Split Air con

[tamzzy]

@tamzzy i think 10 or 11

I assume you or they have done the heating/cooling calculations.
You don't want to over-size the outdoor unit as this will cause short-cycling, potentially more expensive to run and also shortens the life-span of the outdoor unit.

Normally the outdoor unit is sized smaller than the total sum of the indoor units.
(For example mine is 6.8kw outdoor unit for a 7.5kw total combined indoor)

 

[Daaaavvveee]

Found a local company on Facebook, reviews on there back to 2022 and all seem good/genuine, pictures of the installs look neat. We're after a split system in 4 rooms, and I've been chatting to him, sending floorpans/pictures etc. He thinks ~£1500 per room, and is coming next week for a physical survey. My only slight concern is he appears to be a sole trader, with no companies house details etc, not sure how common this is or if it's worth being concerned about.

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I had an initial quote back from the same company….. same price….. hmmm

Let me know how your survey goes!

 

[RockLobster]

I assume you or they have done the heating/cooling calculations.
You don't want to over-size the outdoor unit as this will cause short-cycling, potentially more expensive to run and also shortens the life-span of the outdoor unit.

Normally the outdoor unit is sized smaller than the total sum of the indoor units.
(For example mine is 6.8kw outdoor unit for a 7.5kw total combined indoor)

I'll be honest I'm pretty disillusioned with the whole process. First guy completely dismissed my idea of having a unit on the landing. He was quoting £5.5k for three Mitsubishi Heavy Units (5k - kitchen, 2.5k bedroom (behind door not where I wanted) and 2.5k main living room). 7 year warranty and a good brand. I know Daikin are good but the price does seem expensive. The second quote I had a single text message which was what I put in an earlier post. No mention of brand and model, no mention of warranty or what size outdoor unit. Looking at Daikin's website you only get 5 or 7 if they are Daikin certified otherwise it's 2 years so 2 years. Also he didn't mention what condensate pump he would install. Second guy did a rough estimate based on room size, no heat loss calculations, etc.

I've been debating a number of options. Do I go back to the first guy and try to convince him that a landing unit may work based on what I've read and seen on YouTube. Do I just have one or two units downstairs and have portables upstairs or do I just scrap the whole idea and use portables.

 

[tamzzy]

@RockLobster MHI is 3 year warranty IIRC
Daikin is 3 years if installed by a non-certified installer, 5 years if they are certified, 7 years of they are a premiere installer.

You are paying a lot because of the outdoor unit. Daikin 10/11kw outdoor units are expensive!

Landing unit is only viable if you keep all the doors open all the time...so I can see why #1 dismissed the idea.

But tbh, they are there to install the system you spec, so just go back to him and ask for a quote for a system you want - this was the route I took with the installers.

 

[throwaway4372]

I haz AC!
For reference it was £6k ish for 3 way split.
Mitsubishi, 10 yr warranty assuming I service it every year, which I will.

 

[DampCat]

My contacted installer has offered Ducted AC. I fear it's because I've only asked to do upstairs, and it would be quicker.

My loft is boarded but it's quite full. Would I have to worry about noise from the unit reverberating through the joists?

Edit: on the surface of it I quite like the idea of not having a big unit in the kids bedrooms. But what if eventually I do want to expand to doing downstairs?

 

[Trifid]

My contacted installer has offered Ducted AC. I fear it's because I've only asked to do upstairs, and it would be quicker.

My loft is boarded but it's quite full. Would I have to worry about noise from the unit reverberating through the joists?

Edit: on the surface of it I quite like the idea of not having a big unit in the kids bedrooms. But what if eventually I do want to expand to doing downstairs?

I would want ducted from my loft, but I generally thought installers were less interested in doing it? Something to consider is, how are they getting the loft unit in? They are rather big...

Downstairs is normally split units, unless you want a big expense of installing ducts throughout.

 

[~Divine~Wind~]

I was looking at a split unit at each of of the house, both 3 way splits serving 3 individual rooms.
Doing it in this way would mean I dont need cabling/Piping running the width of the house, anyone got similar?

Hopefully would then also mean that when we eventually get solar sorted can use them to heat/cool the individual rooms we use most when needed.

 

[tamzzy]

I was looking at a split unit at each of of the house, both 3 way splits serving 3 individual rooms.
Doing it in this way would mean I dont need cabling/Piping running the width of the house, anyone got similar?

6 rooms to cool? presumably you live in a detached mansion so having two external units is permissible
(only allowed to have one external unit if you live in a semi-detached)

piping running in the loft for the width of the house isn't too bad. all external units have max permissible runs that would be well in excess of required (for example, my daikin external unit allows a 60m run total system run, with a max single run of 25m)

 

[montymint]

I was looking at a split unit at each of of the house, both 3 way splits serving 3 individual rooms.
Doing it in this way would mean I dont need cabling/Piping running the width of the house, anyone got similar?

Hopefully would then also mean that when we eventually get solar sorted can use them to heat/cool the individual rooms we use most when needed.

I’ve got split aircon , bedroom and affixe and the piping goes across the loft, but it’s not all that bad to be fair. It’s just inside some of the trunking used outside

 

[Mason-]

My contacted installer has offered Ducted AC. I fear it's because I've only asked to do upstairs, and it would be quicker.

My loft is boarded but it's quite full. Would I have to worry about noise from the unit reverberating through the joists?

Edit: on the surface of it I quite like the idea of not having a big unit in the kids bedrooms. But what if eventually I do want to expand to doing downstairs?

No not if it’s installed ‘normally’ they hang threaded rod from the rafters and mount it on that. So it’s not in direct contact via the joists as it’s mounted to the rafters. They should then use insulated solid ducting for most of the route to your outlets, and the last part they change it to an ‘acoustic’ ducting which is essentially flexible ducting. That way any vibration going through the solid ducting doesn’t transfer to your ceiling.

 

[Junglist]

Had the first of 3 installers around today to get priced up. Though I've been advised it's usually around £1500 per room. We had our loft boarded out earlier in the year which now seems like it was a lucky coincidence as it was one of the first few questions we got asked when he was on site.

Budgeted for up to £8k but hoping it's under that by a decent amount.

 

[NotAGolf]

I would want ducted from my loft, but I generally thought installers were less interested in doing it? Something to consider is, how are they getting the loft unit in? They are rather big...

How big are we talking? If the unit is that big, presumably weight becomes a potential issue too?


I'd quite like a ducted system, and I'm doing some renovations so could easily create a fat fake wall on the landing to be able to run a pipe downstairs. If I use posi joists, then hopefully I should be able to run some ducting fairly easily. Not sure if the webbing will be big enough though.

 

[Trifid]

How big are we talking? If the unit is that big, presumably weight becomes a potential issue too?

Can look it up, i.e. this one is 240 x 1,400 x 700.

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then add a plenum and ducts for inside the loft.

 

[Pawnless Endgame]

I've gone through the first 100 posts on this thread and planning permission seems indecisive. Stafford Borough Council couldn't advise me either and said it's best to complete a Certificate of Lawfulness of Proposed Use or Development (LDCPP). Their responses were canned though and thought I was building an extension! It seems a bit much though considering that a new kitchen or bathroom is a bigger project and doesn't need planning.

PDF link - https://ecab.planningportal.co.uk/uploads/appPDF/Y3425Form001_england_en.pdf

I tick the usual boxes e.g. it's a freehold, needs to be a house (not a flat), it's not a listed building, it's not in a conservation area and the outside half of the system mustn't be visible from the road or bigger than 60cm³. What I'm unsure of in my research is that the system should be 'reversible' so to provide heating as well as cooling.

Does the outside half of the system make any noise?

Things that I'm unsure of on the form:

"Agent name and address" - is that the provider that I'm going to use? I don't know who I will be using yet. Alternatively, if I found a provider (agent), would they complete the form on my behalf?

Has the work already started? (tick yes or no). I don't know why I would risk starting the works if I don't yet have permission. Would I risk police action if I later failed planning or is it a civil matter?

Then it asks what materials I will be using e.g. walls, roof, windows, doors, lighting etc. Either this isn't relevant as it's not building works, or if it is relevant, I won't know what the materials are until the fitters send me a quote. The form does seem very much geared towards building an extension.

 

[Scuzi]

I've gone through the first 100 posts on this thread and planning permission seems indecisive. Stafford Borough Council couldn't advise me either and said it's best to complete a Certificate of Lawfulness of Proposed Use or Development (LDCPP). Their responses were canned though and thought I was building an extension! It seems a bit much though considering that a new kitchen or bathroom is a bigger project and doesn't need planning.

PDF link - https://ecab.planningportal.co.uk/uploads/appPDF/Y3425Form001_england_en.pdf

I tick the usual boxes e.g. it's a freehold, needs to be a house (not a flat), it's not a listed building, it's not in a conservation area and the outside half of the system mustn't be visible from the road or bigger than 60cm³. What I'm unsure of in my research is that the system should be 'reversible' so to provide heating as well as cooling.

Does the outside half of the system make any noise?

Air source heat pumps can be installed under Permitted Development rights as long as they meet certain criteria, and also the MCS020a standard. The MCS020a standard is a noise calculation based upon the documented peak noise output of the external unit and other factors related to teh position of the unit relative to a reference point which is 1m perpendicular to the nearest habitable room of a neighbouring property e.g. living room or bedroom, not a hall. If you have the model of the external unit and can provide some photos & measurements of where it will be placed relative to the neighbours, we can probably help you.

--------------------------------
As of September 2026, an air-source heat pump (ASHP) in England can generally be installed under Class G, Part 14 permitted development if all of these apply

• Domestic property: on a dwellinghouse/block of flats or within its curtilage.
• MCS 020a: the installation must comply with the Microgeneration Certification Scheme Planning Standard MCS 020a (the sole permitted certification scheme from 28 May 2026).
• Size: outdoor unit, including housing, must be no more than 1.5 m³ for a house or 0.6 m³ for a block of flats.
• Number: normally 1 ASHP for a non-detached house or block of flats; up to 2 for a detached house.
• No wind turbine: there must not already be a wind turbine on the building or within its curtilage.
• Roof: installation on a pitched roof is not permitted development. On a flat roof, every part must be at least 1 m from the roof edge.
• Listed buildings / scheduled monuments: PD does not apply within the curtilage of a listed building or on a scheduled monument site.
• Conservation areas / World Heritage Sites: additional restrictions apply to positioning relative to highways.
• Other locations: on a wall facing a highway, the unit cannot be above the ground-floor storey.
• Noise: it must satisfy the applicable MCS 020a noise calculation/limit.
• Siting: as far as practicable, position it to minimise visual impact and impact on the area's amenity.
• Cooling is allowed: following the 2025 changes, the system can provide heating and cooling; it cannot be used solely for cooling.
• PD rights must still exist: check that they haven't been removed by an Article 4 Direction, planning condition or other restriction.
• Building Regulations still apply: permitted development is only about planning permission; it does not remove Building Regulations or other statutory requirements.

------------------------------------

Things that I'm unsure of on the form:

"Agent name and address" - is that the provider that I'm going to use? I don't know who I will be using yet. Alternatively, if I found a provider (agent), would they complete the form on my behalf?

Has the work already started? (tick yes or no). I don't know why I would risk starting the works if I don't yet have permission. Would I risk police action if I later failed planning or is it a civil matter?

Then it asks what materials I will be using e.g. walls, roof, windows, doors, lighting etc. Either this isn't relevant as it's not building works, or if it is relevant, I won't know what the materials are until the fitters send me a quote. The form does seem very much geared towards building an extension.

Getting a Lawful Development Certificate will help but it's at least an 8 week long process and can bring a lot of headaches you won't want if you have a load of NIMBYs around you. If you meet all of the above requirements you're golden.

Ask any potential installer if the install will meet MCS020a requirements. IF they know what they're talking about they will provide you with everything you need.

If your install was non-compliant with PD, the worst that could happen is that the local authority could issue an enforcement notice ordering you to take it down.


Edit..
Long story short, I instructed what I thought was a well reputed local firm to install air conditioning for me. It wasn't until a neighbour complained to the council that I learned about MCS020a. Mine wasn't compliant and I'm in the process of amending the install to become compliant. Fortuunately the installer is standing by their word to make it right, but a parts shortage means a 6 month wait. It was a steep learning curve but I got very familiar with all of this very quickly! The local planning enforcement team are being quite reasonable actually.

 

[tamzzy]

@Pawnless Endgame , what @Scuzi said. it falls under permitted development as long as the criteria are met.
main thing is the sound levels. explanation here: https://mcscertified.com/wp-content/uploads/2025/07/MCS-020-a-Issue-1.0-Final.pdf
calculator here: https://mcscertified.com/?standard=mcs-020-a-calculation-tool
(easy to do your own calcs...just plug the numbers in)

this is mine, for example:

 

[DampCat]

Our guy has said the ducted system would require 85cm of clearance to get into the loft which we don't have, and I don't think I'm willing to modify the hatch as well as do the install. We already have a lot of work going on.

Hes quoted Mitsubishi LN 2.5k X4 for 8.5k which I will consider (there's actually about 15 options between 6k and 9k which is almost too much choice honestly).

 

[Junglist]

£5800 for a Mitsubishi Heavy Industries Premium 8kW multi-split across 4 rooms.

Only thing I'm concerned about is that it has black trunking and the living room which sits at the front of the house would need to go out the front and around the back. Issue is we have a white 'cottage inspired' property and it may stick out like a sore thumb.

 

[Simon D]

£5800 for a Mitsubishi Heavy Industries Premium 8kW multi-split across 4 rooms.

Only thing I'm concerned about is that it has black trunking and the living room which sits at the front of the house would need to go out the front and around the back. Issue is we have a white 'cottage inspired' property and it may stick out like a sore thumb.

You can get the trunking in white

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