@ltron2, welcome to the forums.

A2A isn’t an area I know a huge amount about, and I’m hoping to record a podcast episode with @ashp-bobba this week to address some of the shortcomings in my own knowledge, and probably that of many consumers in the UK. That said, I’ve had a look at this and there are a couple of things I’d want explained before going any further if I were you.

The first is the sizing. I wouldn’t simply add four 2.5kW indoor units together and conclude that you’ve been given a 10kW heating requirement, because multi-split A2A systems don’t work quite that neatly as far as I know. But a 10kW outdoor unit for a 61m2 maisonette, combined with your relatively low annual gas consumption, certainly looks large enough to make me ask some questions.

I’d want the proper survey to establish what the flat actually loses on a cold day, and then ask them to explain why this particular outdoor unit and four indoor units have been chosen.

The price also feels fairly punchy to me. £7,400 isn’t so far outside current multi-split pricing that I’d call it outrageous, but for a small 61m2 property, with no apparent ductwork, one outdoor unit and four conventional indoor units, I certainly wouldn’t assume it represents good value without getting a couple of competing quotes.

Please keep this thread updated when they come back to you, because A2A is becoming increasingly interesting for UK homes and it would be useful to see how one of these Octopus Trusted Partner proposals develops from an initial estimate into an actual design.

So, if they are keeping within the rules to eventually get you the A2A Grant they will need to place an indoor unit in every habitable room, so living, bedrooms and dinning for example 'hallways, bathrooms and Kitchen need to have the heat-losses covered but not necessarily have an indoor unit if it will not fit. So 1st rule is to calculate the whole house heating demand / losses, that will be the capacity of the system you will need to cover, next issue is most manufacturers smallest internal unit is a 2kW indoor but they can be design against a lower external and used at a lower capacity. For example 4No 2kw's can go on a 6.8kW external multi and so on.

From what your energy use is I would say you are closer to 3kw heat loss but if they were to design it for cooling and you asked for this then they would have allowed 90w/m2 cooling or higher rather than 49w/m2 heating. All buildings gain heat from solar as well as loose heat in the winter when there is a lack of solar, often the AC is designed to fight heat gain and solar gain, your peak heat loss in winter may be 3000W but your peak summer is likely 5500w or higher subject the glazing and fabric make up.

Basically you need a full heat loss done to obtain a correct design.

On the price, the average cost of fitting this tech is around £1500 - £1700 for a single split and can be £1700-£1800 for a multi split per room and can be higher for the larger units, the price is correct for a 10kW external with 4No 2.5kW internal units if thats what you go with.

I don't think the AC or A2A grant suits 90% of the dwellings in the UK as a solution for heating only but if you are willing to pay it is the best solution if you desire both heating and correct meaningful and effective cooling. By designing for cooling it makes the cost more expensive as the cooling is almost always double the heating demand just because we love glass and don't use things like external shutters or other useful solar deflecting tech such as solar deflecting glass or smooth white houses. 

I am sure the A2A grant if ever its able to be used, is designed for flats and very very small homes with no more than 2 or 3 rooms otherwise its not cost effective to have so many internal units if you follow the rules to the letter.

IMHO the A2A grant muddied the waters a bit as since the announcement I have had to explain to 80% of customers interested in A2W but they drift to "if I have A2A I get cooling" that the A2A grant is not claimable just yet, the A2A will end up more expensive in your 7 or 8 room home and they do not make a system over 6 units on a multi so you have to have multiple units to cover all of the habitable rooms or a multi ducted system in the lost to cover all the bedrooms and they can be £6,000 - £8,000 due to extensive ducting "when done correctly" before you even do the ground floor. 

I hope the above helps and explains the costs for you.

@editor Hi Mars, thank you so much for your thoughts and for welcoming me, it's good to know that you agree that there are questions to answer.  I will certainly keep you all updated and I definitely intend to get them to do a proper survey.

I'm really glad that I found this community (I thought I'd ask the experts) through watching your video with Tom Bray today and what you said about the importance of getting it right resonated with me.

I've also found your Heat Pump Quote Review Service which is a great idea and I'll make use of it once I get a proper quote following the survey.

@ltron2 Please do keep us updated as you move along and progress. I would be interested to hear the outcome after they survey if they do.

@ashp-bobba Thank you, that's really detailed.  I had no idea that those were the requirements and yes I did ask for cooling (which is the main bonus of A2A).  As I see it I have basically three habitable rooms in a first floor maisonette (the living room, office/piano room and bedroom).  I have a very small lobby downstairs but that's just my entrance off the street. The kitchen and living room are basically one long room separated by a door and of course I have a bathroom of a decent/average size with the boiler in the bathroom airing cupboard.  You go up the stairs from the lobby onto the landing and that's how you traverse the flat (with rooms on either side and the living room at the far end).  I don't know whether my definition of a habitable room matches theirs but that's how I see it.

Could I narrow things down and reduce costs for cooling by emphasising further that I only really need it to be strong in one room or two at most (bedroom and living room)?  If the rules are around heating perhaps there is more flexibility in terms of cooling which would enable me to reduce costs.  Obviously I talk about cost, but I very much want to avoid undersizing.  A reasonable amount of oversizing is fine and probably a very good idea, I just don't want far more than I need.

@ltron2 where are based? You might be lucky and be in Simon’s installation area… he’s one of the best installers in the country.

@editor I am in Cardiff, that would be great if so.

@ltron2 I’m afraid @ashp-bobba is not near you (he’s in Kent), and our installer list in south Wales is beyond limited.

@editor That's a pity, but thank you for checking.  I'll let you know what IR Energy (my Octopus trusted partner) say.

@ltron2 

We currently have a gas boiler for hot water and central heating complemented by an Air-to-Air (A2A) system that provides very efficient heating and cooling. See this thread for details: https://renewableheatinghub.co.uk/forums/air-to-air-heat-pumps-air-conditioning/what-air-to-air-air-conditioning-system-do-you-have-and-how-efficient-is-it-on-heating-and-cooling/

Substantial amounts of insulation and a new gas boiler reduced our annual gas consumption from 21,000 units down to 14,400 units. Adding A2A has taken it down to just 8,000 units - 40% of what it was originally. We have just two A2A indoor units (3.5kW and 2.5kW) in a 146 sqm 4-bed detached (12 rooms in all), but they are nevertheless more than sufficient to keep the whole house cool on the hottest days of the year. Running on cheap rate overnight electricity at over 500% efficiency gave us a substantial amount of heating at less than 2p per kWh last winter.

I've done a deep analysis of costs and concluded that there is now no economic argument and only a very weak environmental one to replace my gas boiler with an Air-to-water (A2W) heat pump - see: https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/analysis-of-the-economics-of-switching-to-an-a2w-ashp-compared-to-other-heat-sources

I suggest that you consider paying for an A2A system yourself. You can then specify only what you need - possible just one or two indoor units - and keep the costs down. As @ashp-bobba notes this will likely be roughly £3500 for a multi-split with two indoor units or £1700 for a single-split system with one indoor unit, which maybe all that you really need.

Your gas usage is already very low thanks to your excellent insulation, triple glazing etc., so it is likely that you can meet a very significant percentage of your heating requirements using just one or two A2A units, and use gas for little more than hot water heating. Your carbon footprint for that will be very small, and an A2W heat pump would only have efficiency of around 170% for hot water heating anyway, so would potentially only increase your costs.

With A2A you could end up with a system that cools efficiently, heats efficiently, significantly reduces your heating bill and your green house gas emissions, and has very useful redundancy. If the gas boiler stops working for some reason, you can heat the whole house reasonably effectively with the A2A, and vice-versa. 

@rob-of-york Thank you, that's really useful information and it is definitely a worthwhile option if I can't get good value for money for a full replacement (which is my preference).

I am impressed that your relatively small A2A system manages to heat and cool your property so well.  What EPC rating does your home have and do you have triple glazing (I know you've got good insulation)?  What's the wattage on the external unit and what brand is it?

I still haven't heard anything from IR Energy, perhaps they did not like me questioning their quote (in the meantime I am looking at other companies).  I will push them if I don't hear something soon.

By the way, I am not currently looking at A2W because I suspect the external unit if ground mounted would be more difficult to get freeholder permission for (communal grounds) and I would miss out on superior cooling.  For a maisonette of 61m² I feel A2A makes more sense anyway and that £2500 grant should be coming online in the relatively near future.  I have to do an asbestos survey and electrical work including full replacement of my inadequate fusebox before I am able to get the heatpump anyway.  For now I'm getting quotes and considering my options.

There is also a 0% loan scheme for green upgrades provided by the Welsh Government which you can pay back over up to 10 years which I am looking into (they also do their own independent survey):

https://developmentbank.wales/green-homes-wales