@editor Yes, plastic reusable filters than need cleaning maybe monthly subject to how much you use it and how dusty your home is. This is very easy though.

@editor I do have to say though, I think nearly everyone that works for me have them though, as they get them for cost if they are staff, so its not a chalk and cheese thing its more I am not allowed one in my house due to the way they look and my home is perfectly insulated and slightly shaded that when outside is 34 my kitchen is 26 and my living room 24, so i do manage somehow to keep the building cool or cool enough I have never needed to charge to the office and chuck one in over a weekend, we also live 165m above sea level at the very top of a hill overlooking the channel so we often get the sea breeze which probably helps a lot.

Also, I have a fully air conditioned office 3 miles from my home so I can go there when it 40 Deg C.

@ashp-bobba good advice and thoughts. It depends what the customer is really looking for and their circumstances. A2A will always be cheaper to install with more variations. A2W is often great with UFH but slow to work and no real cooling option.  We've just installed to a church, A2A and also infra red panels as that was the best solution. Another church wanted UFH to to toilet and kitchen areas so again a great option.

@ashp-bobba Brilliant, sounds great

@ashp-bobba interesting insights. We also chatted after our podcast recording yesterday (it was on maintenance and servicing if anyone’s interested) and I was genuinely surprised how many A2A systems you fit in domestic properties for heating. I thought the A2A market in the UK would be purely commercial/retail.

@editor Something changed in this last 12 months, they seemed to be a higher demand, although I think the interest is more cooling led, there is a strong selling point for heating. Multi splits seemed to be very popular this year where a home owner can have 3, 4 or even 5 units off one external unit to cover a large amount of areas in the home.

I'm seriously considering an air to air A2A multi-split system in my well insulated 2 bed terrace as a way to get disconnected from the gas mains. I'm in West Yorkshire.

It seems to me A2A has a couple of significant efficiency advantages. By using the heat pump output directly into the room you are always working into the lowest temperature in the system. Typically 21 C though in my case 18. In an air to water A2W system the heat pump heats the water flowing in the emitters. This always has to be warmer than the room of course, and is at it's warmest and so least efficient when demand is highest. The world of A2A seems less concerned about SCOP than A2W but I have seen reliable figures that a SCOP of 5 or 6 is easily achieved. Does anyone know more about that, or of any sources of information?

The second difference is that the thermal mass and low flow temperature of A2W means the spare power to change the temperature of any room is low. Which means the advantages of zoning and set backs (lowering the temperature when not needed) are not available (or at least not worth the loss of COP). In my circumstances I've used both to great effect bringing my annual gas use to around 3,200 kWh.

Naturally I am concerned how to design a system for best comfort. It seems to me floor mounted units (consoles?) have advantages there. I'm struggling to find much information about them.

I would also be interested in what to look out for to find a good installer.

Here is a screenshot of a spreadsheet I picked up somewhere to give you an idea of SCOPs. We have an A2A in our kitchen and it works well, particulalry in places that dont have to be heated all of the time.

@springswood we install these nationwide and I have them in my own home. 
they are super efficient (nothing cheaper) and cost effective to purchase. The only disadvantage with the floor units is they are quite large, double the size of high wall mounts.

@bontwoody Thanks for the info. Quite a spread of values. I was also wondering if anyone had actually measured the performance of their system.

@dgclimatecontrol. Size is obviously relative. For instance in my living room, where I favour a floor mounted unit, the Heat Geek survey I had for A2W specified a three panel radiator 600 mm high and 1800 mm long.

Good point, I only know about heatpumpmonitor, which focuses on ASHP even if it covers some GSHP. 

Would there be anything similar for A2A? 

This is an interesting post and a breakdown analysis of heat pump types where it’s really cold ie the Nordic regions

https://www.carbonbrief.org/guest-post-how-heat-pumps-became-a-nordic-success-story/