Air-to-air vs. air-to-water heat pumps - why we chose A2A

If you're thinking of replacing your gas central heating with a heat pump system then you probably already know about air-to-water heat pumps but may not have considered air-to-air (otherwise known as air conditioning) as an option. In this video I'll explain why we decided to get an air-to-air heat pump heating system installed and run through a few of the pros and cons of that system compared to the more common air-to-water heat pump heating systems that are typically talked about.
00:00 Introduction
01:25 Pros and cons
16:27 Why we chose air-to-air
Please note that Tim is not a professional consultant, just an enthusiastic amateur, so cannot reply to requests for advice or opinions on specific systems or green investment opportunities. Thank you for your understanding.
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[@jbtl1130]

We have both an a2a and an a2w system installed. Of course it is good to compare each system, but I found them to be largely equivalent. It just depends on personal preferences and existing setup which one is best suited. The biggest improvement is going to be when you compare to a current gas (or oil] boiler. Running and climate costs are just so much lower with any type of heat pump. In our situation, the a2w covers heating demand for most of the heating season. The a2a gets us through the coldest and hottest days, and allows the a2w heat pump to run more efficiently through the reamining days of the heating season. In time, you might want to consider a small a2w heat pump (which Im conviced will get very cheap within a couple of years] for the wet areas, the other two rooms + hot water. Best of both worlds really.

[@100uo]

Great video. Another big benefit is that you can do a2a in chunks, i.e. room by room, without having to do the whole house. For example I just put one a2a in my kitchen/dining for 1.5k last year, and it's been brilliant. That room was cold in winter and hot in summer, and the a2a solved this. I am still keeping my gas boiler for the foreseeable future.

[@TimAndKatsGreenWalk]

Yes, that's a good point. Glad it worked for you in this situation.

[@rover-t]

I've had split air conditioner units in all my homes in Asia over 24 years. They are excellent. Fan noise is so minimal, unit is high on the wall out of the way, the thermal dynamic of cooling the air is rapid. Our latest units are all controlled by an app on my phone. An A2A heat pump is the same as my air conditioner here, but with heat as well, so it's a great option. Cost of installation and ongoing use is as good as central air. As a Brit I've lived with the expense and inefficiency of radiators which are tractor engineering in comparison. A2A is the option I will go with when I build a new home in the Pacific N West in the next few years.

[@SuperDiagnostic]

Great comparison, great video.. can't wait for your cost comparison after hearing some of the recent forum comments... ThnX

[@TimAndKatsGreenWalk]

Yup, lots of stats to go through. Should be fun!

[@colingoode3702]

Like you said Tim, the biggest pro of an A2Air system is the facility to have cooling in the summer from the same system. The trend for more Home Working has seen a big increase in single room A2Air AC systems installed in domestic houses & garden rooms. These provide the same heat/cool facility that people may have had previously when they worked in a central office or similar place of work &, the AC they now have in the cars they drive. Moving that concept on further to a whole house A2Air heating / cooling system is a natural progression. Multiple multi-systems (like yours) or, a single 2-pipe VRF type system with up to 8 indoor units on a single outdoor unit running off of a 240v/1ph/50hz power supply, are valid alternatives for domestic house installations. Both of these system types are also installed in commercial buildings & have been around for many years. Hot water heating can be accommodated by some makes of Multi / VRF systems but having "all your eggs in one basket / system" is maybe not the best policy, which is why having a solar diverter or a Heat Pump cylinder to do the hot water independently is I think a better idea. Looking forward to the next vid & the stats.

[@waqasahmed939]

I'm considering that too, especially as I'd have to realistically replace my radiators and piping any way I also currently have excess power from just a 3kw solar system , even in April.. I've provisionally been allowed six more panels, which means I'd have even more excess power An AC then would either cost me £0 or very little in the summer. So it's very tempting

[@boyandbelugee]

Thank you for this informative video as we are considering the heat pump.

[@mikerushton3266]

Hi Tim. Very interesting videos on the A2A system. My house appears similar to your in layout and I’ve just had a quote for 2 indoor units downstairs off 1 outdoor unit. At approx. £4500 for the 2 mid range Mitsubishi wall units it seems expensive compared to your install. Looks like u got a great price as your units are really cool.

[@markw1590]

Thanks for the video, looking forward to the energy costs. Also could you tell us the maintenance costs as well. Really good video series. Fully agree with the cooling part in the summer it's only going to get worse unfortunately.

[@TimAndKatsGreenWalk]

Yup, I'll try to remember to mention maintenance costs, that's a good point.

[@normanbiggar]

Tim, 8:40 That’s more than 2 inches across. Great video and keep up the good work.

[@TimAndKatsGreenWalk]

The core samples that came out of the wall are 5.5 cm diameter, so close enough.

[@ChrisJakins]

We have the same setup here, and for the same reasons. I agree with everything you've said. Often A2A is criticised as being less comfortable due to the increased air movement. In very cold conditions this can be a slight issue, but not a deal breaker. I do find the heat in the room tends to fill up from the top down, as it would for any heating system but quite noticeably so with high level air handlers. Our running costs seem to be roughly on a par with gas on the old pre-crisis tariffs, but looking ahead I can only see it working out as the cheaper option averaging out over the year. We have all been conditioned to see gas as the cheapest and most reliable heat, but I think those days may be gone, or at least on the way out. The future is about conserving energy. Obviously this video is not about comparing installation costs of boilers with heat pumps. We all can appreciate that sticking in a combi boiler is less capital up front. That is a big challenge for the wider population, how to make heat pumps a no brainer. Things are moving in that direction.

[@TimAndKatsGreenWalk]

We direct the vents directly downwards on low fan and that results in very little noticeable air movement and a comfortable even heat, so that seems to be working well. We've also found the running costs to be similar to gas and I've got a full breakdown of all of that planned for a future video. Eventually heat pumps will become the default installation for new build homes so that should help normalise it a bit more too hopefully, and bring down the costs. Step by step.

[@petanders1968]

Tim Great video again on this subject. One point worth bringing up is annual maintenance like what you would do for a gas boiler where you would ask your local gas professional to service the boiler. In our case we have 3 A2A units and reading through the user manual it says one should get the units refrigerant checked by a professional annually so that is another cost to include in the scenario. We haven't had our units serviced yet we have had them for around 16 mths now and all are working fine but it is something that we will be organising sometime soon, up to now we have cleaned the filters in each which is an easy job and not time depleting. Peter

[@adamcole4808]

Maintenance is pretty minimal. Refrigerant does not as a substance need to be checked/serviced/changed (anyone ever service a fridge?), although you can check pressures in the world of refrigeration these are VERY small system so not normal to check them periodically. They are sealed systems so unless there is a leak nothing should change. If you have a leak the system will stop on low pressure and then you need a repair but normally these systems go many many years. In Spain about half the household have these and I can promise you none are ever serviced unless they fail which is amazingly rarely. On the external unit its more visual check and noise, does it sound/look normal and is their no build up of debris. Every year the condenser (the fins) should be cleaned which is a easy DIY job. On the internal units I clean my filters usually twice a year and spray coil cleaner/disinfectant on the internal coils (again the fins). Hope this helps.

[@TimAndKatsGreenWalk]

Yup, I'll try to cover maintenance costs in the follow-up video too.

[@mahlercat]

Hello Tim, just to say the engineers are arriving today to install my air to air heat pump system. When I saw your video some months ago it finally made my mind up not to continue with a wet system and to go with this. Warm in winter, cool in summer and no more radiators and pipes. Crossing fingers it will be as good as the reviews and data say. Thank you Jon

[@TimAndKatsGreenWalk]

Nice! I hope it works out well for you. No complaints from us so far. I'm currently considering whether to add a heat pump hot water cylinder or not. Possibly next year.

[@nickieredshaw7835]

Thanks for a great video we’re looking at a heat pump of some description

[@simonchetwynd]

Thank you for sharing your experience. We have someone coming round to give us a quote in 2 weeks. Doing a step by step approach in that we still intend to use gas for winter and the air to air for spring and autumn so don’t have to heat all the radiators for and in the morning and evening. Cooling is worth its weight in gold for 1-2 weeks per year in main bedroom (we use cheap and nasty portable unit with pipe hanging out the window). Already have electric immersion for hot water with diverter from excess solar. IR panel to go in bathroom. If we get on well with it we’ll put air to air in other rooms and bin the gas entirely. A definite pro is you can quite easily incrementally add to a system.

[@TimAndKatsGreenWalk]

Yup, sounds like a good plan. Best of luck with it all.

[@richardlincoln886]

One of the big advantages of A2A is you can phase the install. Plan it up front - but phase in various rooms as you phase out radiators. No huge commitment to switch the whole building over in one go to a new' for the user ' technology. The fast heatup is useful too - its more like working with gas/oil heating - i.e. can be left off overnight for quietness, then takes 20 minutes to heat (at least my 2x rooms) pulling about 500watts when outside is over 5º, max 1.5kW if its nearer 0. Turn on with heat demand - rather than the A2W leave on and trickle heat. Hot water is interesting - combined tank/hot water air pumps are available and look interesting.

[@TimAndKatsGreenWalk]

Yup, all good points. Although we tend to leave ours on tick-over during most of the day to keep the walls warm (plus I work from home so need the heating on in any case) and then turn off overnight. I'm considering a heat pump hot water cylinder as a nice complement to the A2A heating.

[@chrisjones6542]

Great video, Like you are house (an old badly insulated (working in that) cottage) is full of micro bore pipe… I have (so far) installed 2 air to air units. 1 in the kitchen and 1 in the lounge to suck it and see, but kept the oil central heating. Until this very cold weather the air to air systems have been enough on their own… but in these sub zero temperatures the boiler has been firing up… the hope is I will use 1/2 the oil I used last year… I’m going to insulate as much as I can then put some more air to airs in the bedrooms THEN remove the oil…it’s a 5 year plan probably!

[@TimAndKatsGreenWalk]

It's a good plan. Best of luck with your upgrades!

[@mariusm3595]

You can use air to water same way with wall mounted fan coils. The advantage is that you wont have any refrigerant in the occupied space.

[@KevinLyda]

I live in Ireland and went with an A2W. However one end of my house always is a bit cold in winter for a number of reasons without putting down a fire. So I'm actually considering putting in a small A2A in this part of my house. And the cooling effect - while not often needed - is nice. The other option I'm looking at is infrared panels.

[@TimAndKatsGreenWalk]

Yeah, sounds like a good plan. I don't have experience with IR panels but a heat pump of any kind will always be more efficient in terms of converting electrical energy to heat energy, so I'd pick that over IR panels, personally. But I expect IR panels are cheaper to install.

[@Muppetkeeper]

I hope that you go for air to air. Infra red don’t really heat the substance of the house unless on for a long time, and obviously they are only 100% efficient, whereas a good air to air can be 500%, and will also heat the substance better.

[@peteg8920]

We have had A2A heat pumps in Sweden for many years. The difference here being that many houses are open plan so often one unit is sufficient for a normal sized house. I have a high wall unit installed under a window as I find it more comfortable to allow the heat to rise from floor level.

[@CaptainProton1]

Moved into a very damp 1980;s 2,000 sq ft bungalow surrounded by water and rising damp, Ripped out all the radiators and boiler and replaced with 2 x Heat Pumps and 5 x Air Conditioners. Took out the immersion heater and replaced it with a Sunamp the largest one they do. At the moment we are charging the Sunamp with cheap rate electric at night, it manages 2 to 3 very big full baths and all the washing up etc. 32 x 400 w solar panels and 2 x 17kwh batteries to offset the insane electricity costs and a further 10 x 450w panels to charge the car. The Air conditioning heats up very fast but we had huge humidity at 89%. Turns out the previous owners blocked all the roof breathing vents with insane amount of rockwool which is all covered in damp. Moved that and freed up the air flow....then installed a Positive Pressure Ventilation system. That bought humidity down to 72% but the had to build 150m of French drain as we had 2ft of sitting water as someone thought it was a good idea to fit a water proof membrain around the house to stop the weeds from growing!!! Now we are at 55% and the air conditioning is working way less hard than before. But radiators...i hate them. Sunamp works and only loses a little bit of thermal compared to immersion tank and half the size for twice the storage. Currently at 20 Deg C in House and using a total of 900w of electric in Dec.

[@TimAndKatsGreenWalk]

Very nice. That's a heck of a journey, but I'm glad it's working out for you now.

[@SarahMould]

Thank you so much for doing this - I have A2A scheduled for installation next spring in half the house, and your info has been very helpful. Going for Mitsubishi units as recommended by Graham (the famous installer from Gorleston), who will be doing the work.Haori units would have cost at leat £1k more! I'm approaching this as an experiment. If all goes well, will be doing the other half of the house the following year. At that point I'm hoping there will be better options for replacing the gas combi boiler for instant hot water.

[@TimAndKatsGreenWalk]

I'm glad I could help. I'm assuming that you don't have room for a cylinder, since you're after instant hot water. If that's the case you could search for electric boilers, as there are quite a few available that do that. If you do have room for a cylinder you might find this video helpful: kzbin.info/www/bejne/fZSzYaZjlpeFjNUsi=K__RbZNg-dR3rhLM

[@SarahMould]

@@TimAndKatsGreenWalk Thank you, yes - watched that too. I'm less concerned than you about getting rid of gas in the short term, so will probably wait until the fairly new boiler dies. Of course, having been encouraged to move from a cylinder to a combi boiler 20 years ago, I no longer have suitable space for one. And all the taps etc are designed for mains pressure. It may be best to just install electric showers and very small hot water heaters for sinks - we'll see when the time comes.

[@TimAndKatsGreenWalk]

@@SarahMould of course, there are always compromises to be made. Your plan seems very sensible. Incidentally, most modern unvented water cylinders run at mains pressure, gravity fed systems are very rare nowadays.

[@giachi75]

Hi Tim, Thank you so much for sharing your experiences and observations., I'm buying a house (not very big... 65 square meters) and I'm considering replacing the heating system made up of a gas boiler and radiators. I write from Italy, and here you could find a lot of information on A2W heat pumps, but practically nothing on A2A. the few videos I've seen often talk about A2A defects compared to A2W systems: they move air and dust, the temperature is not uniform, the environment heats up and cools down quickly, they are not silent... I still think that the correct way to use these systems is to let them run constantly, without waiting for the house to cool down. And looking at your videos (I also analyzed the consumption tables) I think A2A could be a correct choice. Before seeing your videos I had already focused on the Toshiba Haori systems: they have good performance, they work with external temperatures starting from -20°C, and above all the internal modules have a fantastic design compared to the competition. For my case I would use two RAS-2M14U2AVG-E units of 4kW each, for a total of 4 splits of 10000btu (one for the bedroom, one for the aisle and batroom, two for an open-space kitchen + living room of 35 square meters) To heat the water I would use a 110 liter monobloc heat pump water heater ( Ariston Nuos Evo A+ WH: it has great App for customizing time slots)

[@TimAndKatsGreenWalk]

No problem. I hope your install goes well!

[@StreetsToRemember]

Interesting video. This is a question I keep asking everyone since I moved to Ireland. But never got an answer for why there aren’t a lot more houses with Air to Air systems. Guess it’s just a historical preference. Two more things you missed out in pros is the automatic humidity control that puts an end to those black patches. Second one is the elimination of need for a separate ventilation system which would be required if there’s Air to Water System, I see a lot of new builds that have these heat recovering ventilation systems installed along with air to water systems.

[@TimAndKatsGreenWalk]

A2A doesn't give you ventilation or humidity control, the air is just circulated within the room, it doesn't get pulled in from outside. Humidity can be reduced indoors but only when using cooling mode, it doesn't reduce humidity in heating mode. We use dehumidifiers for that purpose instead. Mechanical ventilation with heat recovery would give you both those things.

[@colin6681]

Just stumbled upon your video this morning ( yes have subscribed now 😀)and find your explanation very thorough. I'm in the process of having my home heating sorted and probably will go with the A2A. During renovation I fitted new pipes to eventually install oil boiler outside, we all know now where that's going. So after a year ( or two ) looking at A2W, IR panels, pellet boilers etc etc it's A2A for me. One thing you didn't cover in this video ( and you did ask us to mention any uncovered topics ) is the ducted A2A supply. In my home I'll probably have the ducted supplying majority of the old section of house ( is a cottage so easy access through attic) and a high wall in the large extension which would be trickier to run duct too. My question is, are the ducted systems less efficient than the High Wall units , as in do they lose alot of energy before reaching the vent/room ? Thanks again and great videos

[@TimAndKatsGreenWalk]

At the time I made this video I didn't know much about ducted systems but now I wish I'd looked into them more. I think that would have been a better solution for upstairs in our house. I don't know the relative efficiencies but if the ducting is properly insulated I expect you won't lose much efficiency compared to the wall units. Neater too.

[@rajanpatel65]

Would be good if you could let us know how much electricity the A2A system uses in the differing climates in the future and their SCOP/COP compared to what they advertised too. Great informative video, again! 😊

[@rajanpatel65]

I'm torn between A2A and Infrared panels. Luckily I have an immersion heater for my hot water

[@TimAndKatsGreenWalk]

Yup, as mentioned that'll be covered in a future video.

[@geotock23]

Cost of use vid?

[@zweriuskriegsman]

I have an air to water system, that’s also being used for cooling. Partly by cooling the floors and partly by the use of separate cooling convectors.

[@TimAndKatsGreenWalk]

Nice. Sounds like a good system.

[@johnrush3596]

Cost wise , consider something like a mixergy combined with battery and solar . Divert what power you generate to battery and leave the mixergy to either heat the water on off peak in winter and anytime during the summer months. The solar diverter for mixergy does not seem to be worth it but the mixergy tank is very very impressive.

[@rolandashdown4903]

Great video - thanks for sharing. What would be of use is how you started the process of engaging the market and selecting your installer of choice. Any insights including lessons learned would be most welcome. Thanks.

[@TimAndKatsGreenWalk]

Yup, will try to cover that in a future video.

[@chrismgeary]

Our pros/cons list was more or less the same. Our hot water needs are limited to washing up after dinner, bathing is done with an electric shower, so the con of A2A not heating hot water didn't matter to us. We use about 3kWh of electricity to heat the tank via immersion each day and on Octopus Go that's very cheap - I can see us changing the tank at some point but its very low down on the list of things to do. We've not used any gas since July and that feels so very right. It's -8c this morning and the house is just as warm as usual (albeit the heat pumps are working for longer).

[@TimAndKatsGreenWalk]

Nice. Yeah, it's -8 here too and it's taken slightly longer for the house to get up to temperature this morning but it's just about there now. I can't wait to get our gas disconnected.

[@chrismgeary]

@@TimAndKatsGreenWalk Yes. I'm looking forward to getting our gas disconnected too. I've been holding off just in case but I think the last couple of days proves the A2A work brilliantly, even with our terrible, old, thermally bridging aluminium double glazing - that's the next thing on the list to update (after some room in roof insulation). It's so cool (no pun intended) that there are others who also took the A2A path - I also work from home so getting cooling as an additional benefit for a couple of grand less than the cost of an A2W ASHP system made it an easy decision.

[@TimAndKatsGreenWalk]

@@chrismgeary good stuff. Yeah, we were also seeing how it went this winter before deciding whether or not to fully ditch gas, and these last couple of weeks have certainly proved it's working just fine, so no worries there. I think a lot of people haven't even considered A2A as an option for heating, so hopefully these videos will give folks something to think about. Even if ultimately they decide A2W is better for them. It's all good as far as I'm concerned!

[@plasticcreations7836]

I'm starting to think about electric heating to replace our gas system. Your video is a great help. Some thoughts: 1) Would have been good to have seen some photos of your indoor and outdoor units 2) I think removing the radiators is both a Pro and a Con as you would need to pay someone to remove them and this could be quite expensive presumably as you would want to remove the pipes and get the walls replastered 3) Removing the old gas boiler could also be a Pro especially if its in a cupboard as you would also free up that space for storage. Could also be a Con because again it would cost you extra money 4) I presume that the company installing the A2A system does not remove the old gas boiler? 5) Are there any planning restrictions on where you can put the outside units?

[@TimAndKatsGreenWalk]

1) is answered in my other videos, go check those out 😉. Pipes can be left in the wall, I see no reason to go to those lengths. We're still using the gas boiler for water for the time being but will get rid of it in the Spring. Yes there are planning restrictions that are easily Googleable.

[@Damadchef]

I never really considered air to air heat pump until you said it cools as well 🤦🏻‍♂️... Yeah I've been watching your videos and thought you made a silly choice 😂.... 👏👏.. I guess im getting a air to air

[@TimAndKatsGreenWalk]

Well, there are pros and cons for any system. But the cooling really helped us out during the heat wave in September.

[@Damadchef]

@@TimAndKatsGreenWalk yes of course. I'm intending to buy a home next year and will hopefully be adding a similar set up... So I'm finding your journey very helpful... It really surprised me that I hadn't considered cooling the house😁

[@TimAndKatsGreenWalk]

@@Damadchef I'm glad you've found the channel helpful, that was my whole aim when I started it, really. Give folks something to think about. Best of luck with your own journey!

[@adamcole4808]

With A/C heat pump and solar + battery you can cool for free. If its a heat wave you will be getting great solar production so lots of excess electricity. My house in Spain has a 16kW hour battery and it easily gets us through the night without running out before the sun comes up. Even if we leave the A/C on in living room and cool two bedrooms to around 25oC.

[@TimAndKatsGreenWalk]

Yes, I'm looking forward to free AC next summer!

[@chrisjones6542]

Oh to live in Spain.. was it easy to get grid connected solar / batteries installed?

[@davidregan7213]

Very informative. On the cost front did you need to pay VAT?

[@TimAndKatsGreenWalk]

Nope, no VAT on the equipment or install, which was nice.

[@Electrat]

Thanks Tim, very informative. Can you tell me if the air circulation is good enough to heat rooms that don't have units in them, say a spare room that might not normally get used but now and then you may have guests?

[@TimAndKatsGreenWalk]

That depends a bit on where the units are in relation to the unheated rooms. For us, our hallway unit downstairs does a pretty decent job of heating the spare rooms upstairs when the doors are left open, as the warm air rises up to fill the upstairs pretty nicely. But it wouldn't heat the lounge on the same floor. We tend to open up the spare room a few days before guests arrive to let it equilibrate a bit, and that is usually enough to make it comfortable for sleeping in. We also provide a fan heater that they can then use for a bit of a boost if required but often they don't need it for more than 20 mins.

[@davidross1412]

Hi Tim, great video, very informative, I had one question about the A2A ducting, does this need to be insulated externally? Is the ducting you have installed insulated?

[@TimAndKatsGreenWalk]

The ducting itself isn't insulated but the actual copper pipes that carry the refrigerant gas are insulated inside the ducting. The ducting contains the flow and return refrigerant lines plus the power cable for the indoor units and the condensation drain to carry the condensation away from the indoor units when operating in cooling mode.

[@davidross1412]

@@TimAndKatsGreenWalk Hi Tim, many thanks, makes sense, no need for a trace heater near the copper pipes during very cold spells? I had a frozen Combi boiler waste pipe, so topical for me currently. I like the concept of the A2A.

[@TimAndKatsGreenWalk]

@@davidross1412 the pipes carry refrigerant gas rather than water so won't freeze in cold weather. We had no problems when it was sub zero for over a week in December, which was reassuring. Apparently it should all continue to work down to -15 deg C.

[@johncolclough625]

thanks again just binge watching these, what are you using for hot water is it an electric water cylinder

[@johncolclough625]

just watched video and got my answer heat pump hot water cylinder

[@TimAndKatsGreenWalk]

Yup, at present just the immersion heater in the existing cylinder. Hopefully the heat pump cylinder will be installed this Spring.

[@jason8966]

Nice comparison. Didn't you say in a previous video you'd also explain why you didn't end up going for infrared panels or am I making this up?

[@TimAndKatsGreenWalk]

No, I didn't mention IR panels in a video, but I may have replied to a comment that mentioned them? But basically, IR panels can only ever be 100% efficient where heat pumps can be 300+% efficient, so that's the answer.

[@zlamanit]

10:01 That's actually less disruptive in my case (a bunglaow - so just one floor with an attic/loft where ducting can be easily installed). And it can be combined with mechanical ventilation with heat recovery, which is often worth installing anyway, so ducting and vents are already there.

[@TimAndKatsGreenWalk]

Yes, I agree, mechanical ventilation with heat recovery would definitely be something I'd consider if I was building from scratch, or had a bungalow. Good point.

[@YamR1rider-wn9rf]

Good balanced video again. Personally, I think in years to come, A2W will be shown up as a great fallacy. I think here in the UK we are in a (Govt sponsored for A2W) interim period before new builds start transitioning to full ducted HVAC systems per the US. A heat pump is a heat pump - seems very wrong to me the Govt only subsidises A2W which IMHO at best is a hotchpotch effort to try and modernise the system yet sticking with radiators 'because that's what the British public wants and is used to'.

[@TimAndKatsGreenWalk]

I certainly agree that focusing the grants on only A2W is a mistake, it should be available for all heat pumps regardless of the heating source. It's one of those weird historical catch 22s that the UK is so wedded to radiators, but with so many existing houses with them A2W really is the only way to retrofit so many with heat pumps. As you say, hopefully new builds will start to see a move away from radiators but it'll take decades before alternatives even make a dent. In the mean time hopefully more people will start realising that there are actually alternatives worth considering.

[@karencampbell6884]

Hi TIm, for people like us it's so helpful that you share your experience and your abundant knowledge, thank you so much. We are having a whole house refurb and I have a couple of questions: 1) how does it feel to be in a room where the warm air is being blown down from above - do your feet and legs feel at all cold or does the air feel like it's an even temperature from top to toe (hope that makes sense)? 2) do you know of a suitable ventilation system that would work well with this product - we don't want trickle vents in our new windows and it may be that we only need an extraction system for the wet rooms (am I correct in thinking this system is bringing air in therefore we only need extraction)? Much appreciated, thank you.

[@TimAndKatsGreenWalk]

For the first question, we tend to have the fans on very low so you don't feel any sort of draft. The air mixes quickly and evenly so the room feels quite uniform. For the second question, this system doesn't bring in air from outside, it recirculates the air in the room. It's not a ventilation system, although you can get what are called HVAC systems which will do both heating and ventilation. Those tend to be more expensive, however.

[@karencampbell6884]

@@TimAndKatsGreenWalk thank you for all your help.

[@geoffallsopp3837]

I have one room with A2A and it is great but it does give dry air. And my wife likes radiators to air clothes! For water, I did wonder about thermal storage which is much smaller unit size.

[@TimAndKatsGreenWalk]

I've not found the air too dry as long as we direct it straight down so that it doesn't create a breeze. We use a dehumidifier to help dry clothes and it also provides a little extra warmth. I looked briefly into thermal stores for hot water and they look pretty neat.

[@BenIsInSweden]

One of the things on the costs is that the A2W install cost of ~£15K is including a guestimate for upgrading the heating system, when it comes to replacing it at EOL, the A2W will just be a fairly straight swap, for probably under £5k depending on the size of the unit. With multiple A2A units, you need to replace them all, e.g. (with current prices and taking advantage of BUS, you could end up paying £15K overall for A2W for a system that lasts 30-40 years (with 1 HP replacement in that time), vs yours, costing about £17K over the same period). Add on servicing costs for multiple A2A units over a single A2W over that time period as well, and overall cost does eventually go in favour of A2W. That said, I currently have a single A2A unit (Toshiba DSK 9.5) in our hallway, and am in a similar situation with a large house and currently only 2 occupants, so heating the whole house is likely going to cost more than heating certain areas, and likely next year will end up with the same multi-split system to cater for other rooms mainly for cooling.

[@TimAndKatsGreenWalk]

With any luck the cost of both system types will come down a lot over the next few years as they become more common. I hope so, anyway.

[@BenIsInSweden]

@@TimAndKatsGreenWalk One can hope. They are pretty common over here in Sweden (apparently 20% of all domestic heating), but in my town, it's closer to 80%, and they have been around for decades. Your prices seem fairly on par with what I would expect to pay over here. That said, a reduction in price is probably what's needed to break into the British market more.

[@philmorgan236]

What do the units and A2A pumps use electricity wise? I have a 10kw solar system with Tesla power wall, will it use all the power?

[@TimAndKatsGreenWalk]

As I said in this video, all that information will be forthcoming in a future video 😉

[@StewSims]

Can I ask - is there any internal stuff required other than the wall mounted units (which don't look too big)? Not sure we have the space for all the gubbins required for air to water. This seems like a good option combined with solar panels - The air cooling thing is a bit of a luxury but with our climate changing and the fact you could be using all that solar energy to help cool your home in the summer it makes a lot of sense.

[@TimAndKatsGreenWalk]

Take a look at the tour video I did prior to this one: kzbin.info/www/bejne/hnrKo4Fvqq-Zfrs Some installs will require more internal ducting than others but if you plan it right you can minimise it.

[@dj2006djdj]

Hi, we have air to air to replace oil boiler/radiators. We are finding the floor tends to have a cold air pool what did you find, ours is an 1980s bungalow so doesn't have floor slab insulation and laminate hard floors so that doesn't help? Yes same issues with bathroom heating and hot water. Trying an infra red panel in bathroom.

[@TimAndKatsGreenWalk]

We have carpet in most rooms and we haven't noticed cold air on the floor. The kitchen tiles are pretty cold, mind you, but I expect that'd be the same with radiators too. At least I seem to remember them being cold last winter as well.

[@TimAndKatsGreenWalk]

We also point the vents downwards to direct the warm air right at the floor where it then spreads out, so perhaps that helps?

[@justinc4261]

Our 1960s townhouse was built with a ducted hot air system (with a gas furnace/blower) - the ground floor has small ceiling mounted grilles, and upper floors have either floor mounted small grilles, or larger ones low down on the walls, basically one per room (apart from lounge). I love the extra wall space, and would hate to add radiators (which many neighbours have done). Logically, it feels like that should be ideal for converting to an A2A heat pump system! But I've totally failed to find any installer willing to quote for that - everyone seems totally fixated on wet systems :( Any recommendations?

[@TimAndKatsGreenWalk]

Interesting thought. That does sound like it should be doable. I guess anything slightly non-standard is going to be tougher to find an installer for. Good luck in your search!

[@coolkiwi79]

You’re probably better off looking at ‘Air-conditioning’ installers, they’re the really experienced people that would understand A2A systems, some mainly just do commercial stuff, but some mix it up - at least they all have the experienced compared to your plumbers and A2W Heat-pump installers.

[@Ambroseseeker1084]

Another pro is being able to migrate to A2A in steps. Half your system for 4K compared to 3k for new gas boiler is achievable for many more people who can’t afford the up front costs. The benefit of air cooling if we have another heat wave may make the expense easier to justify. I’m watching the pioneers before committing to change and don’t have a green agenda or particularly agree with climate change policies or time table and I think I’m in the majority. But I am very interested in your project and follow other pioneers like you and heatgeeks. Electric price is based on gas price and reforming that could make electric much cheaper and then the scop could make running heat pumps financially viable.

[@TimAndKatsGreenWalk]

Yes, good point about adding A2A incrementally, although with multi-split systems it can be better to just get it all done in one go (unless you need two multi-splits like us). I think the correlation between gas and electric prices will start to break down over the next few years (although it may take a decade), so yes, hopefully heat pumps will start to become more financially beneficial in terms of running costs.

[@jamesduffy8669]

Hi again Tim Can you tell me which Solar company did your install with Panels as well as the GIVENERY 9.5 batteries James D

[@TimAndKatsGreenWalk]

They're a small local company so don't have a wide reach. But their details are in the description of this video: kzbin.info/www/bejne/o2LQep-gjtl5mtU

[@PabloTBrave]

Is the outside unit the same for a2a and a2w can you have a combination of of both in one house.

[@TimAndKatsGreenWalk]

No, I don't *think* so. Usually an A2W system will be a monoblock heat pump where the refrigerant stays inside the outside unit and then heats water via a heat exchanger in that unit. Whereas A2A will be a split system where the refrigerant travels through pipes into the house where the inside units do the heat exchanging bit with the air in the house. I'm not sure it's possible to combine those two systems into a single heat pump but I might be wrong! At least I've not heard of it being done. There's nothing stopping you having two heat pumps outside your house, one for each, but not combined into one unit.

[@anonymousf7byyj]

You mentioned that there are air to air systems that do hot water too, can you share the names of those please? I’ve only found the Daikin Multi+.

[@TimAndKatsGreenWalk]

That's the only one I know of too.

[@LeiChat]

The manufacturers have managed to make the internal units quite sleek. Now they need to make the external condenser units slimmer (projection from the wall) and less industrial looking.

[@TimAndKatsGreenWalk]

Totally agree.

[@dbaby3288]

Can i use Air to Water to cool my baseboards? Currently i have oil furnace heating my baseboards? I really wan to get rid of oil because of the danger of spilling. I dont hate it but i would lose everything if it leaks. Can the same pump heat up the water, cycle it though all my baseboard and also cool the water during semi hot summer. I dont need a lot of cooling but a bit of cooling is sufficient. But I really need heating for winter as i live up north

[@TimAndKatsGreenWalk]

Some air to water systems can do cooling too. I'd suggest checking out the Heat Geek channel for more on air to water systems as it's not something I have any personal experience of. E.g. kzbin.info/www/bejne/mp-Xe5SVppqAb8k

[@dbaby3288]

@@TimAndKatsGreenWalk thanks. Checking

[@MCow123]

Don’t forget the need for planning permission in the UK (for A2A), as air source heat pumps that can cool as well as heat are not covered under permitted development.

[@TimAndKatsGreenWalk]

Actually you only need planning permission if the outside units don't comply with certain restrictions. E.g. less than 1m from a property boundary, or the total volume of the outside units exceeds 0.6 m3. There are a few others too (findable on-line). If it compies with all the restrictions then it does fall under permitted development.

[@TimAndKatsGreenWalk]

For example: lacltd.uk.com/do-air-conditioning-units-need-planning-permission

[@MCow123]

@@TimAndKatsGreenWalk Yes, clause G3 (a) is the one which specifies the heat pump can only operate in heating mode. www.legislation.gov.uk/uksi/2015/596/schedule/2/part/14/made I've fallen foul of this myself and I'm quite annoyed, as many of the installer websites actually say you don't need permission when in fact the above says you do. Most irritating. Also, G2(a) states that even if eligible under permitted development, this only applies to the first such unit. I therefore assume all 2nd and subsequent units would require permission regardless (even if they all only operate in heating mode). A bit of a minefield in classic government fashion.

[@TimAndKatsGreenWalk]

That's sneaky. You're right, most installers don't seem to know about this. In fact most don't even know about the 1m limit either! I'm hoping heat pump planning in general is going to get simplified in due course as at present it's really putting off a lot of people. It needs revising to help encourage better uptake.

[@MCow123]

@@TimAndKatsGreenWalk you're more optimistic than I am! On the one hand, they recognise the benefits of A2A hence why they're currently included in the 0% VAT deal, but on the other hand, they're not eligible for the current grants nor are they included in permitted development (if they also cool as well as heat). Are they a solution for gas boilers or not, make your mind up, Gov!

[@ragincrinz1457]

who fitted ours and where did you get it?

[@TimAndKatsGreenWalk]

A very small local company, I found on the internet.

[@ristekostadinov2820]

air to water heat pumps can cool, not every air to water heat pump can cool but there are ones who can do that

[@TimAndKatsGreenWalk]

True, although not as effectively given radiators tend to be low down so only cool a layer of air near the floor.

[@AdrianWalker247]

Can I suggest that you do an airtightness test on your house?

[@TimAndKatsGreenWalk]

As it happens I've been thinking of doing that very thing. The house is a new build so I'd hope it's pretty good, but it'd be nice to confirm.

[@engineerabetterlife8301]

@@TimAndKatsGreenWalk How did the installer seal around the pipework through the external walls? That would be a key point for your air tightness test.

[@TimAndKatsGreenWalk]

@@engineerabetterlife8301 expanding foam.

[@hvacdesignsolutions]

The big con with ATA systems, especially ductless units, is poor room air distribution, and uneven room temperatures in larger rooms.

[@TimAndKatsGreenWalk]

I guess you could always put more than one unit in a large room, if required.

[@PierreDybman]

In France you can get about 1000 Euros of subsidies for Air to Air Heat pumps, while you can get up to 9200 for Air to water, so that completely changes the calculations…

[@TimAndKatsGreenWalk]

Yup, sadly no subsidies for A2A but you do get £5k for A2W installs.

[@delrey-p]

I install these and I genuinely can't find any way at all that radiators can be more beneficial than A2A.

[@TimAndKatsGreenWalk]

Well, having now removed all the radiators I can certainly say that we don't miss them!

[@wobby1516]

Lounge set to 18-19c!! my wife would move out. 🥶 you must all sit around in fur 🧥 😅

[@TimAndKatsGreenWalk]

It ends up closer to 20 in the evenings when we're in there. 18 is usually for when we're not in that room much during the day.

[@USA-GreedyMenOfNoIntegrity]

You missed con. A2A mini split indoor heads have poor air filtration, difficult and messy to clean. Get yourself a 6mm or 1/4” thick foam pre-filter and spray with filter spray. Spray indoor coil with foaming coil cleaner every Spring to help keep coil clean and mold under control.

[@rogerphelps9939]

Air to air did not get any subsidy under the RHI.

[@TimAndKatsGreenWalk]

And neither does it qualify for the current BUS.

[@rodden1953]

Another Pro is it costs much less even without the Government grant , my system with the pump and 3 cassette were less than £5000 and only took a day .

[@TimAndKatsGreenWalk]

I don't think that's true in most cases, however. I'd say for a lot of heat pump installs you'd get an A2W system cheaper than an equivalent A2A once the grant is accounted for. If there was no grant A2A would be cheaper to install no question.

[@rodden1953]

@@TimAndKatsGreenWalk I'm not having a water tank , I'm going to get two under sink water heaters for the kitchen and bath room, i asked a plumber a few years ago to remove my bath but he never got back to me so thats my last big job but not important, I used the same guy as Nigel from The EV Puzzle to do my installation and it was less than £5000 , I've only had it for just over a week and I'm really pleased with A 2 A no mess and only took a day . . if i had gone with the grant god knows how much extra it would have been with all the extras they insist on having like the tank ,

[@TimAndKatsGreenWalk]

@@rodden1953 oh, I agree, the installation of A2A is so much simpler, quicker, and neater. That was certainly a big consideration for us. And after the last few days it makes me very glad we went for an option that gave us cooling for when we need it too.

[@jonnysegway7866]

Easy choice, Air to Air has once less conversion stage than Air to Water to Air

[@TimAndKatsGreenWalk]

Interesting point I hadn't thought of.

[@markosborne7311]

Did you have problems getting planning permission for your heat pumps?

[@TimAndKatsGreenWalk]

If the outdoor unit is more than a meter from a boundary you don't need permission for AC, but even if you do need permission generally it's not too hard to get nowadays as they're being actively encouraged.

[@mapryan]

@@TimAndKatsGreenWalk I don't think it's that simple. This is from the d-air website: However, you need to make sure that your external air conditioning unit follows these regulations: It isn’t bigger than 0.6m³ It’s over a metre away from any property boundaries It is more than a metre away from the edge of a flat roof It isn’t fitted on a pitched roof The sizing is key, especially if you're installing multiple units outside

[@TimAndKatsGreenWalk]

@@mapryan yes, true, I'd forgotten about those other requirements.

[@markosborne7311]

@@TimAndKatsGreenWalklooked this up. Under permitted development there are some silly rules. For example they allow one heat pump which would be larger and make more noise than two smaller ones, which requires full planning. It's a nonsense.

[@TimAndKatsGreenWalk]

@@markosborne7311 yup, there's not a lot of consistency.

[@Chris-hy6jy]

The defrost cycle is a negative in cold weather.

[@TimAndKatsGreenWalk]

Same for both. And it only takes 5-10 mins so not a big deal at all, really.

[@Chris-hy6jy]

@@TimAndKatsGreenWalk the cycle itself is the same in so far as the outside coil needing to be defrosted but I would say that the effect on the internal temp is probably greater with an A2A, especially a single split because all the defrost power is taken from the one indoor coil. You can literally feel the cold air falling from the indoor coil during a defrost cycle. This is probably less noticeable with A2W. Must admit, I don't have A2W so can't say for sure.

[@TimAndKatsGreenWalk]

@@Chris-hy6jy I've not noticed cold air coming from our indoor units during a defrost cycle. The fans all stop for a few minutes but that's about it. Perhaps different systems do it differently.

[@Chris-hy6jy]

@@TimAndKatsGreenWalk must admit, I've only noticed this on my floor mounted single split unit. Because a floor unit draws air in from below, the heat exchanger is exposed to the underside of the unit which probably makes this configuration worse. A high wall unit draws air in from above so the cold air probably doesn't "fall out" of the unit as easily. I have a high wall unit in the dining room so will try that today and see if it performs better during defrost.

[@TimAndKatsGreenWalk]

@@Chris-hy6jy hmm, that's interesting. Yeah, I expect there are differences in how the different units handle defrosting. Ours have certainly been doing it multiple times a day in the last week or so but generally it doesn't appear to have been a problem so far, which I'm grateful for.

[@Muppetkeeper]

As long as people stop using oil, gas or direct heat electricity, it’s all good with me.

[@Boz1211111]

Heatpumps dont work for everyone, be aware even in mild climate heatpump is very very inefficient when its cold

[@Muppetkeeper]

@@Boz1211111 Well mine has been running for 2.5 years, last week it was -2°C and foggy outside, and even with defrosts the heat pump was 300% efficient. Over those 2.5 years it’s average efficiency is 380%. That’s in a very wet part of the UK. What is your source of data please?

[@shawn7336]

No huge compressor?

[@TimAndKatsGreenWalk]

The heat pumps are similar sizes in both systems.

[@shawn7336]

@@TimAndKatsGreenWalk yeah I’ve just realised that what I thought was a giant compressor is actually a huge water container. I really like your system, but I need to find something to heat water too. But sadly I’ll need to rely on the grant, I think

[@TimAndKatsGreenWalk]

@@shawn7336 A2A tends to be a bit cheaper to install than A2W in the first place, so with the grant for A2W they can work out about the same. Water can be heated overnight on cheap rate using a timer on the immersion heater (if you have a cylinder already). Or there are heat pump hot water cylinders such as the Vaillant aroStor (quite pricy though).

[@shawn7336]

My home is a little smaller than yours, what did this cost please? If not a rude Q?

[@TimAndKatsGreenWalk]

@@shawn7336 sure, no problem. Take a look at this video, I go through the full cost near the beginning (you can use the chapter markers to jump to the relevant part) kzbin.info/www/bejne/hnrKo4Fvqq-Zfrs

[@Rick-ng3lr]

Another huge downside: Don’t forget the fluctuating temperatures and serious draft when the temperament outside get below 7c degrees… this occurs when the system is in defrost mode which can happen several times an hour for several minutes depending on your system…

[@TimAndKatsGreenWalk]

Nope, not on mine. There is no draft, the fans just turn off for about 5 mins, so doesn't really affect the internal temperature at all. And it only happens about every two to three hours (never multiple times an hour, for sure) and only when it gets below about 2 deg C, I've never seen it happen when it's as high as 7. All in all we hardly notice it happening, so not really much of a downside.

[@RobGregory]

One CON you missed is the defrost cycle

[@TimAndKatsGreenWalk]

Both systems have that so not really a pro or a con for either. My system takes about 5 mins to do a defrost and you barely notice it happening most of the time.

[@RobGregory]

​@@TimAndKatsGreenWalk I appreciate they both have to do it - after having mine (Air to Air) for a couple of months now I would say the 'defrost cycle' is the only real con for me (compared to running my Gas radiators). Definitely a small point compared to the running cost of GCH and having the cooling option though. Thanks for the reply.

[@RobGregory]

Dehumidifying is also a great Pro to have.

[@TimAndKatsGreenWalk]

@@RobGregory yeah, I didn't mention the defrost cycle in the video because I was comparing the two heat pump versions against each other rather than against gas, but it would be a minor downside if comparing either against gas, I agree. Thankfully ours doesn't seem to do it that often and only once it gets to lower than about 2 deg C, so not that frequently.

[@ecoterrorist1402]

still think you are mad getting rid of a 2yr old gas boiler, this also go's out to anyone with a boiler that's 20yrs old and less or condensing boiler, don't waste your MONEY, add one system in the lounge, but keep the boiler.

[@TimAndKatsGreenWalk]

You're entitled to your opinion but your argument is flawed. Continuing to burn fossil fuels simply because you have a new boiler doesn't make it the greener option. The lifetime emissions of a gas boiler vastly outweigh any embedded carbon in the manufacture of that boiler so replacing it immediately with a low carbon alternative is always going to be the greenest option. Take a look at "sustainable energy without the hot air" by David MacKay (free pdf is available to read on the web if you do a search) and find the chapter about energy saving light bulbs. It's a similar argument for replacing gas boilers.

[@CaptainProton1]

@@TimAndKatsGreenWalk An awful lot of people are going to die though from poverty chasing the new hysteria that is 'climate crisis' and that's coming from someone who is practically off grid ...electric car etc.

[@crit71]

I'm finding it bizarre with all this new found interest in split AC and people now calling it air to air 😂 I've been installing them for 35 years and they're just an AC split.....that's it. Very strange. Oh and Heat Geek know FA about AC. Just saying.

[@TimAndKatsGreenWalk]

Maybe not, but I don't watch HG for their AC/A2A knowledge 😉

[@ianfenwick2284]

There is no way a ASHP gives 3 to 4 coefficient. In the cold weather I would say you get 1 to 1

[@TimAndKatsGreenWalk]

Nope, definitely about 3. We went through a whole winter and it was great.

[@TimAndKatsGreenWalk]

Go watch this channel and learn more about them: youtube.com/@HeatGeek

[@paulgoffin8054]

A2A doesn't qualify for the grant because it's basically air conditioning - and air con makes it harder to meet our climate goals.

[@TimAndKatsGreenWalk]

Yes, I'm aware of that, although the amount of carbon saved in heating mode massively outweighs any extra used in the summer in cooling mode in the UK. Also, I'll be running my AC for free with zero carbon electricity from my solar panels!

[@paulgoffin8054]

@@TimAndKatsGreenWalk Overall though, the push for heat pumps is about "reducing the size of the problem". Adding air con doesn't do that - and yes, you're able to drive them at least partly from your solar panels but the converse is that your solar panels are then not displacing generated power from other uses. Personally, as I don't hold out a lot of hope that 3C can be avoided, let alone 1.5, I think we just have to deal with a reality of needing more air con.

[@TimAndKatsGreenWalk]

@@paulgoffin8054 using A2A as a heating solution is definitely a net reducer of emissions, even accounting for cooling use in the summer (which is a tiny fraction of the energy use compared to heating in the UK). Discounting A2A on that basis is a mistake imo.

[@paulgoffin8054]

@@TimAndKatsGreenWalk It's a tiny fraction because we have so little of it. The issue is that we have an energy use in the UK that is equivalent to a constant 180GW. To get to zero, all of that will ultimately need to be from zero carbon sources and 180GW average is a lot higher than the average electricity use which is close to 40GW. It's why we need to shift from gas heating, ICE vehicles, etc. Huge changes, huge costs and the most important thing is to reduce that 180GW as much as possible so as to minimise the massive investment in infrastructure changes needed. So anything that causes any kind of increase doesn't get taxpayer funding. Well, except for developing new gas fields or brown hydrogen plants, obviously 🙁

[@TimAndKatsGreenWalk]

@@paulgoffin8054 when I say tiny I mean relative to heating for me personally. For example we use our heating for 6 months of the year but would need cooling for maybe two weeks. The SCOP of our A2A is 4 compared to a typical SCOP of A2W of 3.5. That extra saving over the 6 month heating period will be more than sufficient to offset the two weeks of cooling use. I'm not disputing your point about making every effort to reduce energy use, I'm all for it of course, but saying that using A2A doesn't help reduce the energy demand of the UK is incorrect. The reduction in emissions for the purposes of heating is absolutely worth it.

[@TechAndMath]

I really don't think heat pump will be a good solution to replace gas. Better stick to gas and wait.

[@adamcole4808]

Did the Daily Mail tell you to say that? Sorry bit mean but do you have any technical basis to back up that claim? Mine works great even in a large and not particularly well insulated house. Yes its in Spain but is does go below freezing at night in Dec/Jan. I compared it to running a gas boiler the other day. Even not taking into account the savings from my solar it was about 2/3 the cost of gas in a 90% efficient gas boiler.

[@TimAndKatsGreenWalk]

Wait for what exactly?

[@TechAndMath]

@@TimAndKatsGreenWalk Gas is certainly best at the moment, unless there is a better alternative, I will stick to that. Do you get brainwashed by Guardian or some other place?

[@TimAndKatsGreenWalk]

@@TechAndMath Why are you watching videos about heat pumps if you don't believe they're useful to you?

[@TechAndMath]

@@TimAndKatsGreenWalk you have to ask google why they recommended me this channel?

[@Syess101]

Only 2 pros: Cooling and cheaper. rest of your pros are meh

[@TimAndKatsGreenWalk]

In your opinion.

[@Zebsy]

Does anyone have info how a2w works with Cooling, please? We have been quoted for a Daikin system: EBLA09DAV3

[@TimAndKatsGreenWalk]

There was a Heat Geek video about it last summer. Check out their channel.

[@zbiku82]

I'd add that refusing to the heat pump grant and installing a2a heat pump will allow you to keep your gas boiler and enjoy best of both worlds. Air to water systems have terrible performance if talking about heating up water or heating up rapidly! Additionally you will have two heating systems in case if one fail! Just my thought.

[@TimAndKatsGreenWalk]

As it happens we got our gas supply cut off this summer because the A2A system was so successful last winter (so no more gas standing charge). No gas used for central heating at all. A2W doesn't have to heat the house rapidly if run properly, as it'll be maintaining the temperature at a nice steady level (as we do with our A2A as well). We're planning on getting a Mixergy iHP (integrated heat pump) cylinder which apparently heats water very quickly and at a CoP of over 3, which is excellent.