Regarding cost effectiveness or "return on investment" for these various systems, I'm presenting these as options for folks looking to replace their hot water systems for whatever reason, e.g. replacing a broken or old system, or simply because they want to, I'm not considering the cost implications here, it's up to you to do your own calculations to determine if you feel it's worth it or not. I'll explain my own reasons for doing this in the next video, so look out for that one in the coming few weeks.

Only just came across this channel, loving it already. My biggest draw is that your presentation is not "Stop doing that! do this!" Instead, you're very clear about "Here are some more options for you to consider"

Tim, unless your mind is made up I have three words for you…SunAmp, SunAmp & SunAmp……we have been blown away. Reclaim a cupboard from all that cylinder & pipework, virtually no losses as almost no water is stored, mains pressure hot and cold to all taps, you already have the Eddi to control it plus it takes solar pv,. Ours has used cheap rate overnight power to charge for the first time this month since February!! We have the next to smallest unit and we have never run out of hot water….more than enough for a family of four or more. This is one impressive device. (BTW the Fischer units are made in Scotland by SunAmp and re badged…..they cost more!!

Many thanks, Tim. Jolly interesting. The heat pump cylinder is a revelation.

Great summary Tim and really useful to see all of this condensed and explained in one video. I installed an ASHP in May which complements my PV system. Working really well and, though expensive, delighted to be free of fossil fuel!

We switched to a heat pump water heater a few months ago and it works well in just heat-pump mode. We can use immersion elements if we somehow need them. If you have the right space and setup for it, it's great.

Great video Tim and all the options you mentioned are exactly the same process that I went through prior to my final choice about 3 months ago. The Mixergy by it self seemed a good option as it had some clever way of heating the water just enough for what you actual needed to use but the cost/efficiency ratio for me wasn’t enough to warrant the cost to buy it. They have indeed brought out a ASHP version that sits on the top of the cylinder but I dont think its available yet and from what i understand on pricing it wont be as competitive as other ASHP all in one cylinders. The Sunamp was one that I looked at about 2 years ago and they do look to be efficient for what they do but I felt that they had some major points that put me off, first is the actual weight of them, they are incredible heavy due to the internal heating mixture and just getting it into a house might be an issue especially if you plan on having it upstairs in the traditional location for hot water tanks. They do use much less room but probably the same footprint as a water tank just not as high. I didnt like the fact that I couldn’t obtain clear efficiency rates for what it would cost to charge the full unit and how much hot water it would provide. The other company Fisher - basically use a Sunamp which is rebadged from what I read back when i was looking at them. I decided on an ASHP all in one unit after much research and making sure i had a a hot water replacement for when I replaced my old oil boiler which did my heating and hot water. I went with the same setup for heating the house as you with the Toshiba Haori units and so far they are working out very well. Roll on the cold weather for the real test ! . The ASHP all in one unit I went for in the June of this year was chosen as it was more or less the only one I could easily obtain and at the price point that I was happy with. Installation was easy for my plumber, who had never installed an ASHP water tank previously but it was exactly the same type of water tank install as any other traditional water tank. He did worry about the ASHP part but he didnt have to do anything other than plump it into my existing hot water pipes and the electric. The Air flow is important so the location of these units needs to be able to get two 6 inch airflow pipes out to the outside of your house. The noise of them with the air flowing is minimal but I expect having it located in an upstairs hot water tank cupboard would not be the ideal place. I located my where my old oil based boiler was which was in the garage attached to my house and that gave me one of the air intake holes already due to the old flue for the oil boiler. So far I have seen at least a 50% decrease in my electrical use since installing it compared to heating my old hotwater tank on the electric element only. In summer I expect that rate to become very efficient but as we get colder days now i will reduce but if it saves even 1 kWh per day then its still a saving. I’m looking forward to your next video and to see what you finally went for. (I’ve not mentioned what I’ve got as the setup until after you have made your video) thanks for doing the videos :)

Another great and informative video, thank you. I am looking into an Air to Air source heat pump but I might cheat and try and get it all sorted in one go, like the new Daikin all in one solution. Though currently I have a combi boiler so need to find space in a modern house which isn’t easy. Looking forward to your next video going into more detail.

Thanks Tim and Kat. I love the fact that i can pretty much find all the information i need on any thing to do with going carbon free on channels like yours excellent excellent excellent. I am at the beginning of my journey into this. My plan is, solar on east-west roof, givenergy all in 1, zeb boiler and mixergy water cylinder. We're on octopus go as we ha an ev, so would use cheap rate over night to charhe zeb when not enough solar, hopefully winter only. Not sold on heat pumps as we have a 1950s bungalow with a double dormer that has micro bore up there. Ps just bought the thermal camera from the link in your video.👍

Thanks for putting this info together Tim! Very interested in the rest of your journey - we are about half way through a transition to A2A in our house (Panasonic Ducted Upstairs, probably sticking with Panasonic but wallmounted cassettes for downstairs). Still have a big Veissman 111 boiler for our hot water but been looking for a solution away from that :)

Old immersion tanks used to have 2 heater elements because of economy 7 switched electric. One element was controlled by the grid daily, and the second was used as a boost function if you needed more hot water during peak hours.

Love your approach to all this - clear and methodical without any preaching or nastiness so well done! My question would be are you facing the law of diminishing returns (in this case savings) in the quest to be totally self sufficient? If you have the funds to do so that's fine and very helpful for those of us who are still considering what to do, However, how many people can afford the sort of set up you have? Installation costs and ongoing maintenance, repairs etc to what are often relatively uncommon devices whose longevity is not really known and for which replacement parts may be very expensive and/or difficult to source readily and install. I'd be interested to know your total spend thus far v the savings you've made, what the break even point currently is and how that might change given the cost of your chosen new hot water solution. If any major parts of your setup failed beyond economic repair how would the replacement costs of that compare to say a new gas boiler or a problem with a the heart of a normal domestic electricy supply? Yes of course energy prices can always increase but the extent to which that's possible now must be limited to an extent by the very fact that we're much closer to the point at which people would ve freezing in their homes and business failures spiralling so the government would have to step in again to subsidise energy prices to avoid huge social unrest or unacceptable damage to the economy. I think what you're doing is very important and you know far better than I how complicated all these things are - how so many options are becoming available whose longevity and reliability haven't yet been tested over time and aren't yet common enough to benefit from cost savings due to scale of production. It's a problem in the car market with perfectly usable cars being rendered uneconomic to repair simply due to the cost of hugely expensive, scarce parts and limited suppliers. That's hardly green. I have a 12 year old Worcester Bosch Green Star condensing boiler which has been totally reliable (touch wood :) ), reduced our gas consumption quite a bit and cost me virtually nothing to maintain. I can heat the hot water by immersion if I so wish at cheap rates. A brand new one would cost c. £3k and will likely see me through another decade or so with little additional cost. My annual energy costs are around £2k with electricity being about 60-70% of that so I'm yet to decide what 'green measures' are going to be cost effective, all the time knowing that as time goes on newer, better and even more reliable and even greener alternatives will appear. For these reasons I'm reluctant to jump in and am finding your channel extremely helpful in forming my own opinions on how to proceed and would welcome your response to my questions. Cheers and good luck with what you're doing.

The HP cylinders are great. It's on my plan once a few other big jobs are out of the way. A point of note (I think): The higher the input temperature, the more efficient. I've seem some installs of this device in airing cupboards where the air input is ducted FROM the loft space and the air extract is vented outdoors (for summer time; roof spaces get relatively HOT). And in winter, the air extract is diverted back into the loft space to keep it a bit warmer. Point is, there are many ways to make use of the waste heat :). Have fun with this project.

Very informative video. We made the conscious choice of cutting down our fossil fuel use and installed PV 3 yrs ago and is a 2 electric car household. I have been waiting to change our 12 yr old veissman when it gives up the ghost and was disappointed when Octopus came and did the survey for a Daikin HP and was told we would need to put the pump in the garden as the regulations didn't allow installation in the side ( due to lack of space, space is premium in manchester suburbia even with large houses). They also wanted us to have absolutely humongous radiators and suggested running the pump at 45C. To top it all the guy who came whispered in my ear to stick with the boiler. My boiler died 2 weeks ago and I am changing to a system boiler (98% efficient Worcester Bosch ) with a tempest single coil HW cylinder hoping to heat the water at night with my cheap IO tariff and surplus PV elec during summer. While i want to reduce my energy use I am also a pragmatist and do not want to spend huge amounts for Sunamp and mixergy like devices. I feel exporting with the new Octopus tariffs does both for me. My only disappointment is sticking with natural gas for heating.

I looked into a sunamp before we had all of our system changed. It worked out VERY expensive with an A2W ASHP as it needs to be specced to be high temp. The PCM in the Sunamp needs 60C+ in order to charge. I went with a Mixergy. It can really only be half filled by electric directly. When using the heat pump it needs to be all done. The good thing is it uses an external plate heat exchanger so transfers more of the heat energy to the tank water. Tbh, in hindsight I would have gone for a Mitsubishi cylinder along with our Ecodan and used the Mitsubishi smart controls.

My Eddi uses around 7 to 9 kWh of electricity to heat the DHW cylinder. Havng an ASHP, I found it was 2 to 3 kWh to do the same . For now, the Eddi is triggering a home assistant automation to then turn on the ASHP to heat DHW, when there is sufficient spare solar. You have found some interesting options for those with the air heating system as you have.

I live in spain, i put one of those tube systems on my roof terrace 3 years ago. they work great for spain. i found i needed to put one of those electric filaments in the place it stores the water for about 6 weeks in the winter. Now bear in mind that the sun is out here for most of that time about 16c. So not sure how they would work for most of the time in Great Britain.

I've also been looking. I liked the Vaillant aroSTOR a lot - simple local controls which do most of what you need. Option for a voltage free contact to run either heatpump or "backup" resistive heater, so easy to add to home automation and keep everything local. Then mixergy put together their own heatpump integrated cylinder and started throwing mud at the serviceability and limited warranty of the "competition" (Heatpump dies -> new cylinder), but I don't want mixergy as they're asking for too much money for something overly dependent on their cloud service... which put me off both systems, and the gas combi I have now is working (if more carbon intensive than I'd like..) The Daiken looks interesting, previously looked at the Samsung EHS TDM+, but the indoor water unit is huge and won't fit where the old water cylinder was...

Couple of points Tim, firstly if you use the heat pump with a Mixergy cylinder, you have to heat the whole volume as it has a recirculating pump. And usually when you have solar thermal, it's an indirect system so you aren't circulating tap water directly through the panels. It is far more efficient to be circulating a fluid like glycol. A key advantage of a heat battery is that you don't need to run any sort of boost cycle to kill off bacteria as there is no stored hot water. The Daikin Multiplus is the A2A system I'm aware of that can heat water.

Thanks for the video, very informative! I’m in the process of looking at air-to-air systems, can you tell me which ones do water as well? I haven’t been able to find any so far.

Would love to hear more about a2a that can also do hot water.

Hi Tim, we are planning a rather similar air con and heating solution to you, and just to make you feel better about your choice I’ve been told (but I’m no expert) that all the air to air heat pumps available in the UK can’t do water as well, there are ones that do, available in the EU but they haven’t come to us here in the uk it seems.we are planning to upgrade my partners family bungalow, that was left to him (which we are retiring to sometime next year, I’m due to be made redundant no later than August 24 and we are selling up my flat and moving to north Norfolk), the bungalow was built in the 1970s and needs a lot of extra insulation and window upgrades, it has very old storage heaters one of which no longer works and still had it’s original old hot water cylinder that we plan to remove and replace, I hate radiators and my partner doesn’t want underfloor heating despite My best efforts to talk them round, so air to air is the compromise, seeing your system and the same make being used by several others has settle me on an air to air solution. And like you are planning to also a have a heat pump tank and are possibly looking at the Mixergy iHP. I will look forward to your next video on that! Throughly enjoy your videos. I’m planning a large solar panel and battery system too, my partner says I can use all my redundancy money on one and I’m currently planning on getting a system using emphases microinverters, solar panels and givenergy batteries, but (having listened to many Gary does solar vids and chatted to him about that I’m waiting until we are there as prices of solar installations are falling or will be by the time we move into our Norfolk bungalow. All our planned work is probably going to take long than I’d hope as I tend to overthink and so the planning stage will be extended as I rule out alternatives but so far all my above plans have remained my thoughts for several months now, so I think they are very likely to not change unless some new tech or newly improved solar panels etc. appear before our move. Thanks for hours of informative vids! Rob

Hi Tim thanks for another great vlog. I to didn’t know you could heat your hot water with an A2A system so I am looking at a Mixergy tank. I am told the heat pump on top of the tank is quiet?? So would be suitable for an airing cupboard?? The problem with all this change we are doing I have found little advice/ information on which direction to go. So have relied mainly on KZfaqrs like yourself to make my decisions and I thank you for that and sharing your journey. Best regards Simon

Nice insight to the options available . Seems like a very small return for an expensive investment, have you done any calculations on return of investment if using off peak tarriff in winter and free to heat with solar in summer

you could move the wiring on your existing cylinder as the unused heating element is higher up your cylinder so you would be heating less water

Tim..I have commented before and declare as a Mixergy fanboy😊. Firstly I would say 5kwh a day for a couple for hot water is a “generous” amount, unless you have daily baths. 2 x daily showers from my Mixergy is circa 2.6 kWh. (50 litres) Notwithstanding that, max efficiency from a HP cylinder will be a COP of 2.5. So in your case Mixergy vs Mixergy HP , the HP will save you 3kwh a day…30p in your case….but costs at least £1000 more and needs more servicing ! Also note, the Vaillant HPTank is an all in one unit….whereas the Mixergy HPTank is 2 piece, so in a worst case failure its not a complete loss [And yes the Fischer storage is just a re-badged Sunamp- at more money !] Keep on the journey👍

You should wire up the top and use that one instead and do something similar to the mixergy. There is a technology connections video explaining it. Also, I got a T Smart immersion heater that gives you some smarts for around 100 GBP.

Very useful summary. One or two responses have alluded to this but have you done the breakeven between the existing immersion using night-time tariff (at worst) vs the same on the heatpumps cylinder taking into account the capital cost of the latter. On a different topic would love to see in future your analysis of Octopus Go vs Intelligent Octopus. IO sounds better with longer off peak, lower ppkwh and double export (so more like flux...which incidentally my powerwall optimised very well...ie choosing when to export to grid from battery). Currently on Go....and whether the powerwall gets through to 00:30 is extremely sensitive to the solar generation.

We use Tesy Heat pump hot water cylinder

Intake air from the loft is the way to get best efficiency and Mixergy told me that you can fit the heat pump part of the system in a different location to the cylinder (obviously with a distance restriction) As my cylinder is on the middle floor of my 3 storey house I am still not sure how the pipes would need to run and the £3k plus instillation is also a problem.

Yes you could have gone to the air to water system to warm your house and hot water, but in the summer is where the individual heat pumps come into their own as chillers.

Are you considering a thermodynamic panel? Instead of the outside unit you have a panel on your roof or wall. I haven't seen much on KZfaq about them lately though.

Interesting.. Just for clarity and assuming a new water based ASHP where being fitted the ASHW-cylinder would not be needed? Would there be a differential between SCOP of an external heat pump plumbed to a specific compatible cylinder and that of a ASHW-cylinder? For some reason I had it in mind that the external ASHP only heated a hot water tank at a SCOP of 1 🤔

The second element on your water tank is usually wired in on an economy 7 system (cheap rate electricity overnight).

I am just about to start a major renovation on a 1950's bungalow. I am starting off with a wrap around extension and a dormer in the roof. The front of the house will have external insulation fitted and as it semi-detached I am also going to include some insulation on the adjoining walls. The roof is East West just like yours so I will have 6 in-roof panels on the front and 6 panels on the flat roof of the dormer at the back. I have designed in a plant room, as the garage is being demolished, and that will have a Mixergy tank, a tesla battery, connections to the underfloor heating from the ASHP and an MVHR controller along with one or more new consumer boards and a power supply for the car charger. My question is this, can the ASHP support the Mixergy tank as well as the under floor heating? or should I try and power the Mixergy tank from the solar. I think I understand most of how everything works individually but it is how I combine the various elements that I get a bit lost (also planning on having the Harvi & Eddi). Your thought would be very welcome p.s. I love the channel.

Does your current immersion have an adjustable thermostat? If not, you will be able to retrofit a thermostat with a relay for your immersion and you'll save many kWhs by heating the tank to 50 degrees instead of 60 degrees. Also a very cheap and simple upgrade compared to your other options.

Interesting options when considering A2A heating and how to heat DHW - we currently get approx 200-250 days of ‘free’ HW from PV diversion (hardly any in the winter due to the addition of a battery lat year which takes priority) BTW your explanation of how flat plate and evacuated tubes work wasn’t quite accurate - the water itself doesn’t circulate through them but through a heat exchanger mechanism depending on which type (usually filled with anti-freeze). Also evacuated tubes only have a header tank at the top - the tubes themselves are hollow much like a vacuum flask and have another tube within containing the heat transfer fluid which evaporates and carries the heat to the top to then be transferred into the header tank. They still work pretty well in winter and were all the rage along with thermal stores - they seem to have fallen out of favour over PV it seems but as a supplemental heat source could well fit the bill…

Using the immersion heater, the cylinder will fill up very quickly with limescale. Like a kettle. Having 60-65 deg water circulating in the cylinder heat exchange coil, minimises limescale deposition.

I'm currently weighing up options for replacing a gas combi boiler doing water and space heating (and maybe gain aircon in the process if I go down the A2A route). Thanks for this video, a helpful addition to my research.😀 Regarding the high-power (and relatively expensive) electric combi boilers, are they not sized as full replacements, to cover both hot water and radiators? I was under the impression that much smaller and cheaper units could be used just to heat the water (possibly separately for kitchen and bathroom), if space heating was being taken care of separately. Any thoughts on this?

For the ASHP cylinder would you not want to draw in air from inside? This would be more efficient as the air is warmer. The vent will want to go outside as the air will be cold, although in summer it would be good to be able to direct thisninside as well for cooling

I live in the US with an old gas powered hot water boiler and cast iron radiators that require very hot water to heat the house. Thinking about the possibility of either replacing the boiler with a Sunamp (if possible) or using Sunamp to heat a large tank of water and somehow use a heat exchanger in the tank to heat the water - instead of the boiler. How hot can the Sunamp heat the water? Any suggestions? I also am thinking of getting PV panels. Thanks, and great video!

I wasn't aware that some air to air systems can work for water too. Do you know of any systems in particular? If it can do that, that's kinda cool

We went down the route of the sunamp due to not really having a great space for a cylinder. Its been great. 0 maintainence is certainly a win. Ours is only charged by either PV or more usually cheap rate. But its heatloss is so low I don't think about it. Paring it with a heat pump would make it cheaper to run, the upfront cost of the HP would probably not be worth it unless you were doing A2W

What about the ZEB, it does central heating and water, very little change is needed if any, remove the boiler and plug in the ZEB. It would be great to get your thoughts on the ZEB.

Trying to decide between mixergy and sunamp at the moment… Mostly because of the boiler upgrade scheme requirement that the same heat pump has to do hot water as well…

Hello Tim, I am in the midst of taking quote to put mixenergy and then move onto putting heat pump, is this ok and more efficient than the cylinder that comes with heat pump?

Using a heat pump to charge a Phase Change store doesn't sound that efficient as the heat pump flow temp is above the melting point of the medium , which is above the required water temperature. Heating a water cylinder with a heat pump , the heat pump flow temperature is low while the water is cold & only rises as as the water temp rises so a better average COP is obtained ( in theory) .

Tim, your thoughts on this being a bit of a diminishing return? 5 units at 9p x 365 days approx. £165 p.a. for hot water reduce that to 2kw a day and your cost p.a. approx £65 A saving of £100 a year - less if you manage to end up on intelligent So isn't a further option Hot Water option simply to do nothing for the time being, perhaps even find a way to export just a little more and perhaps easily cover that £100 by other means?? Moving to Intelligent alone would cover that saving. I know, cars and chargers are the Intelligent issue. Just a thought?? All the very best Mike

I will try to get over my disappointment that you weren't doing cross stitch on a unicycle .....let it go me ! 🙈 I'm still not sure where A2A and grants are even though someone did say that combined with a HP water tank you could/might qualify. 🤔 So in the meantime I did sign up to trial with heata . (Hopefully I'll be selected) This is the data processing centre attached to the tank. Saw this fullly charged live. Might be worth your while 🤷‍♂️

Very interesting indeed , listening to you just tells me how little I know in regards to all of this modern stuff for want of a better word on the market , I like the idea of getting rid of my gas and getting a heat pump , but never seem to be able to find any information about the cost between a heat pump and a gas boiler , hear lots about how efficient the heat pumps are , tend to hear figures such as oh the heat pump is 160% or 400% more efficient well Great but how much is the cost from October to March month by month with cost , it’s like as though the true cost is being hidden, not the cost of the heat pump but the cost of running it , all people say oh it depends on what tariff you’re on yes that’s seem to be a cop out as I see it , there has to be some kind of chart or ball park figure yet nowhere can one find this information. Yes you will need a whiskey to get through this message at least you will be warm in the inside.

Oh exciting update, gets cup of chia and cinnamon roll to watch ……..

Hello Tim, I have an Ecocent version of your favoured ASHP on tank. It’s excellent! Very efficient. It draws from the landing, unlike your plan and vents out from the attic. It’s not that loud. We only hear it when we walk past the airing cupboard where it is. I recommend, but, like @buddywheels, if I had to replace it, Sunamp really interests me. Only issue with Ecocent is that it needs a pump to capture condensation. It recently went wrong and dropped water into the downstairs shower room. It happened during Storm Ciaron, which freaked me out; how could rain come in sideways and not from the roof?! Other issue is that it’s not great at handling a houseful. We are normally three but when daughters and spouses come down from London, it runs out and takes time to recover. Yes, there is a boost but fast it is not. Alex

Changing your current setup for hot water will never be cost effective. Better to spend money on more solar if possible. A quick change is to wire the top immersion heater instead of the lower one will mean you are heating less water.

Wont the servicing cost of a HP cylinder negate any savings you make ?

I'd stick with what you have, just make sure the controls are always pulling energy when its cheapest/free. It's a shame the multi-split A/C guys don't provide a solution for water heating, you could imagine a fairly simple heat exchanger on one of the loops, with the right set of valves in summer it could dump heat from space cooling into the cylinder. I'm sure its coming and it might make me look at a refrigerant based system over a water based one when it comes.

agree with being more efficient, but less is not always more…we went down the Fischer Aquafficient (210l) heat battery for simple reasons really: 1) size: no cylinder, moving parts whatsoever essentially space saving and a third of your cylinder size 2) zero noise & no annual servicing 3) compatible with solar & off peak charging….we literally never use the 210l available that is fully available and it recharges overnight (cca 5kW)….considering its off peak charging its a no-brainer to go down this route compared to 40-50db continuous noise and tripple the size solution just to get extra 3kW?with no real financial impact…

I am all in favour of A2A heating but why did you get rid of your gas boiler and then install such a massive tank? Doesn't make sense as heating water by electricity is far more expensive than having shower with a combi. What else do you wand hot water for anyway as I'm sure you have a dishwasher and washing machine both of which run on cold water. PS the top immersion is so you can heat a smaller amount of water which saves money

You have done so much up until now that you are pushing a case of diminishing returns. If net exporter is your goal, have you not looked into custom built Evacuated Tube Collectors to mount on the house front in that Apex area with the cylinder in the loft behind them for hot water. Like I said, custom....so it looks good and becomes an external house feature. Years ago people thought solar panels were strange and today they are everywhere.

Have you investigated ways to install a heat exchanger that removes the heat from the wastewater and heats your house so that heat is not wasted. 🤔

I wouldn't change what you have apart from wiring the top immersion you will never get your return on investment an immersion costs £20 changing your unvented cylinder for something else will cost thousands im a heating engineer of over 30 years and ive seen new hot water systems that are all singing and dancing and they don't last