Hot Water Settings Energy Suppliers Don't Want You to Know! 

I’ve managed to find my neighbours electrical cables in the ceiling so have got my 3kw immersion running for free. I call that 100% efficiency

This one is a no brainer but most engineers don't educate clients enough. Cheers for the helpful video

Thanks Adam, well presented and informative as always.

I'm in Australia in a 12 unit block. We're hopefully installing a new central hot water (COP of up to 6.0) twin heat pump and 400l tank system. We are required to have legionnaires disease protection. The Reclaim energy branded heat pumps are made by Panasonic in Japan. There's a smart controller that varies the storage tank temperature in 5 modes. Output temperature is 63 degrees C. The tank is heated to this temperature once a day. A 55C thermovalve is used with a timed recirculating pump. The cost of replacing the 315l tank and gas instantaneous heater up to current codes is $AU33k. The total heat pump cost is $AU16k less $AU6.3k government subsidy.

Thank you I'm going to try everything you suggest and see what difference it makes. But I have noted down all the changes just in case.

I followed your advice 6 months ago ago and put my cylindre at 50c with the boiler heating the water when it reaches 45 (evohome). I don’t see any difference as a user but I see that I can run my flow temperature at a lower temp with lower gas bills. 👍 thanks again.

45°C is exactly the temperature I have set for hot water 💚💚

Quality video as always !

I set my water heating heating time to 12 midday to increase efficiency due to warmer outdoor temperatures (compared with 2am as set by the installer) at the same time as I’m typically cooking so don’t need any heating downstairs in the open plan area 👍

Brilliant video, thank you!

In an ideal world, yes, keeping the water temp just right so that the showers get water at your preferred shower temp, but what about houses that don't have massive space for the cylinder. I see lots of vids where they seem to be in garages or cellars with spaced-out pretty piping and that all looks very nice and the cylinders are colossal. But back in the real world where most people live in tiny houses with no space and three kids, where the wife takes a 20min shower and then three teenagers and a dad use 5-7mins each, well we need about 300l of water despite having room for a 200l tank, in that circumstance I'm afraid you need to heat the water to 50% higher temp and down-mix it, e.g. 56 degrees mixed down to 38 at the shower. I don't want to poo poo this advice, which is usually excellent and incredibly well thought-out on this channel with great physics to back it up, but on this occasion I think a caveat to acknowledge that, excepting baby boomers, no one can afford the sorts of houses our parents had and are living in seriously space-poor buildings with room for not-so-massive tanks. I just saying, that I reckon at least 60% of the installs will be in houses that cannot possibly put gigantic tanks in that would allow for 5 showers every morning within an hour of each other if the water is only heated to shower temperature. By the way, one small note on the eco-mode to drop the heat output during the hot water cycle - I found during a lot of playing around this winter, that it actually used MORE energy (although only slightly) and I think its because it was taking so long, that the outside air temp had dropped out of its maximum and it seemed better to leave it on the more powerful mode to get it done quickly during the hottest hour from about 14:15 (not 14:00 in my location, that could be due to hill side, I suspect it varies a bit), to 15:30. Also I have to say that the outside temp and the time it stayed hottest varied so much from day to day (literally 10 degrees from one day to the next on occasion) that my tests were likely not statistically terribly good. Edit, oh, also note that I have an ecodan, not a viesmann which might have far more sophisticated eco-modes, although I did watch the flow temps and it certainly does change it, dropping it and chasing about 7 degrees above the current tank temp until about 40 where it always flatlines to the target temp, I guess more snazzy kit might do something more cunning.

well, i am doing something similar in an off grid rental with solar. generaly keeping the tank at 45c, but when there is excess solar, starts heating up to the maximum allowed of around 75c. I am also starting to incorporate a bit more smarts to it through home assistant, with information about its temperature and solar forecasts.

Managed to implement viesmann style control on my vaillant this morning!

I have a Daikin, my hot water store is already set to eco 48, it is on a schedule with a reheat setpoint of 39, I have just enabled another schedule for ultra quiet mode at the same time as the hot water call, hysterisis is set to 2c, is there anything else I could set?

The amount of arguments I've had with my colleagues about doing this. In the end in an electric only block I set up some flats this way while other flats were left at the standard set up, the difference was almost £100 a month and no complaints as they're required to have temperature limiters at outlets in new builds. They're heated by Heatrae Sadia Amptec units so the saving is no where near would it could be with a heat pump, sadly these flats aren't suitable for heat pumps in the future due to the short sighted design of the new builds being built. Then for 2 hours a week the immersion heats the tank to 65c for disinfection. This only works because the Amptec units can just about keep up with the hot water draw off though - one bathroom. If there are 2 bathrooms the storage temperature needs to be higher.

Great Video as all ways. A little clarification or help please. At work we have a 300L vented DHW cylinder, and 2 gas boilers. This supplies an 18 bedroom Care home, with 12 bathrooms and 16 residents. Did you say in the video that in fact storing the water 70 degrees would probably be the most efficient policy as it would 'double' the overall hot water volume? ie at the point of use, cold water mix ratio would mean we use less hot water as distributed at 43 degrees to the tap/shower?

Excellent video again! Personally I have an iboost fitted and supplies my hot water pretty much from May to September and the heat pump does the rest outside of this

Looking to install heat pump. Now that Mixergy has Heat Geek setting how does this compare to Newark HG range?

2 - 4pm is also our peak solar energy production time so we are storing excess electricity as hot water. Only had the system since last week but we seem to be importing no more electricity than we did before the installation plus we are not using gas for hot water and not paying the standing charge.

Does anyone know if it is possible to adjust the temperature differential on a NIBE heat pump during hot water production? During the summer, it seems inefficient to me that the hot water cycle is only 45-60 min when the heat pump does not have to provide space heating (or cooling).

Very informative! Curious about what equipment you use to shoot/light your setup? I talk movies and am making an equipment list. My room size/shape is similar to this one.

Are you able to share more on how you are using the flow meter to set the temperature. Are you doing this manually or have you automated it? Ideal if manufacturers integrated this but in the meantime it would be good if someone put together this logic on Home Assistant. I can control my Ecodan from HA so if I had a flow meter connected maybe I could implement this level of control.

Wow, lots of info here, will need to watch again. Couple of potential clarifications - RE HW store temp, can be useful to have it higher than usage temp if the capacity is not enough to satisfy demand. RE best heat time. While most efficient for heating may be 2pm, if it isn't going to be used until the following morning then there is a long time to lose heat. So may not be most efficient overall.

Are Viessmann heatpumps worth the extra cost? What makes them so different?

If you have a heat pump and solar PV and use cheap overnight electricity you can save more by lowering your hot water set temperature during the day so the heat pump only heats at night to the higher temperature when electricity is cheap. Also, never heat your water with "free" solar PV excess as that will just stop your heat pump heating the already hot water - the heat pump is much more efficient than the immersion heater and you are better off exporting the excess solar at today's export rates and importing at the cheap rate for the efficient heat pump. If you heat at a COP of three and import at half the export rate that's six times more efficient than diverting the solar to heat the water directly.

Respectful question/observation. Heating the water in the afternoon when the outside temperature is higher makes sense and will promote greater efficiency. However the cost of the electricity may be significantly higher at 2 in the afternoon than at 2 in the morning ? The actual heat pump/cylinder efficiency will suffer but the actual cost of heating the cylinder could be considerably less ? Thank you. Excellent presentation as always.

What about shower thermostatic mixing valves needing hot water 10C above mixed outlet temp setting?

I'm having a real problem with my Daikin controls for my hot water cylinder. Its an absolute disaster. I know how to control it but it wont let me control it efficiently. Any ideas on what to do?

I recently installed smart shower valves that have an energy harvesting function to light up the dial when the water reaches my required temperature. Sadly this system needs an hot water temperature of 55C! Poor design. We have a Daikin 8Kw heat pump with a 210lt tank to serve 3 bathrooms. We only have our first bathroom ready so far and are very dissapointed with the functionality. We are finding that the system can't deliver showers for 2 people without going cooler so we have to go to the home display to check before we take a second shower. We have Solar and battery so I would be happy to use lower cost or free solar energy to get the heat pump to take the water up to 55C. Also our Daikin system sucks a bit on water temperature as when we set a schedule and ask it to maintain a temperature it fails to do so.

We’ve done a few installs where the showers won’t mix properly unless they’re fed with 55 degrees + hot water. Something to think about.

My DHW is set to a 1 hour window at midday, to maximise use of excess PV. Certainly from April to September, my DHW is free :)

Currently have the boiler range rated to match the coil output (17kW), and 20oC differential. What's the best balance for rapid recharge and efficiency?

The reality here is that most people have oil fired heating on day timers. Yesterday I was sitting outside in the garden because it was 19*C! In an hour I heard 2 different neighbours heating fire up. Around noon! Most likely on timer from winter still. Most likely just stay there all summer too. You are picking at the 10% gains when most people are on oil and gas fired boilers with dumb day or week timers and a single thermostat in the coldest room in the house (downstairs hallway).

Thought part of the high temp was to deal with bugs in the hot water system. Not the case?

Is there a reason we don't just use thermal stores where the cold water feed passes through a coil in the tank to collect heat before heading to the taps? From my understanding, this would make leigonella a non-issue as the water in the tank never leaves the tank. Although, I guess the water in the tank would then need to always be hotter in order to create enough of a differential to get the tap water up to 45c before the end of the coil. Perhaps that is the reason?

if air source heat pumps extract heat from the air can they not be installed indoors and take advantage of the warmer air.

Did I understand you correctly that you’re using a temperature offset value of 0. If so, doesnt the HW take a very long time to get to temperature?

Haha energy supplier. You thought you could keep this a secret but now I know! Muuhahaha.

Reduced heat loss also helps in a heatwave and an overheated house.

maybe the ASHP needs a winter setting for DHW where it limits DHW to one hour and then back to heating for one hour and rinse and repeat until water reaches set point.

Don't forget that you also see reduced scaling at lower temperatures, increasing the life of the cylinder.

I use home assistent to use my "free" solar power into my house.

I see this channel is very heavy on Vaillant heat pumps. Is it simply the most optimal option available to them or they are sponsored by Vaillant?

Any gas boilers run an occasional legionella cycle on the hot water cylinder. Why can't heat pumps do that also. Are cylinder thermostats not sufficient? If water heating is on a schedule then no excess hot water should be there or at excess temp. Only ultra advanced cylinders can retain a lot of heat which few have.

Why can't a heat pump work on a standard open vented indirect cylinder therefore avoiding all the associated extra cost of unvented hw

So now you're interested in "magic widget" to plate load cylinders eh? ;-) Edit - Warning Marko should RTFM more often. See the excellent Mixergy reply below for further detail but in short the bit between the --- and --- doesn't apply. :-) Hot water tanks, once used, will have a layer of say 45C water on top of a layer of say 20C water. The exact heights of these vary depending on how empty the cylinder is. In a "conventional" cylinder with the boil in the base; gently heating this with a heat pump will bring the "20C" layer up to 40C before it starts to destrat and mix with that 45C layer. You then stir up the whole tank to 50C, 55C, or more if you particularly need extra stored water at the expense of COP. There is ALWAYS a layer of 45C water at the top though. --- The mixergy setup is designed for plug-flow heating OR fully stirred vessel. The moment that you kick off your "fully stirred" heating you're going to blend the tank down to a uniform "meh" of 25C then slowly heat the whole thing up to 45C again. In the meantime you've lost that "hot top" and so whilst the reheat process might be efficient the usability of the setup is poor. To fix this I'd suggest you need dual upper inlets and a baffle 1/2 to 2/3rds of the way up the cylinder. First take water from the base, through your plate, then inject under the baffle to "fully stir" the cold part of the cylinder. Only once that is near to the temperature of the "hot top" do you flip to stirring the whole cylinder. Design the baffle carefully and you might find that any cool water above the baffle will naturally mix itself into the lower part as you're heating it; thus maintaining the "hot top" and avoiding any need for dual inlets and switchover. It screws up the original mixergy "plug flow heating" and "heat what you need" USP but will work better with heat pumps. --- We had a similar requirement with a district heat system that needed to be >50C "hot top" at all times but also wanted to be heated by a heat pump as efficiently as possible. Stirring the bottom of the buffer tank through the heat pump at a rate of knots and allowing the warmer water to float up / cooler water to float down maintained the "hot top" whilst also retaining the "fully stirred heating" benefits for the heat pump. What are your thoughts on the continental approach of heating a primary storage (pipe the heat pump directly into the tank) then drawing hot water off that on demand via plate HX?

How do I find out how much hot water I'm using without the expense of fitting a water meter to the cylinder (which presumably would cost more than any savings)? We're a youngish family of four, but all told we probably take about 8 showers (pretty short with water off while we soap up) over a week and wash at the sink the rest of the time so I'm thinking that we'll be lucky to use much more than 100l of our 250l tank (40%) a day? Presumably there's no chance of me turning the temperature down below 65 on our unvented system boiler to allow for 53 degrees plus to cater for such a low turnover?

I'm sorry but 50deg C is too low for me, I have a heat pump set to 50deg C and I am having to boil my kettle to add to washing up water.

Why aren't you installing lambda heatpumps, the most efficient in the world based on studies of german universities ? Lambda is an austrian manufacturer which are also known under the german brand ZEWOTHERM who are building these under lambda licence. I have no lambda, but I checked that website with all the heatpumps that are being monitored and I wondered why non of the continental bests are installed in the UK like Lambda or Ovum.

Don’t tell me that I have just bought your new cylinder !

The basic reason heat pumps are wrong for hot water is that most households do not need that quantity of hot water as 80% of people use a shower to conserve water. I install bathrooms and more and more people do not want a bath installed. Heat pumps should be used for heating the house only

boiler/cylinder manufacturers are so lazy with their designs

Practice on those excessive hand gestures