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Stretching your budget? Share tips and advice to discuss budgeting and energy saving here. For the latest deals and discounts, sign up for Mumsnet Moneysaver emails.

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Original poster

Please help clueless me understand if i’m wasting money on heating water

67 replies

Brokenbuttercup · 31/08/2022 18:03

Sorry if this is a stupid question but I’m a but clueless when it comes to house stuff (stbxh always sorted such things and I really don’t want to ask him!)

I have a system boiler with a gas boiler in the kitchen, a large water tank in the airing cupboard and a digital thermostat in the hall. It’s a new build house, and as such it’s pretty warm and doesn’t need a lot of heating. I’ve set the thermostat to standby meaning the central heating is essentially off but will guard against frost damage. Hoping to keep this off until we get to the real depths of winter.

The bit I’m struggling to understand is the hot water. My boiler is permanently on and I therefore always have a full tank of hot water. The tank is massive and I really don’t need that volume of hot water. Should I be setting a timer for my hot water? Is it constantly using gas to keep the tank full and heated or does it just top up hot water once I have used some? I’m not sure if not using any of the water to heat the radiators actually makes any difference to the amount of gas I use if it’s in the tank already and constantly being heated??

I have tried Google but it’s hurting my head. Can anyway explain how it works in layman’s terms please??

OP posts:

Soontobe60 · 31/08/2022 19:06

Brokenbuttercup · 31/08/2022 18:26

@Nolongera good question. Will have to take a deep breath and have a hunt around in the cupboard of crap, aka my filing system

If yo google the name on your boiler / water tank you may well get an instruction book / user manual or YouTube video showing how it works.

TheCatWithGreenEyes · 31/08/2022 19:08

We have this type of boiler. We have always had it on for 2 hours a day and this has given us enough water for our large family of 7. At least 7 showers a day and washing up morning and evening. We went away for 4 nights recently and turn it off but when we came home we had enough scalding hot water for all of us to shower. I’ve just this week reduced it to an hour a day to see how I get on so far so good.
I worked out 2 hours a day on my fixed rate so over the price cap as bit cost around 1.70 a day so hoping to get it under this.

iknowimcoming · 31/08/2022 19:10

The heating and hot water are separate so the hot water in the tank comes out of the taps and doesn't go to the radiators. And the hot water in the tank doesn't go cold (and need constant reheating) it just gets cooler when you use the hot water and the tank automatically tops up with cold water if that makes sense? So it's best to have the hot water (heating) on before your peak usage. Try an hour in the morning and evening before showers/baths washing up after dinner and see how you go, if you never notice it running out reduce the time and if you run out frequently increase it

JS87 · 31/08/2022 19:13

i thought all new builds had to be fitted with condensing combi boilers?

LadyGardenersQuestionTime · 31/08/2022 19:14

Just two of us in the house and I managed to get ours down to 3 x 20mins a day, but that wasn’t quite enough. I;m experimenting with 1 hr in the morning and 2 x 20 min topups at the moment, but it’s all a bit of a mystery.

humdedum · 31/08/2022 19:15

mumda · 31/08/2022 19:03

Reduce time until it's not enough.

Yep this!
I put mine on for an hour every evening and that allows for 2 showers in the morning and enough hand washing hot water, throughout the day. (Washing of hands not hand washing clothes 😂).

You could probably fine tune it even further - Keep us posted.

etulosba · 31/08/2022 19:16

The whole tank doesn’t cool down to a constant temperature. As you draw hot water off, the very hot water rises to the top of the tank and the cold water that replaces it stays at the bottom. If you only heat the tank for a couple of hours a day you may only have very hot water in the top fifth of the tank, but that may be sufficient for your needs on an average day.

Hugasauras · 31/08/2022 19:19

JS87 · 31/08/2022 19:13

i thought all new builds had to be fitted with condensing combi boilers?

Condensing, not combi.

Hugasauras · 31/08/2022 19:20

System boilers and tank give better pressure so you generally see them in new builds with multiple bathrooms.

Of course from 2025 no new gas boilers!

Nidan2Sandan · 31/08/2022 19:23

Ours is on for 1hr in the morning and 1hrs at 4PM and we havent run out of hot water yet. We usually get 3 or 4 showers out of it plus any extra.

We do have the showers fairly cool at the moment though, so wonder what it'll manage in winter when we turn them up a bit.

filka · 31/08/2022 19:26

It's not a stupid question at all, the answer can be quite complicated. This may help a bit (and on some other myths and truths):
www.cse.org.uk/advice/advice-and-support/energy-mythbuster#:~:text=It's%20better%20to%20leave%20the,is%20stored%20in%20a%20tank.

Personally I've always left the hot water on 24/7 on the basis that keeping it hot all the time is more efficient than letting it cool, then heating it up again. In principle the thermostat stops the boiler running when it isn't needed, and you'll never run out of hot water. But I'm having some doubts about that theory at the moment!

Essentially, you only want to heat the water that you use. The boiler has a fixed heat output, so the longer you have it on, the more hot water you get. So one option as noted above is to progressively reduce the heating time until you find that you run out of hot water, then just increase the time a bit until you don't run out. God help you if one day you want a bath instead of a shower.

But as the link confirms, washing machines and dishwashers heat their own water and use less water than if you tried to wash clothes and dishes by hand

Original poster

Brokenbuttercup · 31/08/2022 19:26

@iknowimcoming @etulosba thank you! That’s just the kind of explanation I needed

@JS87 its because the house has multiple bathrooms (2 baths & 2 showers) so they usually recommend system boilers in that set up (according to Google!!)

OP posts:

JulieMarooley · 31/08/2022 19:26

I read the temperature needs to be kept high to kill bacteria, but it seems such a waste to heat it to 62 degrees if you then dilute it to 40 to have a shower. In our case we dilute with cold water from a tank, which presumably is going to be full of bacteria anyway. Any wise thoughts on this?

etulosba · 31/08/2022 19:34

In our case we dilute with cold water from a tank, which presumably is going to be full of bacteria anyway. Any wise thoughts on this?

The cold, bacteria ridden water from the tank in the loft that probably has the remains of a rooting squirrel in it enters at the bottom of the tank. By the time it gets to the top of the tank is is hot enough to kill the bugs. The water water to taps/shower/baths exits the tank from the top.

etulosba · 31/08/2022 19:34

Rotting squirrel!

etulosba · 31/08/2022 19:37

In our case we dilute with cold water from a tank, which presumably is going to be full of bacteria anyway. Any wise thoughts on this?

Just read that again and realised what you meant. You need to take your chances with the squirrel. Sorry!

Keep your mouth shut when you shower.

Hadalifeonce · 31/08/2022 19:39

We. Have ours on for about an hour in the morning and 30 mins in the evening, we can usually all manage a shower in the morning, with plenty for washing up in the evening.

caramelsauce · 31/08/2022 20:22

I have the same set up and have recently changed it to having it on for 30mins in the morning. This is enough for 2/3 showers a day for us and we haven’t ran out by evening when DH sometimes had a second shower.

iknowimcoming · 31/08/2022 21:20

Oh one more thing! In case anyone didn't know (I once had a tenant who didn't) if the hot water heating timings overlap with the radiator heating timings the boiler will prioritise the hot water over the heating so you need to ideally have them one after the other (for example hot water 5-6am, heating 7-9am etc)

gizmo · 31/08/2022 21:34

My gut reaction is that you're going to be able to get away with heating sporadically as water tanks retain heat for a long time (and should be lagged). But as @filka says if your system is operating correctly a heating control should turn off the boiler if no more energy was needed to heat water.

The question 'does it take more energy to heat the house continuously or to reheat it from cold' doesn't actually have a right answer that applies to all homes. It will depend upon how quickly your home loses heat, what it is built from, what the heating patterns are and whether it is getting heat from other sources (eg solar gain).

As a very rough rule of thumb a home which has a lot of heavy construction materials will tend to store heat and smooth out temperature fluctuations inside (especially so if well insulated). So when you turn the heating off you'll have a longer 'glide path' as things cool down.

Homes which are made of lighter materials won't need so much energy to heat the structure so when you turn the heating on you'll feel comfortable faster, but (unless they are well insulated) as soon as you turn the heating off you'll be back to square one.

catwomando · 31/08/2022 21:48

I had a boiler service and asked the plumber this question

He said

if you only use water at certain times eg a bit in the morning and then some more in the evening it's better to have it on timer
if you are at home and use the hot water more sporadically throughout the day it's better to keep it on constant.

Hope this helps.

JulieMarooley · 31/08/2022 23:45

etulosba · 31/08/2022 19:37

In our case we dilute with cold water from a tank, which presumably is going to be full of bacteria anyway. Any wise thoughts on this?

Just read that again and realised what you meant. You need to take your chances with the squirrel. Sorry!

Keep your mouth shut when you shower.

Yikes 🫣

Yellowblanketofdoom · 31/08/2022 23:52

Watching witn interest. We have a similar set up and all of the houses in our street have the same (all built by same company in last five years). I leave my water on all of the time. My neighbour turns his off and puts it back on after a few days. He swears it saves him money, but his usage is only marginally less than ours. We are a family of four and i WFH while there are only two of them in their house they're out most of the day. Based on how often just eat visit, I also don't think they cook very often either!

ScarlettSunset · 01/09/2022 09:22

My hot water is on a timer. It's on for an hour in the morning and a couple of hours in the evening. I have experimenting with how long I need to put it on for, but that seems to be what works best for me

lightand · 01/09/2022 09:26

will print out and keep this thread

I had all these questions a few months ago, and didnt know all the answers.

DH has now fitted a timer.
We have a weird system anyway in wintertime.
It is summertime when we can save some money

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