the planning requirements under PD are completely separate. The former is determined by statute, the latter by the Local Plan, and they are unlikely to be coherent.

4. The planning department will likely ask environmental health for advice when considering a planning application, but the advice given will be against the standards set out in the local plan, NOT the standards under environmental health law.

5. It is very likely indeed that the requirements imposed by planning (express consent) will be much more severe than the requirements that environmental health can actually enforce:

• To sustain and enforcement under EH the LA would need to demonstrate that the noise ‘unreasonably and substantially interferes with the use or enjoyment of a home or other premises or injures health or be likely to injure health’. I'm not a lawyer but I cant imagine that this could be substantiated if you meet WHO guidelines.

• However to sustain and enforcement under planning law the LA would only need to demonstrate that you do not have planning consent (express or under permitted development). If their local plan requires, for example, that noise form an ASHP must ‘cause no detriment to neighbours amenity’ (as mine does) then that's a much more stringent (and frankly unachievable) noise standard than under EH law.

• there are effectively three levels in play namely: (a) the noise requirement under PD, (b) the noise requirement under EH law and (c) the noise requirement under express consent. Very likely (b) is much less stringent than (c), and possibly less stringent than (a)

6. Permitted development is permitted development, the LA cant ‘choose’ whether to accept it or not, either it meets the requirements of PD or it doesn’t. If it does the LA cannot enforce under planning law

7. If you are going for express consent the LA cannot refuse solely on the basis that it is retrospective. They have to judge it in exactly the same way as a new application.

8. Despite the fact that the bodies of law are separate, they local authority will conflate EH Law and Planning Law when it suits them, but short of actually issuing an enforcement notice when they would have to be strict about the matter. The underlying motivation is to mitigate complaints, but without having to come down on one side or the other or fight a court case.

9. If you can satisfy your neighbour so they withdraw the complaint, then, as @derek-m  says, try to do so, but be aware that it may not solve the problem. Equally your neighbour may be determined to kick up a fuss in which case there may be little you can do to satisfy them, in which case concentrate on the law.

11.  Similarly the suggestions for noise mitigation above might help you not to breech EH or planning law, however if the Local Plan is anything like mine, the latter may be nigh on impossible unless you conform to PD rules so that the local plan becomes irrelevant.

12. Whilst the LA would definitely struggle to sustain an enforcement under EH law if the complaint is withdrawn, they may have the bit between their teeth as regards planning law, so you should try to find a way to comply with this also (probably by bringing the installation within the rules of permitted development).

13. You could try asking questions which force them to advise you separately the requirements under the local plan (planning law) and under EH law. They will likely try to avoid doing this because it restricts their ability to conflate the two, but you are entitled to know so you should push the point.

14.  Whilst BS8233 is a noise standard, BS 4142 is, ASFAIK, a standard for assessing noise, not an actual standard as regards the level of noise.  Most likely the LAs requirement is that you meet BS8233 as a means to demonstrate that you are not causing a statutory nuisance (which gets Environmental health off your back) but that you meet some much more stringent standard (as defined in your local plan) to be assessed using the methods in BS 4142, if you want express planning consent (note again how there is no correlation).

In summary my advice is to think carefully and separately about three things

1. How to comply with planning law (under PD or, much less easily, under express consent)

2. How to avoid causing a statutory nuisance (my reading is that you almost certainly have already demonstrated that this is the case – albeit that the LA havent told you that yet because it doesn’t suit their cause – so ask them!)

3. If and how you can get to the point where the neighbours withdraw their complaint

If you achieve (3) then (2) will almost certainly fall away but (1) may well not particularly now that the LA has been alerted to the issue.  When assessing planning applications the reference document is the local plan, not what the neighbours think!

If you cant achieve (3) then you probably need to achieve both (1) and (2)

I hope that helps you think about the matter. You haven't lost yet, they haven’t issued an enforcement notice (which may well because they dont think that it would be sustainable)!

@ericdo

Further to my comments above can you seem to imply that you have received express planning consent (because you refer to what I interpret as a condition), but I couldn't find it on the planning portal.  To be honest there were lots of applications for your address - which I presume to be the one on the noise report - but I couldn't find one which had ASHP in the description and I wasn't going to look through them all! 

So if you would care to answer the following I might be able to make some more specific comments supplemental to the general guidance above - which I still recommend you read carefully!):

• Have you received (or been denied) planning consent, if so what it the application reference (I will look it up on the portal)?
• If you have not received (or been denied) planning consent, in what context did this occur: "Planning approved with a condition that I mitigate noise to the level of BS4142. Made no reference to the £1k report they had told me to get. The condition says Design to be submitted for approval within 3 months. Once approved, Design to be implemented within another 3 months."

A skim read of your local plan suggests that it is much better in relation to this issue than the one in my District, so you have a reasonable chance with planning if you can tick the boxes, and the noise assessment seems to show that you meet reasonable EH requirements.