My Hot Water cylinder is the WRONG size! What I've learned about heat pump hot water cylinders.

[@grahamwoodier5066]

Achieving the perfect size of hot water storage cylinder is probably even more complicated than you have described. When I swapped my 160L tank for a 200L version with better insulation I failed to anticipate one of the negative consequences. My wife uses our airing cupboard to store bed linen and towels but the shelving is now about 350mm higher up so she has difficulty reaching the top shelf without standing on something. I am reminded of this inconvenience on a regular basis.

[@UpsideDownFork]

Oh yes! I had to trim all of the shelves and reposition them in front of our cylinder. So we have three times as many shelves that are a third of the depth of what we used to have. Skinny little shelves that are accessible at the front of the cupboard made my wife happy.

[@Leo99929]

Interesting observation! I might talk to my installer about mounting the cylinder as high as possible, so that the shelf is under, rather than ontop?

[@UpsideDownFork]

@@Leo99929 It's a lot of weight that you ideally want mounted directly onto floor joists.

[@shuhel02]

When you said 'occasionally we do run dry' that for me was the deciding factor to stick to my efficient gas boiler for the moment until we are forced to move off.

[@UpsideDownFork]

This is not a heat pump issue, this is an undersized cylinder issue. It is very common with gas invented systems too. If you're on a combi then you won't be aware of it. Now that I've mastered the controls and adapted to our routine, we haven't run out of hot water in many months. I was very conservative to start with, trying to eek out every last bit of efficiency but I've relaxed into a better balance of efficiency and comfort now.

[@JOOI525]

Another topic that I have never seen covered. Certainly enlightening and will be so useful for those who are at the point of pressing the button on a new install.

[@UpsideDownFork]

Thanks for commenting! I hope it will be helpful for many people who stumble across this during their journey!

[@crm114.]

Nice overview. We have a similar Vaillant system but with a 300 l Joule cylinder. One thing I’ve found is that changing the offset temperature in the settings makes little difference to the hot water flow temperature. With the hot water temp set to 50 C, the flow temperature still gets to 58-60 C even with the offset value at zero.

[@UpsideDownFork]

Yes, I did some reading on one of the forums and it appears to be the flow rate that the Vaillant heat pumps run at. Because the rate is so high, the offset is rarely relevant apparently. Thanks for the comment!

[@JohnBrophy-z1c]

using eco mode make a big difference to this and consequently to COP

[@UrbanPlumbers]

it is all to do with the power available from the unit and coil size. Basically, your coil is too small to be able to take the power from the unit once the cylinder gets closer to the target. You should still run offset as low as possible, but you need to watch for cycling. If you have a larger coil such as a Newark HG cylinder with 6m2 coil and a small heat pump set to eco (5kW) to limit the output to 4.5kW you can run offset at 0c and the flow will only overshoot by few degrees. Try that on a Vaillant cylinder (tiny coil) and it will overshoot more. Try it on bigger heat pumps 7-10kW and the overshoot be even more. Always keep offset low.

[@andyballard1883]

Thanks for another great Video, it's great when people are happy to share missteps as well as successes. I had two thoughts out of this firstly there is also the issue of oversizing, for example in my case I am a single occupant in a 4 bed house so my own needs would be catered for with a 100 ltr cylinder and this would be most efficient from a draining the tank daily (ish) perspective. However in planning the system I need to consider if I ever sell my property it is much more likely a family of 4 would buy it and hence there requirement would be a 250ltr Cylinder so I would need to drastically oversize for that probability. I think there is a easy/neat solution to this. Market a cylinder type that has two chambers insider of say 2/3 and 1/3 capacity and have a physical lever mechanism on the outside of the tank that allows a flap to slide open in the division to allow use of the smaller top chamber when needed.

[@davideyres955]

Have a watch on the heat geeks video on their cylinder and take a look at the mixergy tank as well. Basically you get minimal mixing in water at different temperatures so a boundary layer. So the mixergy one actually heats from the top rather than a standard tank that heats from the bottom. So you decide what amount of water you want to heat.

[@UpsideDownFork]

Yes, great comment! I have seen on one of the forums that someone has installed 2 x 150L tanks and has some valves that they open when family comes to stay and close them off when it's just the two of them at home. I'm not sure how they combat the stagnant water that sits in the second tank, but it's interesting to see innovation!

[@geoffreycoan]

Great walkthrough, thanks. I think we probably have the opposite, a 250L cylinder in a large house but with now just 3 of us living here. I found that our hot water was being heated by both the heat pump and the immersion heater, the immersion wasn’t just being used for the anti-legionella cycle 😢 Turned immersion off so its heat pump only, turned tank temp down to 48, increased the hysteresis to the max possible (4 degrees), hot water just once a day overnight and I think I’ve got the optimum configuration now. Its usually 1-2kWh to heat the hot water a day which feels like a good result

[@UpsideDownFork]

Glad you caught that issue. Immersion heaters being used unnecessarily appears to be a common issue in the heat pump group on facebook. Sounds like you do have it dialled in nicely!

[@jameswestcott4191]

Goes to show the complexities of new home heating technologies. Whereas a gas boiler could easily accommodate everyone’s needs, the design & usage of a modern system is more critical even to get cost parity let alone save money. Great to see people innovating and trying out different solutions.

[@UpsideDownFork]

Yes, I think these things will converge as heat pump system design matures.

[@jchidley]

Thanks for the insight. We're also a family of 5 with 2 bathrooms. For the last few years, I had been measuring how much hot water we use per day, on average, with our combi boiler. It's about 250l at a 55C flow temperature (my wife and son love extremely hot showers). I wish I had known about the heat geek cylinder: I picked a 300l solar cylinder (the solar versions have 2 heating coils that I will combine into 1 larger coil). It would probably have been easier with a 300L Vaillant but hindsight is perfect. I should be plumbing my heat pump in shortly so your comments about control will be very useful. I also have already plumbed in a Waste Water Heat Recovery (WWHR) from Recop - the side benefit is that it reheats the cold water used in the thermostatic valves so perhaps I will not have to run the water at 55C. Given what you said, I'll be aiming for 1 reheat a day at 48C, or less. Currently I am using the internal 3kW immersion. This heats up the top third of the tank to a toasty 62C. This covers us for a shower and a bath and reheats within an hour.

[@UpsideDownFork]

Sounds like a great plan. Have you attempted to reduce DHW consumption? I know it can be a contentious topic and we have to pick our battles! 250L @55C isn't high for a family of five, but it's not low either. Our smart shower timer function has helped us dramatically cut our usage. It is now set to a max of 6 minutes and then will turn the shower off. 6 min is now the maximum, not minimum shower length allowed in our house. It's amazing how easy it is to change human behaviour sometimes. Also, aerated shower heads has helped a lot. Good luck and I hope the installation continues to go well for you.

[@richardpratt5251]

As a short term fix you could increase the store temperature. Our 3-bed, 160 sq m property had an oil boiler which was replaced 11 months ago by a 7kW aroTHERM Plus system with a 250L uniSTORE cylinder. There are normally two adults living at the property and we find that an overnight cycle to 52 degrees provides all our hot water needs for the day. According to the myVaillant app, our hot water electricity consumption so far for 2024 is 458 units at 9p/unit (8.5p since 1 July) and the COP is 4.2. When my son and his family came to stay, I simply switched to manual for the duration to ensure there was hot water at all times.

[@UpsideDownFork]

Yes, that's good advice and exactly what we've been doing. It's working so far.

[@dominicgoodwin1147]

An external brazed plate heat exchanger has a massive surface area compared to any coil-in-tank transfer. I got a Vevor 100 plate exchanger for just over £200 new on eBay and it is absolutely amazing!!!! And a dumb tank is so much cheaper than a complex tank.

[@jameswestcott4191]

Do you need a tank that can take a heat exchanger or can it use the inlet/outlet feeds?

[@nickflynn666]

Uses the feeds, mounted externally to the tank.

[@B0jangle5]

Probably easier to install the tanks too? Those large pipes in the tanks must weigh some.

[@dominicgoodwin1147]

@@B0jangle5for me it was partly about price, partly about performance and partly about control. My target price was £1 per litre for storage by buying used tanks and I ended up paying £1100 for 1300 litres of stainless steel storage. The performance of the plate heat exchanger is amazing. It can easily transfer my 15kW and cost just £218. The flow constriction is minimal, unlike the pathetic 22mm primary pipe that runs through lots of indirect tanks. You want to get heat away FAST from the condenser of your heat pump for efficiency, and this lets you do that. The only annoying thing about it is that the ports have 1.1/4” NPT threads (US national pipe standard, tapered). I couldn’t find an adapter anywhere. I’m using a rubber adapter with jubilee clips until I find one). The last thing is control. Things get much more versatile if you can choose flow rates of your primary and secondary water flows.

[@Aphova]

That's a great idea, thanks for mentioning it!

[@michaelridley2864]

Thanks very much for sharing - great content, and all in one take!

[@UpsideDownFork]

Glad you enjoyed it! One take is what seems to work for me.

[@Ben-gm9lo]

Thanks for the video, sorry to hear you run out of hot water from time to time. It is very good of you to share your concerns with us all. If I may make one small point though on your interpretation of the data from the MCS site about required cylinder size for beds/baths. From memory you have a 7kW Aerotherm ASHP. By going straight to the 3-6kW hot water command column on the MCS table you are perhaps assuming that you are only getting 7kW of water heating with the ASHP running at max. Of course, this is incorrect as the ASHP output is dependant on various factors, but is rarely just the rated output. The Aerotherm 7KW ASHP has an output of over 8.6kW at 40 degree flow temp, according to the Heatpunk website analysing my system. This might not be absolutely precise, but the general gist is you will get a lot more than 7kW for most of the year, especially when the cylinder is cold and flow temperatures are lower. For this reason, I believe you should probably split the columns of the MCS chart for analysis of your system. It still says you don't have a big enough cylinder, but it does reduce the discrepancy. Having gone through your stage of parenting, I would say that your boys will be teenagers in a few years, so their water consumption for washing will then plummet, removing your consumption issue! Small mercies of grubby teenagers.

[@UpsideDownFork]

Yes, you're quite right! The badging and labelling of these Vaillant components does my head in! Labelled at 7, but easily producing in excess of 8... Thanks for the reassurance. My oldest boy is currently a clean freak, the other two are happy to be covered in mud. Everyone tells me that boys get easier and girls get more difficult. I'm praying that's true!

[@BremerFischkoop]

There is a certain heat loss by the cylinder. I putted an extra thermal isolation around the cylinder to stretch the time to reload. And I prevented the warm water pipe from micro circulation. That is when hot water can go up in the pipe and leaves the cylinder, that cools down und streams back into the cylinder. In some installations you can have a constant stream of hot water in exchange to cold water within one pipe. The same happen to my heating pipes. Now they go straight down to the bottom end then again upwards to the heat pump controller. You can feel these temperature losses circulations by touching the pipes by hand. They should be cold when the heat pump didn't run for an hour.

[@SimonRGates]

That's really useful, I hadn't considered that 300lt might be an advertised size rather than volumetric, though I'd guessed the coils would take up some space. A quick back of the envelope suggests that my partner can use 135lt of 40 degree water in a single shower. Add in the two teenagers and we're going to need a bigger tank... 275lt useable minimum.

[@UpsideDownFork]

Shower head makes a HUGE difference here. You can do the bucket measure method to know exactly where you are with flow rate etc. Good luck!

[@normanboyes4983]

She would use nowhere near that amount - if the water was fffreezing.

[@UpsideDownFork]

😂​@@normanboyes4983

[@nickflynn666]

You might want to try a water waste heat recovery system in both your bathrooms. Some of them are silly prices new but there are sometimes bargains on ebay. Even new it would probably be cheaper than a new tank to install and will save you more in energy costs I think.

[@UpsideDownFork]

I did have a page in my spreadsheet to calculate if one of these would even return on investment. The answer was no, by a long way. BUT that was for new units and having to endure substantial building work in one of the bathrooms to be able to fit it. I calculated that a house with a single bathroom would benefit more quickly and especially combined with a bathroom refit anyway, the labour cost becomes negligible. I didn't consider finding any bargain units which would change the sums dramatically. They are certainly the future, even though their effectiveness is quite limited.

[@serraios1989]

Megaflo 250lt with system gas boiler. If our three shower rooms will be used at the same time, I just push the one hour boost button, before going in. The cylinder has never ran out of hot water. Last year I was thinking to remove the boiler and get a heat pump. The deal broke when all quotes included a new cylinder and I’m happy with our decision to stay as we are for now

[@UpsideDownFork]

You could keep your cylinder and run a heat exchanger to make it efficient for connecting to a heat pump.

[@serraios1989]

@@UpsideDownFork Interesting point. I received quotes from three installers and a heat exchanger was not mentioned at all. They all said to throw a five year old cylinder in the skip. I just couldn’t accept the waste. Moreover, from a bit of quick research I did at the time, the kw rating of the megaflo coil was superior to the proposed cylinder, but I appreciate this needs further evaluation

[@trailblazer7108]

Sorry to hear mate, hope you get that refund, it’s well deserved. They should have advised you better. Thanks for letting us know about this.

[@UpsideDownFork]

Thanks 👍 It's a first world problem but if by sharing it prevents anyone else experiencing this, great!

[@sdtunstall]

The heatgeek cylinder (works in reverse, cylinder stores hot water as a battery and then DHW picks up heat from it via a coil of piping running through it) seems to be the solution for many showers a day whilst taking up a tiny footprint. Well worth looking at even if you don't plan on changing anything, just for content for your channel.

[@aymerichousez1005]

Are you sure of that? My understanding is that the super cylinder from heat geek was just a conventional water cylinder with a massive heat exchanger to make it efficient.

[@sdtunstall]

​@@aymerichousez1005 kzbin.info/www/bejne/l2K7eHWjd7GIpKMsi=BOU2LktPI6boHSgt I'm referring to this video and yes, at 9:43 he explains he reversed the way it works so DHW runs as a coil through the hot tank which itself is heated by the heatpump.

[@UpsideDownFork]

Yes, I've watched the recent DHW videos from heatgeek with much envy!

[@wardy89]

They have 2 cylinders the super cylinder which is a normal cylinder with a very large coil (my parents had one installed a couple of months ago) and the new one that’s not available yet which operates as you just mentioned

[@UpsideDownFork]

@@wardy89 They really should work on some better branding. The "HG Series Cylinder by Newark Cylinders" has room for improvement. Then of course there is the newer "Heat Geek Mini Store XS-XL by Newark Cylinders" Why they've chosen to label the sizes on these as Fat, Tall, XL, XS etc is beyond me. What's wrong with labelling them by their capacity?

[@DawitTeklu-zi4lt]

Hi buddy - love the vid. Can you confirm what type of heating you use? Do you think installing underfloor heating would help?

[@UpsideDownFork]

I'd recommend you have a look at my heat pump playlist as i've covered this many times before. kzbin.info/aero/PLxiY5khGACu3S5XxEI8_bhkX6H8DOR2VW&si=0Dq7kbXZCd1EM-if In summary, we have stuck with wall mounted radiators for cost reasons. Underfloor heating will typically help the heat pump to run slightly more efficiently but the main difference is the comfort factor really. If you have the funds and can deal with the upheaval of retrofitting the underfloor system, this it is the ultimate luxury but it won't help your heat pump efficiency that much.

[@bryanhindle8307]

Octopus use 50L per bedroom +50 to calculate tank size Which works out to 250L. There is only 2 of us so we only heat tank on Wed/Fri to 47° and Sun to 55°.

[@martynscott1227]

The minimum temperature at cylinder is 55 Deg C to guarantee legionella is kept under controlled.

[@bryanhindle8307]

@@martynscott1227 With our old tank we set it at 50° for the last 20 years and I've lived to tell the tail.😂

[@UpsideDownFork]

Sounds like you've got it set up nicely! Thanks for sharing that Octopus are going above and beyond the MCS guidance.

[@Gazmaz]

Have you watched the recent heat geek vids about the hot water tanks they’ve designed, might be worth a watch.

[@UpsideDownFork]

Yes I have, with much envy! 😁

[@tonyfrewin4822]

Interesting video. Is it easy to top up from immersion heater during solar export periods or is that a non starter?

[@UpsideDownFork]

It could be done but only at 100% efficiency, instead of the 360% efficiency of using the heat pump.

[@Leo99929]

I've been thinking about this because we have two adults in the house but it's technically a 3 bed, so size for 4 people. And I do have two adults over to stay from time to time. 200L should theoretically be enough, but I'm tempted to go as big as will fit, because then I can lower the storage temp which lowers the heat loss to the room, meaning the house will be less hot in summer, and the heat pump will have a better COP whilst filling. It will just take longer to heat the cylinder if and when I do empty it. And as you said, I leave some efficiency on the table if I don't empty it. I'm thinking too big is better than too small? realistically it's not going to be more than about 25% wrong either way, and I think the failure modes of bigger are better than the failure modes of smaller?

[@UpsideDownFork]

Heat loss to the room is so small and marginal, I would discount that as a factor if I was you. If you want efficiency, you want to focus on coil size rather than capacity. If you want the luxury and comfort of never running out, go larger. If you regularly only use half of your tank then your heat pump will always start heating from a high start point, once again losing efficiency. Try not to overthink it too much. Our heat pump can reheat the cylinder so quickly anyway that it's not really an issue, even when people come to stay. It takes a couple of seconds to switch it from timer to constant reheat and. Designing your heating system and your cylinder for 95% of the year is the way to think, rather than anticipating the 5% of times when you might need to be adaptable.

[@aymerichousez1005]

I have a 290l Joule cylinder for a similar size house. I operate it on hysteresis, not on schedule and with a target temperature of 43 degC. It usually does 2 cycles per day and takes 30 minutes to recharge. It is debatable to claim installer negligence because he will argue that you can run your DHW at higher temperature. Depends on what scop was sold on the contract, but even tho, these are indicative, not contractual values.

[@UpsideDownFork]

Thanks for commenting. Good to see you're still here with a water temp of 43. The anti legionella gang will be on their way with a warrant to turn your store temp up to 55! 😁 I guess you need a lot of water to have a 290L tank on hysteresis?

[@aymerichousez1005]

With 43 degC for a family of 4, we are using the capacity of the tank every day so no much risk of legionela. Great video from heat geek about this. kzbin.info/www/bejne/pXvIqpaVmKx8g7csi=u08JRVdVGNuxUhmY

[@justinhumphreys5230]

Great videos keep them coming On tracker and wondering about switch to agile - I have a large heatpump Is there a telegram agile price notifier like the tracker one Cheers

[@UpsideDownFork]

Thanks for commenting. I use the Octopus Compare app which gives me a push notification at around 5pm. I'm sure there must be a telegram notifier because agile is much more popular than Tracker is.

[@rolandrohde]

My hot water COP is also relatively low on the Vaillant with Unitower Plus, but it's OK. In the warmer months the actual energy consumption for hot water is around 0.8-1.5kWh per day and about 2kWh for the Legionella cycle. I don't see much of an improvement in hot water performance between 15°C and 30°C ambient temperature, but as long as the actual energy consumption isn't too high I don't care much about COP. Heating is also OK. The COP isn't great since my house is well insulated and the heating only needs to run when it's actually cols outside, but the actual energy consumption and cost have been pretty low, so I am not complaining.

[@UpsideDownFork]

Thanks for sharing. Your observations are very much in line with my own!

[@barriedear5990]

We run legionella cycle at 12.30am on Intelligent Go, and reheat as required, usually not until early afternoon. 6 people at home. Comfort over absolute efficiency, as no-one has set routines. Installing battery shortly, so will stop the legionella cycle. Changing charging offset makes no difference, will need to check if on eco mode, which would hep for summer months, but might need to be off for the coldest months.

[@UpsideDownFork]

@@barriedear5990 I've never run a legionella cycle and kept the tank temp around 50 degrees for the last two years 👍

[@Group51]

Remember the first eco thing to do is reduce. (fair play though I see in the video you've tried this). Before I got my SunAmp (no room for a big tank) I spent £300(!!!) on an Hansgrohe aerated, "ecosmart" low water shower head. (40% less water when showering). All other hot water use in my house is minimal. Yet to run out of water. MyVailant says my Heat Pump efficiency with 70C flow is 4.5 (summer 2024).

[@UpsideDownFork]

Nicely done! I've attacked both areas of configuration and also human behaviour. Fortunately our smart shower has various settings that help but one of them is the timer that gives 6 minutes and then just turns off. That's helped adjust our behaviour!

[@johnrush3596]

We are a family of 5 and have a mixergy 210lt tank with a plate exchanger and have not as yet been able to run it out of water. I will admit we do not yet have it feeding a shower, it is only feeding the main hot water for sinks and a bath, but we have easily managed 2 sizable bath times in a night regularly without running out. I would look at any of the units that use stratification to maintain temperature as they seem to work really well. Mixergy is not the only brand that uses this technique.

[@metalhead2550]

It's worth mentioning that the Mixergy tanks use plate exchangers so you will have an actual usable hot water volume of 210L rather than the 172.5L from the Vaillant 200L due to the volume taken up by the coil (as stated in the video) so that's the best part of 40L which is almost an extra person's allocation :)

[@UpsideDownFork]

Thanks for your comment. Heatgeek has some interesting videos about your mixergy tank, both for good and for bad. I'd like one just for the control freak in me and the access to more data!

[@effervescence5664]

Hot water generally is the biggest issue with heat pumps from an installers pov. Generally we try to put forward a larger cylinder so for yourselves I would of spec'd the 300 not the 250. This is because we have found that when people go from a fast cycle time from a conventional fuel source to a heat pump larger families have issues managing their water usage. It's normally better to increase the volume to keep the efficiency and have people not run out but we have to take into account space, cost and energy/water wastage. With a conventional heat source it's very easy to have a small cylinder with a faster cycle time because the temperatures are higher, around 17-25 minutes in some cases but you can quite easily double that once your heat source is a heat pump. I will say that if anyone has daughters (especially teenage ones) it's a better idea to size up, if you have boys it's less of an issue.

[@UpsideDownFork]

Thanks for sharing, that's great to hear!

[@bamber119]

After watching this I did a little Bit of digging myself, my Cylinder is 200l but there's only 3 of us at home. Would have got away with a 160l tank which is the smallest Samsung tank. I'm not about to pull it out and replace it though. lol

[@UpsideDownFork]

Possibly better to be a bit over, rather than a bit under!?

[@wardy89]

In fairness at at store temperature of 48c you are still relatively low, yes it would effect your COP but you definitely have head room to increase that further.

[@UpsideDownFork]

You're definitely right!

[@normanboyes4983]

Good overview - of course rules of thumb are invariably rules of dumb. Leaving aside the technical nuances - there is always the option of educating the family to use less hot water by adopting the ‘submariners shower’ technique. We all waste so much water and they do say you only truly appreciate the amount of water you are using if you have to carry it . Challenge the family to carry 25 litres of water a 100 yards.😉

[@UpsideDownFork]

Great perspective! We did all go on a crash course when we moved into this house 2 years ago. Previous place had a combi boiler and i'm ashamed to say that we took the unlimited hot water supply for granted. This house had a 140L cylinder with the old boiler. The smart shower timer has helped a lot!

[@typxxilps]

The coil has to be big to have a huge surface for a faster heat exchange therefore the incresasing losses from gros to net capacity. Of cause 250 would be a lot better for you but again not really considering that 211 L is again below your "estimate" demand. But keep in mind: bigger sounds better but it comes along usually with higher heatlosses and those are Watts in a 247 use case which most people are not able to calculate. RULE OF THUMB: in a 247 use case any watts used mean an annual consumption in kWh of 9 times the watt figure If your cylinder is for example using 30 Watts less than the bigger one then you are saving 9 x 30 = 270 kWh p.a. Bigger cylinder means always more standby consumption and the good ones will be at 33 Watts (we have a 270L cylinder with a heatpump on top) and the bad ones might have a 160 Watt figure. 130 Watt more means 9 x 130 = 1.170 khW per year of additional losses cause the heat is leaving the water and therefore has to be invested again. 1170 kWh equal in a perfect oil burner roughly 117 Liter Oil - if you consider 20% of losses going through the chimney than 1170 kWh / 85% = 1376 kWh divided by 9,8 kWh per L oil = 140 Liter more oil And that is a figure everyone can imagine, a tank of 140 Liter Oil or 14 buckets of 10 Liter just for the missing insulation. 1376 kWh per year sounds not like that much until you do the math.

[@UpsideDownFork]

Where do you get that equation from? Vaillant Unistor 200L cylinder rated at 1.22kWh heat loss over 24 hours. Vaillant Unistor 250L cylinder rated at 1.41kWh heat loss over 24 hours. 190W difference. Are you then diving this by an hourly figure? 190/24 = 15.83 watts. 15.83x9 =142.5 I find it incredibly difficult to believe that the next size up cylinder would cost an extra 142.5kWh per year. Our total annual DHW consumption is only 598.2kWh. Also worth considering that the coil surface area will increase from 1.4m2 to 2.4m2. There is some evidence to suggest that this not only shortens reheat time but that the DHW COP will increase by approx 0.5, all other things being equal.

[@lib_f]

The usable tank info is interesting... I have a custom tank so not sure if the 150L stated is usable or excluding the coil. Doesn't matter for me right now because nothing bigger would fit in the cupboard and the cats don't shower, but good to know, especially with a 3.5kW HP. The large coil is meant to be mean a fast recharge.

[@UpsideDownFork]

Great stuff. Hope it's all working nicely for you so far!

[@philreilly6959]

While I was watching your video (again), there was an 'Everything Electric Show' video below it. Their guest was Mat Ferrel. When I first looked at it, I thought you were their special guest. The likeness is very strong. Anyway, thanks for the video. I think I commented before that I'm just waiting for an installation date from Octopus., so all information is useful. You might be able to answer a different question for me. I've already had solar and a home battery for 18 months. My gas consumption for 2023 was (thanks to the solar and battery) 10200kwh. I've watched a video by physicist Michael de Podesta, in which he said that a rule of thumb way to decide what size heat pump you need, is to divide your annual gas usage by 2900. This would suggest that I need a 4kw pump (3.52, to be precise). Octopus are going to fit a 9kw pump. Do you think that's too big. I watched lots of Heat Geek videos and he says that having a pump that's too big really makes the efficiency suffer. What's your view?

[@UpsideDownFork]

I do like Matt Ferrell so i'll take that compliment! I've watched all of Michael's content and he has a lot of good information presented. A rule of thumb is just that. I wouldn't hang on to it too tightly. In my case, dividing by 2500 would be the most accurate way to calculate the heat loss from our historical gas usage. 12270kWh gas consumption = 4.9kW heat loss. We also added central heating to our kitchen diner which was previously heated by electric underfloor heating. This area added an extra 1kW to our overall heat loss, making a total of 5.9kW and pushing us towards the 7kW Vaillant unit. Putting that aside, it does sound like Octopus are massively oversizing your heat pump. I think the 9kW is the worst of all the Daikin units as well. From memory it is the same physical HP as the 11 & 13kW units but different software. It means that it cannot modulate down very low and will cycle a lot more. I would first of all check the heat loss calculation that they've carried out. Second of all I would push for the 6kW or 8kW Daikin units which can modulate down a lot lower than the 9kw unit can. The 8kW Daikin was the first option we were given, but it wouldn't have passed the noise test in our case. The Vaillant is just a tiny bit quieter.

[@alanc1406]

Mcs is just for guidance . occupancy and age(teenagers multiply usage by 3) dictate hot water consumption within a household

[@UpsideDownFork]

Thanks for the comment!

[@asabriggs6426]

Strange that the Vaillant cylinder is by the volumetric capacity rather than the DHW capacity. This is in marked contrast to the heat pump power output rating which is on a worst case heat output. Good luck with chasing up British Gas.

[@UpsideDownFork]

Yes, I agree! Labelling and badging does my head in!

[@edwardpickering9006]

The MCS guides are very misleading. The problem is that an MCS accredited installer HAS to follow them, even if they know it might not be the best option... I have the other end of the problem as MCS would insist that I get rid of my 2 year old hot water tank (which provides plenty of hot water at 45 degrees all year round) and doesn't take into account that I can heat most of it off an immersion heater from Solar PV. It's really put me off getting an ASHP under the MCS scheme, total waste of perfectly good equipment. That said if I did replace the tank it would be with a Mixergy one...

[@scottwills4698]

I have a Mira shower which measures water usage. My daughter uses 180 ltrs 🤦🏻‍♂️ My heat pump reheats, as I have a battery it’s not a big deal.

[@UpsideDownFork]

180L?! 🫣 How are you still sane?

[@stevemorris1881]

Could you install a second cylinder and have 1 for each bathroom

[@UpsideDownFork]

I guess that is a possibility. Unfortunately we don't have the space available for that.

[@stevemorris1881]

I watched the heat geeks and they had developed a small cylinder that could fit under/in a kitchen unit. I know the pipe work would a nightmare but something to think about. Hope it all works out for you 👍

[@pmbpmb5416]

Would Increasing store temperature considerably and just one cycle on cheap rate help ? My problem is capacity needed for whole house full I need biggest cylinder , when there are only two of us which would be most of the time we have the big cylinder , inefficient, although am going for the new heat geek one which I am hoping will help . But without such as you flagging this people won’t think about it .

[@UpsideDownFork]

Yes, that's what we've been doing for the last few warmer months. Higher temp and one cycle on cheap rate. We'll keep experimenting to find the sweet spot. Glad it got you thinking.

[@pallsmortion4750]

I told you it was too small, it should be around 300 litres

[@UpsideDownFork]

Unfortunately the tank had been installed before I put any content on KZbin at all.

[@briangriffiths1285]

How about using an undekink storage heater for kitchen use of hot water. Save on water wastage with the short run of pipes.

[@philsmith6165]

I do this now. 15 litre tank works a treat. Dishwasher and washing machine are cold fill, so little demand for hot water in the kichen.

[@UpsideDownFork]

We're not in the habit of using much hot water in the kitchen. We have cold fill appliances now and use the kettle when necessary for cooking. It's certainly a good solution for some. Thanks for commenting.

[@acelectricalsecurity]

Manufacturers are a little bit naughty really, because the vast majority of people will automatically assume that a 200L cylinder will give them 200L of usable hot water.

[@UpsideDownFork]

@@acelectricalsecurity exactly!

[@user-ry7yg2hk7i]

In my opinion the 300 l inverse/hygienic cylinder must have an electric resistance to supplement the heat pump or larger inverse/hygienic cylinder 500....800 liter. Heat geek super cylinder is GREAT but need also a larger heat pump and lost the efficiency on heat in this case. Cannot respect the rule of thumbs for undersize the power of heat pump for greatest SCOP.

[@UpsideDownFork]

I'm not a fan of immersion element heaters.

[@HowardBurgess]

I’ve never found out what the temperature of the 45 litres/person guidance is. It could be 45 litres of mixed bathing-temperature water (e.g. 38-40C). Or it could be 45 litres of the stored water in the tank. If it’s water in the tank, then what temperature is the guidance talking about? It could be 48C, but more likely to be 60C. Either of those would create more than 45 litres when blended with cold to a usable temperature. Does anyone know which the guidance is taking about?

[@UpsideDownFork]

I have searched for this several times and have not found a definitive answer. My interpretation is that it is referring to 45L of stored hot water at 55 degrees. So i've made a bad situation worse by turning down the store temperature of my already too small cylinder! If anyone knows better then please share!

[@SolAce-nw2hf]

Seeing this video I think you are being much too kind. This cylinder does not work for your family/home and the documentation does not leave much room for debate. Have them swap it out, pay for the price difference between the current cylinder and the required one. Maybe add some money for the time used or offer to pay list price for the new cylinder and sell the current one yourself. If it was my home I would be furious. Enough hot water is a basic requirement for any home, not a bonus feature.

[@UpsideDownFork]

I get your point. I think it's a bit of a first world problem. The sticking point really is around the fact that most installers don't make any promises of enough hot water from just one cycle per day. So in theory we have loads of hot water if we do multiple cycles. I get it, it's not the end of the world. I've had a couple of cold showers in the early days as I was figuring out settings but I'm one of those weird people that doesn't mind an invigorating cold shower from time to time! 😂

[@SolAce-nw2hf]

@@UpsideDownFork Okay, if you can get it to work for your family/home with two cycles and no discomfort, it may be something to leave as is. These DHW should last a very long time, so personally i would make sure the entire family is okay with this situation. And I still think they should have recommended a larger cylinder and should propose a good solution. This is pretty important to get right and it's not like you need to be a Heat Geek to figure out the correct size.

[@davecavaghan7889]

How hot is your water compared to a gas boiler?

[@UpsideDownFork]

I'm not sure what you mean? The hot water is as hot as I set it. Both gas boiler and heat pumps can be configured to produce hot water at higher or lower temperatures.

[@davecavaghan7889]

@@UpsideDownFork so could you set it to 60 like most gas boiler storage systems

[@UpsideDownFork]

@@davecavaghan7889 if you wanted to, yes. 60 degrees is scalding temperature though.

[@davecavaghan7889]

Can the heat pump achieve that on it's own or would you need an immersion heater

[@UpsideDownFork]

@@davecavaghan7889 the heat pump can heat the hot water to well over 60 degrees. There is a test somewhere that shows someone heating theirs to 73 degrees without the immersion.

[@pdath]

What country are you from?

[@UpsideDownFork]

The best one! 😉

[@pdath]

@UpsideDownFork Where in New Zealand do you live? :-)

[@UpsideDownFork]

@@pdath Well played! I hope to visit there someday!

[@offgridwanabe]

Even the most inefficient heat pump water heater is 50% better on your real efficiency, your wallet set the heat pump to supply your need of hot water and don't worry about efficiency just take the savings in $$ and enjoy a meal out.

[@UpsideDownFork]

Are you saying an integrated heat pump hot water cylinder achieves a COP of 5.4?

[@offgridwanabe]

@@UpsideDownFork No I am saying enjoy the financial savings and let the heat pump work. Trying to see how many angles can dance on the head of a pin will cost you more to get the last little bit than it is worth.

[@Harve6988]

So basically, tank sizes are a con. Also, how this is going to work on a society wide scale to replace combi boilers - God knows. Most terrace houses for example that have lofts converted are not going to have anywhere for a 200L tank.

[@UpsideDownFork]

That's one way to look at it. Smaller properties will have to have a solution like the heatgeek combo cylinder that is much smaller but replenished very quickly. It's definitely a challenge that needs more innovation.

[@ponchod2924]

You should have got a joule cyclone tall and slim

[@UpsideDownFork]

Hindsight is a wonderful thing!

[@DigitalPosion]

Did your installer promise a certain cop? I just don't see what grounds you would have to ask for any money back. Your system works albeit not as efficiently as it could if say it was done by another more competent installer. But unless you were guaranteed certain efficiency all installer is obliged to do is put in a working system which they did manage to do.

[@UpsideDownFork]

Yes, you make a good point and I agree to some extent. It's all about setting expectations and managing them I guess. My expectation may be too high in this case. It's interesting that this video has generated very different comments. Many telling me that I'm too easy going about it, yet yours is pointing the other direction. Anyway, I hope if nothing else this video just raises some awareness.

[@DigitalPosion]

@@UpsideDownFork it comes down to contractual law, everyone is different and another person less educated than you could have been over the moon with install. But as long as the installer fulfilled their contract they deserve full payment for it. This is why firms who then come out with a cop guarantee should have an advantage (or a selling point) over your average installer, because they can be held accountable.

[@UpsideDownFork]

@@DigitalPosion Yep, I opened the discussion with the installer to see what they thought about the sizing of the cylinder. To be honest I didn't revisit all of the paperwork to find out exactly where I stand. The installation team agreed with me that the cylinder was too small, as did the other department I was in contact with. They've pushed the blame onto the surveyor/design team. There's been much discussion between them internally. I haven't pushed the matter and have been quite open that we've been working around the issue just fine. If they had pushed back from the outset and stated their position and why they'd delivered as agreed then I would have sucked it up and moved on, no big deal.

[@ricardopelc-wesoly3483]

"If you fail to prepare, you prepare to fail", Do your homework!

[@UpsideDownFork]

@@ricardopelc-wesoly3483 a good motto to live by 👍

[@davebax6819]

Hi trying to get someone on a KZbin channel I watch to share their octopus referral code with me so I can add it to my new app account…lol

[@UpsideDownFork]

@@davebax6819 😂 always room for another link! 😁 share.octopus.energy/bold-mist-390