Heat pump hot water cylinders - comparing specs

Let's talk about heat pump hot water cylinders. In this video I compare the specs for four different models that are/will be available in the UK in 2024.
Websites:
professional.vaillant.co.uk/f...
www.dimplex.co.uk/product/200...
www.daikin.co.uk/en_gb/produc...
mixergy.co.uk/news-and-insigh...
Data sheets:
professional.vaillant.co.uk/d...
product-portal.gdhv.com/sites...
product-portal.gdhv.com/sites...
www.daikin.co.uk/en_gb/produc...
mixergy.co.uk/wp-content/uplo...
Our home system summary:
6.8 kWp solar array split E/W
5 kW Gen 2 GivEnergy hybrid inverter
14.7 kWh GivEnergy batteries
A2A heat pump heating/cooling system
Myenergi eddi hot water diverter
Fiat 500e EV
00:00 Introduction
04:44 What are heat pump hot water cylinders?
05:56 Inlet and outlet venting options
11:02 The four cylinders
13:19 Comparing specs
32:54 Closing thoughts
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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[@sjhnmr]

Thanks for highlighting these systems - they are, of course, very niche in the UK, and few people know they exist, but they are almost de rigueur in countries where A2A is ubiquitous. A few observations gleaned from my own - very similar! - investigation. Space Requirements: The Mixergy's cylinder diameter is a bit misleading as to actual space requirements, because of the additional external siphon system. In fact, Mixergy specifies an installation footprint of 750x750mm for the iHP - probably fine in your garage, but sadly too big for the airing cupboard where my cylinder has to be. For those of us with indoor installation sites, the Dimplex Edel 170 has a potential advantage of using a concentric pipe arrangement, so that intake and exhaust air requires only a single pipe/hole-in-the-wall of 125mm diameter. The downside is the long reheat time, because the heat pump output power is limited by the (lower) air volume rates possible through the smaller pipes. Max. DHW Temperature: The EU specifications of the Daikin state a max. T of 62 degrees with the heat pump alone, 75 degrees with the immersion. Refrigerant: The R134a heat pumps really do have ca. 1kg of refrigerant - R290 not only has a lower GWP, but does its thing with much lower charges than HFCs (and the amount of R290 permitted in an internally-situated unit is limited by regulations!). This year's IPCC6 report has re-estimated R290's GWP as 0.07 at 20 years and 0.02 at 100 years. Does the refrigerant GWP matter? Yes! The standard assumption is that any refrigerant loop (even in perfect condition) loses 4-5% of its charge p.a., and that any R134a manufactured will eventually end up in the atmosphere over a 100-year timeframe. In other words, it is assumed that any HFC manufactured (for use in a heat pump) will end-up in the atmosphere, so the less HFC that is manufactured the better! R513a (GWP 573) is the modern HFC replacement for R134a (e.g. in the Tesy units), but ultimately, as the recent flurry of new monobloc A2W ASHPs demonstrates, R290 seems to be the way forward for domestic hot water heat pumps - it is somewhat surprising that Mixergy chose R134a for a new system (Mixergy probably wanted more power than the permitted charge of R290 could supply). Noise: The Sound Power Level of a unit is on the Energy Label; it relates to conditions set out in regulation EU813/2013, so should be directly comparable between units - but Energy Labels are not always easy to find on websites. Energy Label SWLs for the Dimplex Edel 170 and 200 are 48 and 53dBA respectively. I have a figure of 58dBA for the Mixergy (but it's obviously not from an Energy Label, so may not be directly comparable?). These numbers correlate well with output power - the Mixergy is loudest because it is the most powerful, and the Edel 170 quiet because its compressor is small. VAT-Free: Although these systems don't qualify for the Boiler Upgrade Scheme, an installation is eligible for the zero-VAT rate (on materials and labour) offered by the VENSAV scheme for energy saving measures. For simply buying a unit, I believe over-60s and those on certain Government benefits can qualify for VAT relief. Cheapest Option? For those who want to buy a unit (as opposed to an installation) I'd flag-up the Midea RSJ - globally the best-selling heat pump hot water system (very popular in Asia) - which is available in the UK from Tidyco for £717 (190L) or £1,155 (300L) ex VAT (two for the price of one Dimplex!). A drawback it shares with the Daikin (and other units potentially available in the UK, but not in your list) is the need for a sacrificial anode - Dimplex/Mixergy/Vaillant all have stainless steel cylinders that are corrosion-resistant (hence Mixergy's 25-year warranty). Intuis - the Dimplex/Vaillant Similarity: The Edel 200/270 and aroSTOR 200/270 are essentially the same unit with cosmetic differences. They are manufactured by Intuis, which is a French company that is part of the Glen-Dimplex group. The Intuis branding is replaced with the Dimplex one for the UK. I assume that the very slight differences in specifications between the Edel and aroSTOR may be a result of tweaks that Vaillant makes so that the unit runs to its preferences. The Edel 170 seems to be a Dimplex-only UK-specific unit - in Europe Intuis offers 150L and 100L variants. Sorry for the length of this comment, but I hope the information is useful to you and others.

[@TimAndKatsGreenWalk]

That's all really helpful, thanks for providing the extra detail!

[@VillageVidiot100]

You appear pretty knowledgeable on these. Like Tim and Kat I hope to move from gas to A2A heat pump - I have lots of solar and want the free summer cooling. As far as I understood it the boiler upgrade scheme does not rule out A2A specifically but simply says your space heating and water heating have to come from a heat pump - you can't have resistive only heating anywhere. If I could find a single contractor that would fit me an A2A HP and a HW tank HP in the same job do you think I'd be eligible for the BUS?

[@sjhnmr]

I'm afraid the BUS requires, amongst other criteria listed by Ofgem, that an eligible heat pump system: “provide both space and hot water heating and be capable of meeting the full space heating and hot water heating demands of the property” “be hydronic [transfers heat to a liquid for the purposes of space-heating]... Air-to-air systems are not eligible” "be certified by the Microgeneration Certification Scheme (MCS)” Your preferred arrangement can't meet these criteria. If you want blown-air heating/cooling, instead of using conventional radiators, you could look into using hydronic fan-coil units with an ASHP - which would qualify for the BUS.@@VillageVidiot100

[@VillageVidiot100]

@@sjhnmr Thanks for that, really appreciate you coming back to me. Any suggestions of preferred manufacturers who make a good hydronic fan coil that is similar to an a2a wall unit?

[@sjhnmr]

I don't have any personal experience of hydronic fan coil units, but some people on the buildhub forum have shared their experience with them. Smithsep has a wide range of styles, but the high-wall units are much larger than an A2A HW fan coil. The Cool Energy Reverso is a designer unit that would better suit a domestic setting. The big brand heat pump companies, e.g. Mitsubishi, Daikin, Panasonic, have models, but the domestic variants are floor-consoles and expensive - more than the cost of an entire A2A single-split from the same manufacturer!@@VillageVidiot100

[@Torchman-]

13:00 Thank you for taking the time to compare this all. As you mentioned, being a data geek, it drives me livid when manufacturer's put their own random spin on specification sheets. Thank you for taking time out of your life to make it easier for consumers!

[@TimAndKatsGreenWalk]

You're welcome. I hope I got all the numbers right! It's made it easier for me too so I'm glad I did it.

[@colingoode3702]

Been waiting for this one. Paused while I get a cuppa Tea & settle in for the watch. BTW I'm also looking at Sunamp thermal storage batteries as an alternative to integrated HP HW cylinders. Not as efficient but easier to find space for & more flexible location options. I hope you are both on the mend & have a great 2024.

[@TimAndKatsGreenWalk]

Yeah, there are definitely space benefits to the Sunamp system. We're lucky we have a couple of options for siting a cylinder.

[@lewispearson]

Congrats on hitting 1 million views across all of your videos :) and thanks for the detailed breakdown. 2023 was the year we finally got a battery, 2024 is the year we start to seriously look at moving away from gas central heating (combi boiler), so I'm intrigued to follow your journey

[@TimAndKatsGreenWalk]

Thank you! It's great to hear you're making good progress in your own journey too.

[@johnhunter4181]

For this winter I've moved the air intake of our MVHR from the outside to the attic. Even though we are now drawing a lot of air in through the soffits, the attic is always at least 4°C warmer and when the Sun comes out (as in the past few days) it's 8°C warmer. At the end of the day, if our house is losing heat to the attic then at leat we are recovering some of it - as would a hot water tank HP. The heat in your attic will eventually go to the outside - grab it while you can? Not the same scenario if you install in the garage of course because you probably do want some warmth in there.

[@TimAndKatsGreenWalk]

If I install this in the garage I'm definitely not using the garage air for the intake, it'll absolutely need both vents going to the outside.

[@stephenwyatt-yg9xb]

Thank you for distilling all of that - saved me days!

[@TimAndKatsGreenWalk]

No problem, I'm glad it was helpful.

[@bobbazley5376]

Oh exciting just what ive been waiting for :) hope your both feeling better and Happy Hogmanay :)

[@TimAndKatsGreenWalk]

I mean, you're kinda already sorted, no? I think we're both over the worst of it now, thanks. Happy Hogmanay to you too!

[@bobbazley5376]

Yes I’m happy with my choice and my garage is not within the envelope of the house as it is attached and accessible via the main house but is not within the houses cavity wall build but a single build which i plan on creating a insulated wall within the space. What I did notice that my cold water pipe that was extended to the garage for my heatpump actual had froze one day so I corrected that by applying more insulation around the the part that was frozen and thats corrected the issue. The noise level is not really bad other than the sound of air that is going through the top but that will be very much reduced if you vent both pipes outside. I did look at the mixergy prior to my choice of unit but they didn’t have the airsource option available and I needed a solution for hot water quickly after going over to a complete air2air heating solution. I think all the choices that you have discussed will give you more or less the same performance with slightly different effiencies in different scenarios. Keen to see how the Mixergy performs when you get it.

[@TimAndKatsGreenWalk]

@@bobbazley5376 yup, I'm looking forward to getting this sorted soon. Not exactly sure when that'll be but within the next few months, for sure. I'm glad you're happy with your choices so far.

[@swisby3820]

Heat pumps using a refrigerant with >150 GWP is about to the target for the EU under the new 2024 F-Gas regs (coming into force within the next 2mths) so manufacturers who look to market to the EU are very likely to switch to R290, even if it is a combustible A3 classification gas.

[@TimAndKatsGreenWalk]

Yup, in fact I spoke to Mixergy and they are switching to R290 before launching the iHP.

[@JJ-zg1hh]

It could be worth an inlet and outlet pipe arrangement which includes diverter valves for summer and winter set ups. On a hot summers day you may want to suck the warm air from the house and discharge the cold air back into the house (i.e. free air con), and in winter divert both pipes to the outside to avoid robbing heat from the house.

[@TimAndKatsGreenWalk]

Yup, it's just a matter of practically at the end of the day and whether it's possible to have all those vents going to different places. If it's doable then great, but it's probably not worth the extra complication or cost in most cases.

[@JJ-zg1hh]

@@TimAndKatsGreenWalk agreed.

[@Umski]

Combined with MVHR this could be an interesting experiment 🤔

[@sjhnmr]

Take a look at the Joule Modul-Air, the Genvex Combi and Nilan Compact that do exactly this - and provide hot water for space heating too.@@Umski

[@theoddjobcentre6686]

​@@TimAndKatsGreenWalkwe want rid of our hot water cylinder as don't use it and it takes up alot of space

[@sjdiy8230]

In the summer taking air from your hot loft would be a good idea and then as the exhaust air will be dehumidified and cool, in the summer it would would be beneficial to pipe that into your home as this should help your A2A cooling efficiency. In an ideal world if you are able to setup the ducting with bypass dampers on the intake supply to extract air from loft or outside as needed. Do the same on the exhaust, reuse the cool air internally on hot days and redirect it out on cool days. That would probably optimise the overall efficiency. For those with solar panels on the roof, especially those with in roof panels, it would be interesting to know if cooling the loft space in this method would improve the solar panel performance. I have seen some installs which extract air from bathrooms into the the intake of the heat pump cylinder, which is nice way to close the loop where you don’t have MVHR system. In that scenario you would want to exhaust directly outside to avoid odour issues. Still looking at the Daikin multi plus as this does, the heating, cooling (max 3 indoor units) and hot water albeit max 120L with one external unit.

[@TimAndKatsGreenWalk]

Indeed, you could get very creative with the ducting but it'll probably end up being a practical consideration, since the duct runs would end up getting very long in some cases, and probably need to go through ceiling voids and such. Now if I was building a house from scratch that sort of arrangement would definitely be worth considering.

[@meehall3960]

Thanks for the video Tim. We don’t have a heat pump yet. The Daikin Multi+ is on our shortlist as it heats water and allows 3 internal air to air units. 👍

[@TimAndKatsGreenWalk]

Nice. Yeah, I wish I'd known about that one when I first looked into this stuff. I suspect it ultimately wouldn't have been sufficient for us but even so, it might have been worth a look.

[@theholyfamilyallsaintscath2899]

we fitted a brand called Tesy, its a 250 litre cylinder with a heat pump on top. We are happy with it .

[@TimAndKatsGreenWalk]

Good to know. I expect we'll start to see more and more models become available in the next few years in the UK.

[@chriss4949]

Great vid Tim. Love my Mixergy ( standard non vented) . You will enjoy the data you can get from them

[@TimAndKatsGreenWalk]

That is something I'm looking forward to a great deal 😉

[@johnrush3596]

Good video. We have a standard mixergy 210lt tank with a ecodan heat pump. The comment on the mixergy is we always have hot water even with a familyof 5, it manages the levels really well. Ours stays around 50% at the moment, but that will change once some of the house renovations are completed when other demands are put in place. The time for new hot water to become available is very very quick should someone attempt to drain the tank completely, and I say attempt as the unit starts to heat water when the level gets below a set level. Yes, mixergy tanks are more expensive than others, but they seem to work.

[@TimAndKatsGreenWalk]

That's good to know. Hopefully we'll get this sorted in the next few months and I can start to report back on the performance.

[@mrjamerst]

I'm in a very similar situation to you - I'm renovating a property and will be installing air-to-air heating. Previously hot water was just provided by a barely insulated vented immersion cylinder, so that definitely needed an upgrade. Just a couple of things to add from my own research in case they are useful for anyone else: - Thermal loss for Daikin cylinders: 1.512 and 1.704kWh/24h for the 200 and 260L models respectively (just found in datasheet, listed in watts under "Standing heat loss") - Daikin max temp: 55C Personally I will (hopefully) be going with the Daikin cylinder, I've received a quote and put an order in, but I'm just waiting for stock since it's new to the market. The Mixergy cylinder is appealing (hopefully more maintainable, probably better controls, wider range of sizes - 200L is too big for me really). The significant price premium puts me off though (around £1000 ex vat based on the prices I have got). Just didn't seem to be worth it given that my energy usage for hot water will be fairly small in comparison to space heating. I'm not on a smart tariff either, so the reduced reheat time doesn't really matter that much - it can just be left to run whenever necessary to keep warm. The Daikin Multi+ system would be perfect if only it had capacity for an extra indoor unit - I need 4 units but it only supports 3 annoyingly!

[@TimAndKatsGreenWalk]

Ah, great, good find. Not sure why I didn't find that Daikin datasheet. Best of luck with the renovation!

[@davidcoates6768]

Great analysis. The loft space should be well ventilated to keep it dry, so the air will change quite often, so might as well grab some heat which has already been lost, there may also be a concentration of cold air at ground level from the existing air to air units. But at the same time I wouldn't want an extra pipe going up through a room, maybe through an airing cupboard though. Personally I would oversize the cylinder if you have the option to only heat part, the givenergy car charger should get added to intelligent at some point, giving you 6hrs+ off peak.

[@TimAndKatsGreenWalk]

There are still a few details regarding the installation that I need to nail down before any final decisions are made, but I'll be sure to cover the whole process in due course. It's totally possible all of my assumptions will be turned on their head, so I'm absolutely open to things changing if required! Watch this space.

[@NickAskew]

Thanks for this. I'm actually most likely to choose a air to water system and had been thinking of the Mixergy. I must admit that I was a bit worried as I misread that heat loss figure and thought it said around 1.01-1.75 kWh per hour not per 24 hours and was really worried that I'd be losing 24-42 kWh per day and figured that I'd be using huge amounts of electricity just keeping the water hot. When I read it again and realised it was that much in 24 hours I was a little less worried. 🙂

[@TimAndKatsGreenWalk]

Haha! Yeah, that would be a lot of wasted energy. Thankfully modern cylinders are pretty well insulated. You'll probably find that an air to water heating system will come with its own hot water cylinder so you might not need to get a separate one. Unless you're planning on getting a regular Mixergy cylinder to start with (without the heat pump on top) and then getting an A2W system later down the line when you'll be able to make use of that Mixergy cylinder.

[@soundslight7754]

I'm very grateful for this video and the information provided as it triggered the thought process. I find myself torn between two alternative thoughts: 1. As you produce own electricity and can heat water at at cheap off-peak rate, why not just continue with immersion heaters, possibly instant heaters at the point of use? Payback period of HPHW seems to be well above 10 years (in your case) plus risk of failure then having to replace at big expense plus the risk of going for a time (days/weeks) without hot water. 2. Adding to battery storage is more cost effective than HPHW

[@TimAndKatsGreenWalk]

Cost effectiveness is not my main concern here, as I mentioned in the video. However, you're right that the payback isn't really worth it when considering just the financial perspective. Adding to battery storage might also not be worthwhile beyond a certain point, but that's a calculation I'll be showing in the Spring once I have all my heating data available.

[@davidstewart1153]

The intake and exhaust routing can drive you crazy as someone will argue against all possible configurations. Probably just go with what fits. My US model seems to make most of its noise at the intake, and I've seen suggestions to improve the intake air filtering to keep the coils clean. So I plan to build an intake box and large filter to maybe quiet it down and make it last longer. The noise isn't very loud but is distinctive and not pleasant - sort of a higher frequency rasp to it. In the summer I plan to draw intake air from outside.

[@TimAndKatsGreenWalk]

Indeed, it'll come down to what's practical in the end.

[@lisa3jemima]

If you have 10Kw of battery and 5Kw inverter in the loft creating heat, would that make it a better option for the inlet coming from the loft? Possible switchable vent so you can switch to drawing for outside during the winter to not over-cool the loft?

[@TimAndKatsGreenWalk]

Possibly. It comes down to practicality more than anything, as often it's too complicated to install something along those lines.

[@roryparker9885]

I installed the arostor 200L in June and the inlet went into the eaves of the chalet bungalow we just built. It worked perfect in the summer. We situated it into a cupboard with sound insulation and the noise has been fine. The chalet bungalow is a self build and we opted just for electric. We put in infrared heat sheets, solar panels and then the arostor. I have found that since October we are using a lot of energy and wondering whether the heat pump drawing in air from the loft could be a factor. It seems like the cold air is making it work a little bit too much. I wonder whether it would be beneficial to draw air from outside in the winter or warm air from the inside of the house? Im undecided.

[@TimAndKatsGreenWalk]

The problem with drawing warm air from the house is that you then have to heat that back up again so you'll then use a lot more extra heating. I don't think you'll improve your situation by moving the inlet, it's just one of those things that heat pumps will have to work harder when it's cold. It'll still be significantly more efficient than any other form of heating.

[@HowardBurgess]

For Vaillant A2W heat pumps there are strict clearances from opening windows etc. This is in case the flammable R290/propane refrigerant escapes. Interesting that their R290 integrated heat pump cylinders can be placed indoors without any precautions. The outdoor units do contain more refrigerant (e.g. 0.6 kg for the 3.5 kW version vs 0.15 kg for the cylinder featured here). However, it’s a shame that they put such strict restrictions on their outdoor units, which means they often can’t be sited where you want them.

[@TimAndKatsGreenWalk]

Yeah, that is weird. Siting heat pumps outside is one of the most annoying aspects, so making it more difficult doesn't help!

[@geoffreycoan]

Interesting. I was astonished at how long these heat pump hot water cylinders take to heat a tank from cold, and went to look at our own ASHP timing and data which presumably is slightly less efficient as the hot water has to run all the way from the ASHP outside through the house to the cylinder in the middle of the house. We only heat our tank once a day, overnight on agile in the winter and midday in summer in free solar. A cylinder full lasts a whole day for us. By comparison, ours takes about 30-45 minutes and usually 3-5kWh although has been as low as 1.5 and as high as 6.7kWh. So actually, when considering that the cylinder heat pump is only 800W, it’s not dissimilar although with a much longer heating time it’ll be less easy to run it in the overnight cheap slot (depending on the tariff you’re on. Flux quite short for example). Personally I’m not convinced by Mixergy, they seem an over engineered and over priced solution to a problem that I don’t think many people need solving. But that’s my personal opinion. The separate heat pump from the tank is a good thing though.

[@TimAndKatsGreenWalk]

Generally speaking you won't be fully reheating a totally cold cylinder, so I expect the reheat times in normal operation won't be anything like as long. Hopefully!

[@geoffreycoan]

@@TimAndKatsGreenWalk one disadvantage of our ASHP setup is that it can only heat the radiators or the hot water at one time, not both (I thought that’s what 3 way valves do, but who knows). So to keep the house nice and warm (and only heat the tank on cheap electricity) it’s only once a day heating of the hot water cylinder. It does sometimes get down to 15-20 degrees in our tank. You won’t have this restriction with a separate hot water heat pump so maybe you can keep yours topped up all day.

[@richarddixon6354]

Another very informative video, thank you, though I am a bit late to this. Interestingly I read in another comment you had 2 Heat Pumps installed, did you require planning permission? I have seen this on another KZbin account but I think they are in Wales. Finally I saw today in an Everything Electric video that Mixergy are launching a new product this year called CubeX which is smaller.

[@TimAndKatsGreenWalk]

Yup, planning permission was required because the units were closer than 1m from the boundary as well as there being two of them. I spotted that new Mixergy CubeX while browsing their website the other day. It looks intriguing and I shall be finding out more about it.

[@NickAskew]

Regarding legionella and the mixergy system. The bacteria could easily survive in the lower cooler part of the tank so I guess the routine cycle is more important in that case. My wife is a microbiologist and she insists we take this seriously.

[@TimAndKatsGreenWalk]

The Mixergy heats the whole cylinder because it uses a plate heat exchanger in the heat pump and sends the hot water right to the bottom (when in eco mode), rather than using a coil which would leave a layer of cold water below. Pretty handy.

[@NickAskew]

@@TimAndKatsGreenWalk I think you mean that it can heat the whole tank not that it does because famously a feature of the mixergy is the separate layers that it maintains. Now I agree with you that a normal tank would indeed have a problem too if they cannot heat up the layer at the bottom. But unless the whole tank is heated, the bacteria will form a film on the parts of the tank that remain below the critical temperature and this video did mention that normal tanks tend to heat up the entire tank. But if the mixergy's cleaning cycle also heats up the entire tank once in a while, that's fine.

[@TimAndKatsGreenWalk]

@@NickAskew the iHP works a bit differently to the regular one. In eco mode it heats the whole tank and that's the mode you'd normally use as it gets the best efficiency. In boost mode it heats the top, like the normal version. The normal version can and does heat the whole tank in a cleansing cycle, but you're right that in normal operation it'll only heat what's needed at the top. The iHP will heat the whole tank most days, however.

[@tom95521]

Extracting heat from the attic to input into your hot water heater makes sense if you have a well insulated ceiling. In a ventilated attic the air temp in winter should be close to outdoor temp. During the summer months the extra heat will make the hot water heater more efficient. Instead of a vertical pipe into the attic I would use an elbow or tee stove pipe at least a foot above the insulation with wire mesh cover to keep out dust and rodents.

[@TimAndKatsGreenWalk]

It depends where it's most convenient to put it really. If the cylinder is on the first floor and isn't next to an external wall then venting to the loft makes sense, if it's in the garage next to an external wall then venting outside is more convenient. The longer the vents and the more bends you add the lower the efficiency of the heat pump, interestingly, so keeping the pipes as short as possible and with as few bends as possible is preferred.

[@UpsideDownFork]

Great content. I think your conclusion that drawing warmer air from the loft will encourage colder air to make its way into the loft is correct, but the amount of heat lost from the thermal envelope of the home must be insignificant. I have no calculations to back up my assumption, I'd just imagine that the cylinder won't draw more air than is already being forced through your roof space through the existing soffit vents anyway? On the DHW temperature issue, since having our A2W heat pump installed we heat the cylinder to 48 degrees. For us it makes sense as we are all young, fit and healthy as well as emptying the cylinder almost completely every day so the risk is almost zero. Surprised that R290 is being used indoors when some regulatory bodies kick up such a stink about putting R290 heat pumps out in the garden! I think it's a storm in a teacup. Its such a tiny amount of refrigerant we're talking about. Charts like you've produced are helpful and even A2A and A2W heat pumps could really do with more standardisation!

[@TimAndKatsGreenWalk]

I suspect you're right about the heat being taken from the loft having an insignificant effect on the house overall. It's possible a hotter loft in the summer might provide some benefits to the heat pump, however, so I'm keeping an open mind to the option. I agree regarding the R290, the charges are so low that the risk seems very small, but there you go. On the Mixergy website they state that this is one reason they're using R134a instead. I'm also constantly amazed by how many people are so paranoid about legionella, there seems to be some ancient dogma that has long since been superseded by more up to date advice but still it persists. I did enjoy the excellent video Heat Geek did on the subject last year.

[@UpsideDownFork]

​@@TimAndKatsGreenWalkI've been recording my figures for my A2W heat pump. The part that may interest you is that although the ambient external air temperature has a great effect on the CoP for space heating it appears to have a lesser effect of the CoP on the DHW cycle. I assume this is due to the higher flow temperature needed. Although I do have a range from 2.6 up to 4 for the DHW on the same days, the heating was 2.8 and 5 respectively. I recognise that my hot water cycle typically takes 60-90 minutes for 200 litres so my pump will be consuming more energy over a smaller period of time, hopefully some of this data is relevant to the integrated cylinders that you're looking at. I haven't drawn any major conclusions yet and I'm keen to see how it tracks throughout the rest of the year but maybe there's some data that interests you. kzbin.info/www/bejne/n6q0nauqo96Sarc

[@TimAndKatsGreenWalk]

Just watched your video. Very interesting! One thing I regret about the A2A system we have is that I don't have any way of measuring the CoP, like you can with A2W. I suspect that a good A2W system is more efficient overall than A2A as you can fine tune it to the house. A2A is more of a blunt instrument so needs a bit more manual fiddling day to day and is unlikely to be as well balanced as A2W. Still, pros and cons, I suppose. I'm glad your system is working well for you though, and congratulations on getting off gas entirely! Oh, and I totally agree about boiler efficiencies, there is no way anyone is getting more than 90% in the real world, I think your assumption of 80% is much more reasonable.

[@UpsideDownFork]

@@TimAndKatsGreenWalk thanks for watching. Your channel inspired me to capture and organise my data in a less casual way and I hope that me sharing mine will benefit others in the same way that your data sharing has benefitted me. If we spent extended periods of time in one or two rooms then I could see a very strong case for A2A being more economical to run. As it is, life with 3 kids means the whole house needs to be heated pretty consistently and A2W appears to be lending itself to that. There appears to be a bit of tribalism between the two in the heat pump groups which seems silly as both are great implementations of the same fundamental technology. 👍

[@TimAndKatsGreenWalk]

@@UpsideDownFork urgh, I hate any form of tribalism. There's really no reason to be so polarized. No system is universally better in all situations so it's worth keeping an open mind. Anyway, I'm glad my channel has helped you and I hope your channel helps others in turn!

[@Eggnog3000]

Have you purchased the mixergy cylinder yet? Think I'm now convinced it's the one to go for...Going to try and order this week!

[@TimAndKatsGreenWalk]

Well, you might find that a bit tricky because it's not available quite yet. I've got more news on that coming soon though, so keep your eye out for that.

[@Eggnog3000]

@@TimAndKatsGreenWalk OK... I'll call mixergy tomorrow and see what the deal is... Oil boiler is on it's last legs...!

[@StefNoci]

There's very little info on KZbin about sunamp thermal batteries, I know you talked briefly about it, I was just wondering why you dismissed it given your solar set up, air to air & space saving benefits? Just curious....

[@TimAndKatsGreenWalk]

Simple, it comes down to efficiency. Heat pump cylinders are 300+% efficient, Sunamp (or similar) are only 100% efficient. I mentioned this in the video where I discussed Sunamp along with the other hot water options. We don't have a need for the space saving that Sunamp offers, so a heat pump cylinder gives us that efficiency benefit.

[@edc1569]

In a garage you might want the ventilation of having it pull air from the garage space, lots of garages have damp issues

[@TimAndKatsGreenWalk]

We don't seem to have damp issues in our garage so hopefully that's not a problem, but venting is definitely something I'll be discussing with installers in much more detail before deciding anything final.

[@MG-qo5ge]

I've had one for the last 10 years works perfectly no issues the heat pump pulls 660 watts I have also have also a heat pump for house heating, the logic of this is I prefer to to run 660 watts for hot water opposed to run the larger 2000 watt house heating compressor though both are run on off peak electric

[@TimAndKatsGreenWalk]

Good to hear. I'm looking forward to getting mine installed soon, hopefully.

[@MG-qo5ge]

could suggest to place in garage with an air filter over the intake drawing air from the garage via a transfer grill to outside and as the discharge air is pretty cold how about feeding the discharge air to outside in winter and via a "T" and damper duct the air inside during the summer cools the house down if you have that problem could be considered "free cooling" Oh well just a thought.@@TimAndKatsGreenWalk

[@twelvebears1971]

The thermal stratification of Mixergy cylinders really makes them stand out from the others. Obviously if you need to use a lot of hot water in one go it won’t be an advantage, but if you just want a couple of quick showers, it really will.

[@TimAndKatsGreenWalk]

Yeah, for those occasions when you need a quick boost it's a handy feature to have available.

[@FlatToRentUK]

If you're drawing air from the room in which it's located then does this not have basically the same problem as you describe if it's drawing air from the loft? I suppose somewhat it depends on your house configuration. Our garage isn't attached to the house so not an option for any of this kit. We have an airing cupboard though where there was a hot water cylinder when we moved in but we got rid of it for a combi boiler. This would be quite well located to pull from the loft and vent to the outside. Our upstairs is always a fair bit hotter than downstairs and some of this must go into the loft so be nice to suck some of that heat back down again! That would then probably push me towards the one that makes the least noise so soundproofing might be needed.

[@TimAndKatsGreenWalk]

Yeah, if the air is coming from the room the cylinder is located in (e.g. airing cupboard) then that air will need to be replaced from somewhere, so it'll likely come from the rest of the house, which in turn would then get drawn from outside, so you'd cool your house down in the Winter. That's why a vent to outside is necessary for input as well as output. If you're drawing the input air from the loft then it'll cool the loft in the same way as that air will get replaced from the outside, so you're likely to indirectly cool your house too in the Winter (since more heat will rise into the loft to replace what was removed by the heat pump, as I explained in the video), which isn't really a good thing as you then have to heat your house more. You may suck the heat back down but you'll then have a colder loft so the heat will leak back upwards quicker due to the larger temperature difference between your house and loft. Having said that, if you have plenty of loft insulation, and your loft is well ventilated, then your loft is unlikely to be much warmer than the outside air anyway in the Winter, so drawing from the loft might not make much difference to your house heating load, or indeed the performance of the heat pump in the Winter. If your loft is warm in the Winter I'd suggest extra insulation in any case! In the Summer the loft is probably warmer than outside due to the sun heating it so you might gain some benefit with with your cylinder achieving a better efficiency (due to the higher input air temperature), so I think the benefit comes in the Summer rather than the Winter. It really comes down to what's practical regarding the vents. If it's more convenient to have the input vent coming from the loft then that's what you should do. Just as long as you always vent back outside! As for sound, all of them have similar noise levels so you would definitely need some sound proofing if you plan on installing one in an airing cupboard.

[@FlatToRentUK]

@@TimAndKatsGreenWalk I suppose it'll come down to a rough calculation on which way is the most efficient, possibly factoring in other considerations. Obviously we'll be using hot water all year round so will constantly benefit from improved performance there through drawing in hotter air to start with. And pulling hot air from the loft so more can escape from the upstairs might be a small relief during hot summers! Thanks to you though I'll probably install an air-to-air (if I'm not then why bother looking at heat pump water cylinders?) which will hopefully make those hot periods more bearable anyway. I wonder if our best solution is to just use the air in the room and vent to the outside. There's a small radiator in the airing cupboard but the main source of heat now is the solar battery. Installing that has actually turned it back into a proper airing cupboard again! So could make sense.

[@TimAndKatsGreenWalk]

@@FlatToRentUK I'd still consider having the input vent coming from the loft rather than the room itself if you can. These cylinders consume vast volumes of air so you don't want to find you're sucking up all the air from the house. Good luck with your plans, regardless of what you decide in the end!

[@lyracian]

My plan was when I replace the boiler with a heat pump is to put a Heat pump hot water cylinders where the boiler currently sits in the kitchen. It already has a vent to the outside and most of our water usage is in the kitchen or bathroom directly above it.

[@TimAndKatsGreenWalk]

If you're planning an A2W heat pump heating system then it will come with its own cylinder, so you wouldn't need a heat pump cylinder. Or do you mean you plan on getting an A2A heating system?

[@MrKlawUK]

if they take that long to heat a full tank that would make me think they’d either have to run long during the day; I’d size based on only heating overnight off peak because they can’t recharge fast; or more heavily consider mixergy as it can always provide hot water and doesn’t dilute compared to others

[@TimAndKatsGreenWalk]

Usually they wouldn't be heating from fully cold, so the reheat times should be less than those values but yeah, it's still several hours, probably. Even so, that's a big plus point for the Mixergy.

[@Eggnog3000]

Notice that the Vaillant model is now discontinued on the Vaillant site? The mixergy has mixed reviews...I'm in the exact same position as you... Think we're going to go with the Daikin....

[@TimAndKatsGreenWalk]

I think you may have spotted the auroSTOR not the aroSTOR? The aroSTOR isn't showing as discontinued: professional.vaillant.co.uk/for-installers/products/arostor-domestic-hot-water-heat-pump-58880.html As it happens I believe the Dimplex cylinder is actually the same as the Vaillant one (not sure which is the original). I hope the Daikin works well for you.

[@Eggnog3000]

@@TimAndKatsGreenWalk Ha, yes...was looking on my phone and misread it...OK.. have you seen The EV Puzzle's review of the mixergy cylinder? That's what's putting me off. To be honest I can't find a great deal of info on Air Source Integral Cylinders as all the searches come up with cylinders for conventional Heat Pumps! I just need to make sure I don't spend 2K on the wrong one...Got a couple of hundred litres of oil left then it's decision time! Have you ordered the Mixergy yet?

[@TimAndKatsGreenWalk]

@@Eggnog3000 I did see Nigel's review, yes. I think he's quite keen on it now from his more recent videos after some initial teething problems. There are no reviews of the iHP so far that could find, presumably because it's not out for general sale just yet, but I should have some more info to share on that soon as we're going to visit the Mixergy office tomorrow (keep that under your hat!). I totally understand your reluctance to commit without as much information as possible. I hope to be able to add to the pool of knowledge with this channel.

[@Eggnog3000]

@@TimAndKatsGreenWalk OK great, looking forward to the content... Only realised that you need planning permission for the external units from these comments too! What a nightmare... Hope it's going to be worth it!

[@theholyfamilyallsaintscath2899]

if you fitting it inside your garage , i think you will benefit from the higher ambient temperature inside the garage during winter , by drawing the air from inside the garage. This way the COP will be higher . In summer you can draw from out side it you want to.

[@TimAndKatsGreenWalk]

But that heat drawn from the garage would then be replaced from the house which would then increase the load on our heating system. Sadly you don't get something for nothing in that situation.

[@xxwookey]

@@TimAndKatsGreenWalk Right, but at least in principle this '2-stage' (2 small steps) heating should give better efficiency than both the heat pumps working from cold outside air. (I think - I'd have to do some sums on pump losses to be sure). Making 50C hot water from 20C internal air will be a lot more efficient than making 50C hot water from 3C external air in winter. Of course on hot summer days when it's hotter outside than in then an external supply will have lower delta-T and thus be more efficient. Yes you need to make that 20C air from 3C air in the room heat pump so the question is does 3C->20C + 20C->50C use more energy than 3C->50C? I have the extra consideration that my house has an MVHR system so is quite airtight and adding more external vents (which will also be thermal bridges) is best avoided. Interesting that you didn't include the ecocent, which is the one of these that has been around for about 15 years already.

[@TimAndKatsGreenWalk]

@@xxwookey these cylinders consume *vast* quantities of air. They'd empty your house of warm air in minutes leaving your home very cold indeed with all the cold air that would then be drawn from outside to replace it. You definitely don't want to be consuming air from inside your home.

[@xxwookey]

@@TimAndKatsGreenWalk But that's how the ecocent has worked for years and the user I know is very pleased with it. Heating up a hot water tank is a few kWh/day (depending on how much water you use) so whilst it moves lot of air it's only adding that same heat load to your CH, surely? In most UK houses the heat load is much larger than the hot water load. Only when you get to passivehouse levels is the hot water load similar-to/larger-than the heating load.

[@TimAndKatsGreenWalk]

@@xxwookey you will not gain overall efficiency by consuming the air in your house for the purposes of heating your hot water. Even if your hot water cylinder works more efficiently you'll lose more than you gain by making your heating work harder. You don't get something for nothing. At best you'll break even but that is extremely unlikely. If you could make heat pumps more efficient by doing a two step process like this then they would all work that way already.

[@MrKlawUK]

not sure the loft would cool like that. Assuming its already a cold roof any heat from your house is leeching rather than pulled so I don’t think it’d change. You may end up cooling the loft space by a degree or so but I don’t think it’d affect your main house

[@frankcrompton2172]

It won't cool , it's a cold loft .

[@TimAndKatsGreenWalk]

Not much, perhaps, but you are removing some heat, which will get replaced somehow. Conservation of energy. But it probably makes little practical difference, I agree.

[@colingoode3702]

Yep, don't know why Daikin & Mixergy went for R134a & the Daikin 1 kg refrigerant charge must be wrong for such a small close coupled system. The average refrigerant charge in a large fridge freeze is 100-400 grams so 1kg is way too much imo. Sound Power level data is the noise level taken at the source e.g. next to the unit in question. Sound pressure level is at a specified distance in a free field with no barriers & is lower than the Power level because sound levels decay over distance. Any barriers between the source of the noise & the measured distance will have a reduction effect on the source noise level. So if the heat pump was inside an airing cupboard the walls of the cupboard would reduce the noise level outside of it. If the cupboard walls were acoustically insulated then this would reduced the noise level even further. That said, I would still not recommend putting one of these HP cylinders in an airing cupboard with bedrooms bedrooms nearby. The Garage or the loft would be a better bet. I was looking at my loft for one of these (in place of the gravity cold water tank) but I have a small trap door which means extra cost to enlarge it. The smaller diameter Dimplex 170 might be an option but probably not enough water volume for a 4 bed house. My garage is rammed but is a better bet & easier to install a cylinder like this albeit connection to the mains / hot water pipework in the house more of an issue. Decisions, decisions.

[@TimAndKatsGreenWalk]

Yup, my preference is for the garage and thankfully we have space there. It will take some minor rearranging but nothing too troublesome, hopefully.

[@clarkfinlay78]

It will very much depend on the cost of the mixergy it is certainly the one I am hoping to go for but as its still to be available for sale it is a worry.

[@TimAndKatsGreenWalk]

Yes, indeed. We should find out soon as I hear it'll be available shortly. More on that as I find out the details.

[@clarkfinlay78]

@@TimAndKatsGreenWalk The only pricing I have seen is about £900 more expensive than the Vaillant

[@TimAndKatsGreenWalk]

@@clarkfinlay78 yup, that doesn't surprise me. Although you could probably get away with a smaller cylinder since you can heat it up more quickly if required, so that might mitigate the cost difference slightly.

[@chrisgavin]

Newbie question here ... If heatpumps can be run indoors and sitting on top of a water tank like this ... Why would we still need such giant heat Air Source pump units sitting outside of our house being exposed to the elements/weather ?

[@TimAndKatsGreenWalk]

Because of the amount of power a heat pump used for heating your house requires. These ones on the hot water cylinders are much less powerful as they only need to heat your hot water not your whole house. For example, hot water requirements would be about 2 kWh per day, but when it's cold outside you might need 30 kWh per day for your heating.

[@chrisgavin]

@@TimAndKatsGreenWalk Thanks. I'd never seen these heatpump hot water tanks before, really interesting. I'm in the process of buying a house with an old oil burning CH system and no mains gas available. So looking around for alternative systems ...

[@kavanobrien6547]

It’s whiskey time guys , my messages need to have a health warning attached to it = need at least a half bottle of whiskey, once again apologies for my stupid questions, have been watching a few channels in regards to heat pumps but yours is the one that makes sense to my simple mind , I don’t have money for solar or battery storage = just don’t have that kind of money, for my situation makes sense to get rid of my gas boiler and go heat pump but makes more sense for me having air to air rather than going air to water with changing radiators size and all that stuff , I live in a small three bedroom terrace house and was thinking about getting a cylinder with heat pump and getting two mini split systems one down stairs one upstairs and get rid of all the radiators plus my immersion heater tank , in my head it makes sense but it would be nice to get your opinion, also with the government grant would I be allowed to have that system or does it only apply to a system such as air to water ? Because I think the system I have mentioned would be cheaper not only to purchase but also to install.

[@TimAndKatsGreenWalk]

Currently the boiler upgrade scheme only applies to air to water systems, so your plan wouldn't be able to benefit from that. I'd suggest getting in contact with Octopus (if you are supplied by them) to enquire about their air to water system installation. For a property your size you might find that it costs almost nothing extra after the boiler upgrade scheme has been applied, so well worth looking into. If you went for A2A plus heat pump cylinder you won't get any grant and it'd probably cost you the best part of £7-10k for that combination.

[@kavanobrien6547]

@@TimAndKatsGreenWalk Thanks for reply , shame it only allows for one system yet the other system would be cheaper without the upgrade to radiators so overall would be cheaper to install, makes me wonder if I as an individual can apply for the grant and then get the system I want and of course supply the receipt to the government so they can see that it was spent for the green agenda .

[@TimAndKatsGreenWalk]

@@kavanobrien6547 I'm afraid it doesn't work like that. The BUS simply can't be applied for with an A2A system, regardless of who does the application.

[@kavanobrien6547]

@@TimAndKatsGreenWalk OK thanks , looks like I’ve got my agenda for 2024 then = want to get rid of gas but on the terms the government has deemed is the green way to go , yet my way is cheaper that sounds logic has been on some kind of acid trip , having paid in for over forty five years with taxes I didn’t say how they spent my taxes I relied on them to spend it wisely, sounds like a crusade is pending. Always a bright side you’ve been introduced to single malt whiskey.

[@TimAndKatsGreenWalk]

I agree, it's bonkers that the grant doesn't apply to all heat pump systems. I hope that will be rectified at some point but as you say, we're subject to the whims of whoever is in charge, sadly.

[@stevenbuil8836]

I would be careful where you locate it in relation to where you sleep as they can be quite noisy when running and they need to run for a long time.

[@TimAndKatsGreenWalk]

I literally made that point in the video.

[@gsum1000]

Immersion heaters don't work in the way that you describe. The heated water rises to the top of the cylinder and, as the stratification between the hot and cold water is very pronounced you can draw off the water from the top without needing to heat all the water in the tank. As far as I can see, the Mixergy tank is little more than an immersion heater with additional control and monitoring capabilities.

[@TimAndKatsGreenWalk]

These are heat pump cylinders. I wasn't talking about the immersion heater heating the water I was talking about the heat pump, which heats all the water in the tank fairly uniformly; there is no pronounced stratification as the heating is spread out over a wide area around the cylinder.

[@HowardBurgess]

Mixergy (either immersion or with integrated heat pump) seem to defy physics by heating from the top down. They do this by putting the heat source at the top, then using a small pump to take colder water from the bottom of the tank and move it to the top. By controlling how fast this pump operates with software/sensors, it can gradually push the chunk of hot water down from the top. I presume it operates slowly enough not to stir up the water too much.

[@chriss4949]

It operates by “misting” the water into the top, minimising the turbulance

[@MagnoliaHouseRye]

Hi Tim & Kat, I have a zero-emission (and very effiicient) Bed and Breakfast down here in the lovely Ancient town of Rye, in East Sussex. I'd very much like to invite you (and family) down for a night for you to review, comment, critique and discuss going from a regular domestic user to "light commercial", with a 34 panel solar array, a 12kw ASHP, 10x Air to Air heat pumps, underfloor and heated skirting boards....oh, and 4x 7kw EV chargers to boot :-) I hope you catch this comment :-) All the best, Javed Khan, Magnolia House Rye.

[@TimAndKatsGreenWalk]

Looks like a really interesting project, Javed, we'll be in touch, just need to work out some plans...

[@frankcrompton2172]

I've worked on heatpump installations and have had an air to water system for over10 years now. Some of your information is very misleading to anyone out there who doesn't understand the technology. A separate tank isn't the best option , because if there's an issue on the tank you have nothing. Also I find your comments about re heating the garage or loft. You either have a warm loft or cold loft , you don't heat it. A cold roof is always pulling fresh air through the sofit vents, so it's using latent heat . Every system has a once a week setting to go over 60° and yes it is needed.

[@TimAndKatsGreenWalk]

I did say if you have an A2W system you don't need a separate heat pump cylinder, I was very clear about that (see 02:53). I don't think that was misleading in any way. Regarding heating loft space, it doesn't matter how much insulation you have some heat from your house escapes into the loft, that's basic physics. If you remove heat from there it will make it colder (even if it was 'cold' to start with) and your house will lose some heat back into it. It may not be much, and it may not make much practical difference, but that's how conservation of energy works. I did also mention that these systems all have anti legionnella cycles.

[@chriss4949]

You dont need 60 degrees , as Tim says 55 is plenty

[@hugorm6739]

U cude let it go tru u loft and make a lem to swise betrine winter and summer,

[@TimAndKatsGreenWalk]

It'll probably come down to what's practical at the end of the day.