2x air source heat pumps - Scotland

[BintyAndTheBeast]

Hi all,

 

We are looking to get 2 air source heat pumps installed to our home but council are asking for Noise Impact Assessment to be carried out as part of planning as unlike in England this doesn't fall under permitted development rules. I'm trying to find a way around this to get the project moving again.

 

House:

5 bed detached home in Perth & Kinross Council area. Currently heated by an oil boiler, unvented 300l cylinder, underfloor heating downstairs, radiators upstairs, towel rails in bathrooms.

 

Planned system:

Vaillant aerotherm plus 10kw air to water to run downstairs underfloor heating and towel rails, plus new 400l unvented cylinder

Daikin 5MXM-A8 air to air ducted unit to provide heating (& cooling) to all bedrooms and the 3x upstairs bathrooms. 8 ports in total. This will also heat (and cool) an outdoor building that I use as an office. Radiators to be removed from bedrooms.

 

Installation:

We are installing the 2x outdoor units approx 11m from our gable wall where our oil tanks are currently sited. This will be approx 8+m from utility door and 9+m from bedroom window of our neighbour.

 

Issue:

Planning officer has stated environmental health have requested a Noise Impact Assessment to confirm no impact on neighbour. I've only found 1 consultant who can do this and they want £3k+vat. There's no alternative other than to go via Permitted Development Rules of a single heat only heat pump. 

I'd argued that I can install a single ASHP under PDR and then 6 months later install the second unit as an extension to the existing PDR as no change to fabric and will be using same material. He went away and came back to say that's not acceptable and would be challenged.

 

Question:

How do I get round this to get the 2 units installed.

I am aware that Scotland has consulted and recommendation is to bring in MCS 020 into PDR north of the border in "early 2026". Does anyone have an inside scoop on this to confirm it will definitely happen?

If that's the case I will withdraw the planning application, install the whole lot, except the Daikin outdoor unit, now and have our contractor return to for the unit only when allowable under PDR. This will save having to get the 11m of external pipework and electrics laid twice, which will be installed in a hand dug trench 750mm deep. 

Does this sound reasonable to allow the work to go ahead and start as planned now, or would the local authority say this isn't acceptable as we have already started the development of the air to air unit?

 

We have a £2k grant available from our mortgage provider which is claimed by submitting a paid invoice by 1/2/26, hence my desire to get moving sooner rather than later.

 

Any help appreciated!

[JohnMo]

I would temp back and really ask yourself why you need 2x heat pumps. Blown air in bathrooms will not be the most comfortable way to heat, especially if you are wet.

 

Have you done a full heat loss survey?

[ProDave]

Obvious question WHY 11M from your ow house?  Difficult without seeing a site layout but logic would say if closer to your house they would be further from neighbours so less likely to be a problem.

[BintyAndTheBeast]

22 minutes ago, JohnMo said:

I would temp back and really ask yourself why you need 2x heat pumps. Blown air in bathrooms will not be the most comfortable way to heat, especially if you are wet.

 

Have you done a full heat loss survey?

We are looking to remove fossil fuels and make the house as comfortable as possible. Towel rails are only just passing the output requirements and we dont really want to change them, so bathroom ducts will be used to top up heating only when needed. 

 

Heat loss at 7.94kW

[JohnMo]

Just now, BintyAndTheBeast said:

Heat loss at 7.94kW

Is that whole house?

[BintyAndTheBeast]

18 minutes ago, ProDave said:

Obvious question WHY 11M from your ow house?  Difficult without seeing a site layout but logic would say if closer to your house they would be further from neighbours so less likely to be a problem.

Back to back against the gable wall would, of course, be preferable, but we have 2 very large sheds only 2m away from the wall. Installing a heat pump / 2x heat pumps would make this a difficult space to get through with dogs, wheel barrows, etc. Placing the external units where the oil tanks are currently means they are out of sight of everyone.

[BintyAndTheBeast]

4 minutes ago, JohnMo said:

Is that whole house?

Yes, whole house heat loss carried out by Heat Geek of 7.94kW. 

House but in 2012, is around 320m2 and has great insulation. Rear of house has a lot of windows for solar gain. 

Edited December 29, 2025 by BintyAndTheBeast

[JohnMo]

Well you don't need two heat pumps, anyone that says you do, well!!!

 

I have house heating connected to a summer house, it has a very different heating characteristics to house. So I would just install a through wall Aircon unit in the out building - these are not subject to planning or permitted development as there is nothing visible (no box outside).

4 minutes ago, BintyAndTheBeast said:

house heat loss carried out by Heat Geek of 7.94kW

Then do one ASHP, to drive UFH, via an electronic mixer (driven by ASHP controller) and a second zone running fan coils. Get a heat pump that does cooling out the box (Vaillant don't), then have UFH - in cooling mode for summer and fan cols in upstairs.  All done under permitted development and all allowed under the grant scheme.

[BintyAndTheBeast]

9 hours ago, JohnMo said:

Is that whole house?

Yes, while house heat loss carried out by Heat Geek of 7.94kW. 

House but in 2012, is around 320m2 and has great insulation. Rear of house has a lot of windows for solar gain. 

[BintyAndTheBeast]

Thanks for the reply JohnMo.

 

Our installer touched on a single system but said we wouldn't get the same individual room control this way and Daikin was the leader for the ductless option we are looking for upstairs. 

If we can get the same overall comfort levels and individual room controls for bedrooms then your suggestion is definitely something I would want to consider. 

 

What would the differences be between the option we are currently looking at and the option you have suggested please? 

 

We are keen to remove radiators from bedrooms and not have wall / ceiling units, so the Daikin option was what was sold to me as a perfect system with only an 8" vent in bedroom ceilings.

 

We have only underfloor heating downstairs so guess we could cool floors on the warmer days too if needed. Our dogs would certainly appreciate that option!

[SBMS]

1 minute ago, BintyAndTheBeast said:

Thanks for the reply JohnMo.

 

Our installer touched on a single system but said we wouldn't get the same individual room control this way and Daikin was the leader for the ductless option we are looking for upstairs. 

If we can get the same overall comfort levels and individual room controls for bedrooms then your suggestion is definitely something I would want to consider. 

 

What would the differences be between the option we are currently looking at and the option you have suggested please? 

 

We are keen to remove radiators from bedrooms and not have wall / ceiling units, so the Daikin option was what was sold to me as a perfect system with only an 8" vent in bedroom ceilings.

 

We have only underfloor heating downstairs so guess we could cool floors on the warmer days too if needed. Our dogs would certainly appreciate that option!

Your installer is incorrect and @JohnMo advice is best. We are installing a Panasonic aquarea (t cap) system That is pretty much exactly what John described. One heat pump outside (probably a 9kW would

work for you). Inside then we have UFH on ground floor and 7x wall mounted fan coils (one for each bedroom plus landings). The fan coils are pretty much exactly what you would see internally with air conditioning. The fan coils provide heat from heat pump in winter. In summer the unit reverses and provides chilled water. This goes to the UFH slab to cool and to each individual fan coil. Each one is individually controllable. We have lagged our pipes feeding the fancoils so we can run this water very cold to produce very cold air (if needed). Others have said unnecessary and you can run above dew point but we are new build so easy to do now. Sounds like you’re doing a lot of work (ducting etc) so I would advise the same. Aquarea supports two zones and mixes to two temps so slab can be run above dew point. 
 

Aquarea also supports a ducted option with a large FCU and manifold exactly like air conditioning setup You want so You could

do That instead of wall units. The aquarea ones are quite stylish though. 

I found a lot of installers only recommend what ‘they know’.

 

I’ll be honest I’ve had to have Panasonic come out and walk my installer through it all because it’s not hugely common setup but is a lot easier, cheaper and does away with your planning issue. 

[BintyAndTheBeast]

Thanks SBMS, that’s a helpful reply.

 

I spoke to my installer and as a Panasonic preferred partner he would be able to get us a 7 year warranty. Unfortunately he doesn’t recommend we install due to a number of issues. The ones I can remember include slow access to parts, poor condensate draining, very loud operation (confirmed from spec sheets against the Vaillant and Daikin units we are planning), poor web/app interface, poor build quality (he spoke about plastic trims going brittle and breaking; fan bearings failing early), and a couple more issues. He was installing roughly similar numbers of Panasonic and Vaillant but failure rates & call backs were multiple times higher on Panasonic so he will now only install if directly requested by the customer.

 

Other points he’d mentioned was that we asked for 6+ ducted zones and Panasonic will only have capacity for 5 unless we went for wall units, which we are keen to avoid. He’s also suggested that as we are going for low and slow heating/cooling the vents rather than forced air from all unit/cassette would be preferable. Apparently the Daikin ducts are significantly quieter too.

 

Im not sure whether he’s a good salesman or if I am gullible but I think the existing plan would be a better option, and also have a nicer finish for my home office. Shame, as this had great potential for a compromise for our wants (I understand they’re not needs).

 

My current thoughts are to do the planned install and come back to install the second external unit when Scotland catches up with the rest of the country to allow 2 units without planning permission.

[SBMS]

10 minutes ago, BintyAndTheBeast said:

Thanks SBMS, that’s a helpful reply.

 

I spoke to my installer and as a Panasonic preferred partner he would be able to get us a 7 year warranty. Unfortunately he doesn’t recommend we install due to a number of issues. The ones I can remember include slow access to parts, poor condensate draining, very loud operation (confirmed from spec sheets against the Vaillant and Daikin units we are planning), poor web/app interface, poor build quality (he spoke about plastic trims going brittle and breaking; fan bearings failing early), and a couple more issues. He was installing roughly similar numbers of Panasonic and Vaillant but failure rates & call backs were multiple times higher on Panasonic so he will now only install if directly requested by the customer.

 

Other points he’d mentioned was that we asked for 6+ ducted zones and Panasonic will only have capacity for 5 unless we went for wall units, which we are keen to avoid. He’s also suggested that as we are going for low and slow heating/cooling the vents rather than forced air from all unit/cassette would be preferable. Apparently the Daikin ducts are significantly quieter too.

 

Im not sure whether he’s a good salesman or if I am gullible but I think the existing plan would be a better option, and also have a nicer finish for my home office. Shame, as this had great potential for a compromise for our wants (I understand they’re not needs).

 

My current thoughts are to do the planned install and come back to install the second external unit when Scotland catches up with the rest of the country to allow 2 units without planning permission.

Fair enough but check if your installer is talking about the newer generation. The newer model is 33dBA at 3m for example vs vaillant’s 54dBA so not sure which spec sheets you were looking at with regards noise?

[BintyAndTheBeast]

Thanks again for this. 

 

For the noise it was the internal unit he mentioned specifically. I don't remember exactly but we would need the bigger ducting option of 2 available and it was considerably louser in operation than the Daikin option. 

[JohnMo]

You seem dead set on two units, so you have a few options.

 

Do ground floor in isolation with ASHP, but unlikely to get any grants, as you haven't covered upstairs heating demand. Add upstairs later when and if permitted development rules change to two units and they also allow cooling under permitted development.

 

Get your noise survey stuff done and press on with planning permission, sounds expensive and they may still say no.

 

Or change to something different, talk to other installers, there are plenty of water based ducted fan coil systems out there,to allow one outside unit.

 

 

[gamestrolley]

Stick one heat pump in a shed and one outside

[JohnMo]

3 minutes ago, gamestrolley said:

Stick one heat pump in a shed

What will achieve?

[Bancroft]

On 30/12/2025 at 08:37, SBMS said:

One heat pump outside (probably a 9kW would

work for you). Inside then we have UFH on ground floor and 7x wall mounted fan coils (one for each bedroom plus landings).

How well does this all work in practice?  At the moment I'm planning on separate ASHP and aircon systems for two reasons - one, not all eggs in one basket, and two, I've read elsewhere about a setup like yours that, although it does both jobs to an extent, is a compromise overall.

 

Interested to hear about your real life experience with such a system.

[JohnMo]

26 minutes ago, Bancroft said:

How well does this all work in practice?  At the moment I'm planning on separate ASHP and aircon systems for two reasons - one, not all eggs in one basket, and two, I've read elsewhere about a setup like yours that, although it does both jobs to an extent, is a compromise overall.

 

Interested to hear about your real life experience with such a system.

Only thing I would add, watch modulation levels especially at or around 7 to 10 degs. If you have a unit that doesn't modulate well at this temperature your overall SCoP will suffer. Even healthy cycling has a direct impact on achievable CoP, due to the impact of standby energy usage.  The lower the overall heat loss the bigger the impact on CoP.  So if you have a design heat loss of say 3kW at -3, you want a heat pump that at 7 degs has a min output of 1.5kW or lower, so it can tick away all day if it wants.

[SBMS]

3 hours ago, Bancroft said:

a compromise overall.

Why is it a compromise out of interest?

[Bancroft]

On 31/12/2025 at 14:30, SBMS said:

Why is it a compromise out of interest?

Only going on the experience of others but I have read others say that while dual systems can cool they are never able to get to the cooling temperatures that a 'proper'/dedicated aircon unit would be able to achieve.

 

If that assumption is incorrect, then great because that's what I'm looking for.  But, opinions seem to vary and I'm just trying to find ground truth.

[-rick-]

13 minutes ago, Bancroft said:

Only going on the experience of others but I have read others say that while dual systems can cool they are never able to get to the cooling temperatures that a 'proper'/dedicated aircon unit would be able to achieve.

 

ASHP + water fancoils can do the same as ASHP + refridgerant fancoils. ASHP + UFH cooling can't.

 

ASHP + water fancoils has the benefit that it can also do DHW heating but will, I believe, be marginally less efficient than a refridgerant system*. Most large offices and industrial sites will use water systems as refridgerant is expensive and hugely environmentally damaging if it leaks so it doesn't make sense in big buildings but is cheaper in small scale installations.

 

13 minutes ago, Bancroft said:

If that assumption is incorrect, then great because that's what I'm looking for.  But, opinions seem to vary and I'm just trying to find ground truth.

 

It is incorrect though more in understanding the context of when it's been said. I think you've mainly seen it said here in relation to systems that either don't want to go below dew point (to save extra effort in insulating all the pipes thoroughly) or because the system fed under floor systems that indeed can't compete with fancoils.

 

* Because of the restrictions on use of R290, it's possible (purely guessing) that a water based R290 system may well outperform an older R410 refridgerant system. Probably not a modern R32 system though.

Edited January 2 by -rick-

[JohnMo]

Think this all getting a little confused.

 

A2W, cooling via a fan coil at low flow temps, below condensation temperature, needs pipe insulation and it needs a condensate drain. A2A needs exactly the same.

 

A2W can use a fan coil, operated above condensation temp, which doesn't need insulation or condensate drains. A2A cannot work in this mode.

 

A2A generally doesn't do DHW (some can, but an expensive option). A2W does do DHW out the box.

 

Both A2A and A2W do heat and cool, but I'm not a fan of blown heating systems, don't find them comfortable.

 

UFH can heat and cool, cooling isn't the same as a fan coil. But takes the edge of the house nicely.

 

Fan coils are just like radiators need to be sized for the performance needed, at the flow temperature you specify.

[SBMS]

7 hours ago, Bancroft said:

Only going on the experience of others but I have read others say that while dual systems can cool they are never able to get to the cooling temperatures that a 'proper'/dedicated aircon unit would be able to achieve.

 

If that assumption is incorrect, then great because that's what I'm looking for.  But, opinions seem to vary and I'm just trying to find ground truth.

I think that assumption is incorrect. The unit we are installing for example produces water temperatures as low as 5deg C. Put across

a fancoil the outgoing air temp would be around 9-12 degrees. Traditional a2a fancoils produce 8-12 degrees chilled air so they are pretty much on par. 
 

This is notwithstanding others comments Yhat all pipes would need lagging to operate at this temp. But this is the same for a2a. An ASHP has the added benefit of slab cooling which is surprisingly effective because of

its mass; and can cool at higher temps of circa 16 Degrees (therefore obtaining a better cop).
 

This is the reason I went for the m series aquarea - It natively supports two zones to

keep UFH above dew point but allows ‘proper’

air con like cooling in bedrooms for really hot days. 

[BintyAndTheBeast]

Quick update.

 

we should have a quote arrive in coming days to install a new model Panasonic Aquarea [I think] M series unit which will have:

- air to water for underfloor heating and a couple of towel rails we are retaining;

- 2x 5 port fan units in our attic running ducted heating/cooling for all of upstairs

This has just been signed off by Panasonic so just getting pricing and a quote built.

 

johnmo - can I please thank you for planting the seed, and while I had effectively ruled it out, I am glad I spoke to Panasonic technical over the Christmas break who settled my mind initially that they would be able to out a system together.

 

this doesn’t resolve our outbuilding in the short term, but plan is to wait on the relaxing of permitted development rules to install a standalone unit in there. There was a choice to incorporate this into the Panasonic system we are installing but I had concerns that it would often likely be the only outlet calling for heat/cooling, so running a 9/12kw system to fulfill this would destroy COP/reduce the life of the unit.

 

I hope in a week or so to have signed off, subject to quote.