Non-motoring > How does a hot water tank work?	Miscellaneous
Thread Author: Bobby	Replies: 28

New Wed 21 Sep 22 11:43   How does a hot water tank work? - Bobby

A family discussion at the weekend about energy savings. Hot water tank linked to a system boiler. Assume water runs through the boiler and is heated up and then put in the boiler and stored. Water is then drained from the tank when you turn on the hot tap. But you can run the hot tap until you have used all the water and it runs cold so therefore the tank must backfill with cold water when the boiler isn’t on? Is that right? In which case does it always add cold water every time you run the hot tap and the boiler isn’t running? So when you run the boiler again does it take the water from the boiler, heat it up again and put back in boiler? Or does it just add more fresh hot water into tank? My sister says she only runs the boiler for 30 mins a day and that gives her all the hot water she needs for the day and I am trying to equate that with mine where I have a pressurised vented (or is it unvented) cylinder. I usually have my hot water on for 2 hours in morning and same in evening. Of all the DIY stuff I have picked up over the years, I have just never got my head round boiler and heating! Confused of Lanarkshire. Reply to this message | Report message

New Wed 21 Sep 22 11:54   How does a hot water tank work? - Zero

Your boiler runs hot water through a closed curly loop in your hot water tank. The loop transfers it's heat into the water in your tank. When you draw hot water from your hot tank ( via the top ) it's replaced by cold water in the bottom, so if you use too much hot in one go, you end up with cold, till the closed loop from your boiler can heat it again. Your boiler is just acting as a heating element. Unlike a combi boiler. Last edited by: Zero on Wed 21 Sep 22 at 11:56 Reply to this message | Report message

New Wed 21 Sep 22 12:00   How does a hot water tank work? - Bobby

Ah right. That makes sense. So everytime the hot water tap is opened it is effectively adding cold water into the tank. Missus has a habit of running the hot water taps to rinse things and the chances are she turns it off before the hot water had physically reached the tap but in that time it’s added more cold water to the tank! Reply to this message | Report message

New Wed 21 Sep 22 12:14   How does a hot water tank work? - Crankcase

FWIW, I too used to run the hot water for a long time each day. Then I tried reducing the hours to see how far I could go before there was insufficient hot water. I'm now down to 30 minutes in the morning, the least the Nest can do. The water is still hot as anything 23 hours later. Actually I measured the temperature of it recently - 55 degrees. It seems my boiler does 55 degree hot water with no controls to change it even if I wanted to. The manual seems to say the temperature gauge on the boiler only changes the central heating temperature. I'd like to think that's wrong somehow, because 55 is too hot in the taps really. I already altered the thermostat on the immersion cylinder itself (which can be electrically turned on at the wall if you needed to, but very firmly isn't), but that made no difference at all. Reply to this message | Report message

New Wed 21 Sep 22 12:40   How does a hot water tank work? - Bromptonaut

>> Actually I measured the temperature of it recently - 55 degrees. It seems my boiler >> does 55 degree hot water with no controls to change it even if I wanted >> to. The manual seems to say the temperature gauge on the boiler only changes the >> central heating temperature. Presumably you have a copper cylinder heated indirectly from the boiler as in Z's explanation to Bobby. We have that system too but there's a thermostat attached to the cylinder which will close the valve to the coil or, in HW only mode, shut off boiler and pump when the target temperature is reached. IIRC my daughter had a system like yours at her previous house - cylinder in airing cupboard but no thermostat. I did some training on energy advice shortly after joining CA as an employee and have a City and Guilds qualification. Never used it; he then manager needed accredited advisers to match numbers required for a funding bid. I'm sure we were told then that 50/55 was recommended for hot water systems as the Legionaries bug could thrive up to that level. Reply to this message | Report message

New Wed 21 Sep 22 12:49   How does a hot water tank work? - CGNorwich

Recommended temp for cylinder to stop Legionnaires disease is actually 60C. I believe system using lower temps like heat pumps actually use immersion heater to periodically raise temperature to that figure. Legionnaires is quite nasty so Iwouldn’t chance a lower temp. Last edited by: CGNorwich on Wed 21 Sep 22 at 12:49 Reply to this message | Report message

New Wed 21 Sep 22 12:20   How does a hot water tank work? - Bromptonaut

>> So everytime the hot water tap is opened it is effectively adding cold water into >> the tank. Missus has a habit of >> and the chances are she turns it off before the hot water had physically reached >> the tap but in that time it’s added more cold water to the tank! We've been reviewing our usage of hot water and realised we loose a lot because it's drawn out of the tank but never reaches the tap. As there's a diffuser on the tap it takes an age to run warm. Now trying to (a) use the cold tap for rinsing bowls etc before they go in the dishwasher and (b) run water to wash glasses and other odds that we won't put in the dishwasher only once a day. Have reduced the boiler from being on all day for hot water to just a couple of hours in the morning and again in the evening. May reduce that later as the new Smart Meter evidences actual burn time. As part of a wider economy drive we've emptied and isolated second fridge and freezer that were in the garage running less than half full, consolidating everything in the fridge/freezer in the kitchen. We'd stopped using freezer #2 after the kids moved out and my stopping commuting tp London changed our eating patterns/habits but re-instated it during the pandemic when were shopping less often. Reply to this message | Report message

New Wed 21 Sep 22 12:35   How does a hot water tank work? - CGNorwich

Hot water is a comparatively small element in overall costs so wouldn’t go overboard with little changes. It’s house heating in the winter where all the money goes Reply to this message | Report message

New Wed 21 Sep 22 12:37   How does a hot water tank work? - Bobby

We usually run 3 showers (from the tank not electric showers) and maybe 4 or 5 baths a week. Our tank is huge though. Floor mounted and must be about 5 foot height. Just checked - it’s unvented and 260 litres in size. Is that normal?? Reply to this message | Report message

New Wed 21 Sep 22 15:12   How does a hot water tank work? - Manatee

>>Just checked - it's unvented and 260 litres in size. Is that normal?? 260L. is fairly large. Ours is 300L but that's because we have a heat pump and have our HW at 50 degrees or less. That's for a nominally 5 bed house. As somebody mentioned it gets blasted up to 62 degrees once a fortnight by the immersion heater to kill off any legionella. Although I don't know how the legionella would get in to a pressurised system. Actually I think heating the cylinder is almost certainly a waste of energy as it is constantly replenished by fresh water. If we have any bacterial growth I imagine it will be in the pipework of the unused showers in the house. With that in mind I flush them through when I remember to do it. Does unvented mean pressurised system? If so then like us you won't have a dead pigeon tank in the loft, and your HW cylinder will be replenished from the main directly. They only seem to install pressurised systems now, new to me but it does mean we don't need shower pumps. Reply to this message | Report message

New Wed 21 Sep 22 12:54   How does a hot water tank work? - MD

I've tried for the last 44 years to explain this to mine. Waste of e-fin time. It's similar to 'thermostat'. Same problem. Treats is like a lever :-) Reply to this message | Report message

New Wed 21 Sep 22 13:11   How does a hot water tank work? - Rudedog

Same here.... often hear 'is the heating on?', 'Yes the boiler is set to be on', 'But the radiators are cold', 'that's because the thermostat has reached the set temperature'....... 'so the heating isn't on then?' Give up. Reply to this message | Report message

New Wed 21 Sep 22 14:07   How does a hot water tank work? - smokie

SWMBO used to insist we needed 90 minutes boiler on in the morning and another 60 minutes late afternoon to satisfy hot water requirements. I installed a solar diverter in the early summer to heat the immersion with free power and at times we have not had it on for days as a result, and even as it's getting cooler and less sunny 30 minutes of the boiler in the morning seems to provide enough most days. The solar thing adds very little now. Gas usage July & Aug 2019 645 2020 670 2021 102 But I realise that's only £35 or so. I can see that when the boiler is only on for an hour in the morning now it uses about 6kWh a day whereas before it was more like 13 over the 2.5 hours it was on. That is fairly comparable even with the solar device. Also I've mentioned before the massive saving by changing the old 1986 freezer for a new one. The new one uses about a third of what the old one did, at 0.68 kWh per day compared to 2.2. Reply to this message | Report message

New Wed 21 Sep 22 14:32   How does a hot water tank work? - Bobby

Sadly I cannot get a smart meter for my gas so unless I go out to the meter every day at the exact same time and take a reading then I don’t have an easy way to compare. Reply to this message | Report message

New Thu 22 Sep 22 16:06   How does a hot water tank work? - rocket again

''a solar diverter in the early summer to heat the immersion with free power '' Can you tell me what device you installed and cost please? I've been looking at the Marlec Solar iBoost Reply to this message | Report message

New Thu 22 Sep 22 16:25   How does a hot water tank work? - smokie

I got a Solar iBoost from www.heatershop.co.uk/search?query=iboost Seems to do the job well enough though I really don't have enough panels to benefit as much as I might. Easy enough to fit yourself really. I paid £330 but I see it's now £370!! That's quite some inflation over 4 months!! Reply to this message | Report message

New Thu 22 Sep 22 16:47   How does a hot water tank work? - Fullchat

I too was looking at the Solar iBoost and the Solic 200. Both the wireless models as its something of a run between the Meter box/Fuse box and the hot water tank for hard wiring. Have come into it very late in the year as its been a cracking year for solar and now energy prices are sky rocketing. There seems to be a shortage of the products with both stating possibly sometime in November. The Solic is reasonably priced and comes recommended. Reply to this message | Report message

New Sun 25 Sep 22 18:21   How does a hot water tank work? - rocket again

The Solic 200 looks a good choice, thanks for the tip Reply to this message | Report message

New Wed 21 Sep 22 15:25   Hot + cold fill washing machines - Manatee

Slightly apropos savings on water heating - I was quite taken with the idea of having an EBAC washer, promoted as British made and also with hot and cold fill. In theory this means using water you have already paid to heat, rather than letting the washer do it with direct electric. Sounds smart. However - it typically takes ages to get the water running hot. By which time your washer will have already taken in its required 15 litres or whatever, and will have to heat it anyway. In the end we got a Bosch cold fill only. After the plumbers had finished they told me I could have had a system in which the hot taps are all on a circuit in which hot water constantly runs so that when you use a tap or shower it runs hot almost immediately. Apparently this is what they put in hotels now. I must say though that the idea of keeping that 50 metres or whatever of pipe full of hot flowing water all the time doesn't appeal. Reply to this message | Report message

New Wed 21 Sep 22 15:51   Hot + cold fill washing machines - MD

It's called a secondary return. Reply to this message | Report message       1

New Wed 21 Sep 22 16:13   Hot + cold fill washing machines - martin aston

I am surprised at how long some of you run your hot water heating each day. We have electric showers, dishwasher and washing machine so only need hot water for hand washing and a weekly bath. I give the water cylinder system a one hour run before running said bath about 50 minutes in and that gives me enough for a very deep, long bath and three or four days sink water thereafter. As others have said, the water takes time to run hot to the basin so often we just wash hands in cold or tepid water and may not run the water heating again until another bath beckons. Having said that the cylinder is modern and well insulated so running for an hour or so each day probably wouldn't be too heavy on the consumption. It would probably cut out after a short time when the thermostat kicks in. Last edited by: martin aston on Wed 21 Sep 22 at 16:13 Reply to this message | Report message

New Wed 21 Sep 22 19:00   Hot + cold fill washing machines - CGNorwich

We have a gas boiler and a gas hob. Constantly available hot water and cooking currently cost on average 50p a day. Not really worth worrying too much about. In fact it’s a bit of a bargain. It’s the heating bill that costs the money. Reply to this message | Report message

New Thu 22 Sep 22 11:19   Hot + cold fill washing machines - Fursty Ferret

Mine is running for an hour a day at the moment and that covers ~4 showers. Once a week it gets a solid 4 hour block to kill off anything dodgy growing in the tank. Reply to this message | Report message

New Thu 22 Sep 22 11:58   Hot + cold fill washing machines - Manatee

>>I am surprised at how long some of you run your hot water heating each day. Ours is on 24/7. When I've got a baseline trend I'll think about messing with it; the supplier of the system said to just leave it on all the time and use the thermostats to control the heating. Until a few days ago I had all the room stats right down to ensure heating was effectively off. The heat pump has its own electric meter and with just hot water it has been using between 2 and 3 kWh per day which seems not too bad. HW is set at 50C and reheats when it drops to 42C. I put the stats in two bathrooms, a bedroom and lounge up to 22 a few days ago when the temperature dropped. It put the consumption up to about 7kWh daily. Without adjusting stats and with a rise in outside temp it has dropped back to 4kWh yesterday. I'll see what happens when we get in to some properly cold weather. Then I'll look into variable pricing if available and the possibility of running heating at low priced hours and not at the most expensive times. It's all underfloor, and particularly downstairs where we are heating about 100mm of screed it shouldn't really matter much just when the heat goes in. We finished the loft insulation yesterday - I noticed that the eaves over the coldest bathroom had no insulation on the ceiling which probably explains something! I can feel a few experiments coming on. At some point I will put all the air stats up to say 25, and then when its up to temperature turn them all off, and see where cools fastest. I can then add insulation above the upstairs rooms with the highest heat loss. Reply to this message | Report message

New Thu 22 Sep 22 12:11   Hot + cold fill washing machines - smokie

If you can borrow an FLIR camera it will show you the hotspots and more importantly the cold spots in your house. Best done when it's colder really. I borrowed one from Octopus a year or so back (through their forum), I think they are still loaning it but it's already fully booked. It attaches to your phone. Reply to this message | Report message

New Fri 23 Sep 22 09:30   Hot + cold fill washing machines - smokie

.. and just after I mention FLIR cameras along comes a decent offer on one www.amazon.co.uk/dp/B0728C7KNC?smid=A2OAJ7377F756P&tag=pepperugc03-21&ascsubtag=2399503948 30% off at £151. Maybe we should club together for one :-) Reply to this message | Report message

New Thu 22 Sep 22 12:11   Hot + cold fill washing machines - Fursty Ferret

>> not too bad. HW is set at 50C and reheats when it drops to 42C. >> Don't know what the plumbing in your hot water system is like but I'd be thinking about adjusting that temperature upwards. Legionella thrives in 40-50C temperatures. Reply to this message | Report message

New Thu 22 Sep 22 12:37   Hot + cold fill washing machines - CGNorwich

I think Manattee hasa heat pump and they operate at lower temperatures than gas boilers. Typically they use the immersion element to heat water in tank to over 60C periodically to kill any bacteria in tank Reply to this message | Report message

New Thu 22 Sep 22 14:43   Hot + cold fill washing machines - Manatee

>> I think Manattee hasa heat pump and they operate at lower temperatures than gas boilers. >> Typically they use the immersion element to heat water in tank to over 60C periodically >> to kill any bacteria in tank >> Correct. Although, as mentioned, I think the unused shower pipes etc. are more likely to breed bacteria. Reply to this message | Report message