Hot water heating

[notingthewear]

We have a gas condenser boiler and a Megaflow hot water tank - currently the water is more or less left on all the time. And we haven't really given it much thought. I've tried googling on whether this is a good idea or not but the answers get muddled with immersion heaters and economy 7.

Anyone know about this stuff?

How much hot water do you need? We have a combi boiler, but when we had a hot water tank, we used to heat water for half an hour or an hour before we got up, and then for longer in the evening for baths, showers, washing up etc.

It depended on when showers and baths were being taken. We all have showers in the evenings now - we don't really use a lot of hot water during the day.

I'd like to know this too, having moved into a house with a tank. Always had combi boilers in the past. I'm just sticking it on for half an hour in the afternoon for our evening showers. But I don't know whether, once the heating is regularly on, that affects the water tank. So following for tank efficiency tips!

Used to be 4 of us - but the kids (and their 30 min showers) have gone to Uni - dh and I shower for 4 mins tops each morning. The dishwasher and the washing machine are cold water feed. There's such little info out there.

I put mine on for 1 hour a day, I tried 30 mins but it was running out. Just 2 of us.

It doesn't really sound as if you need to be a tankful of hot water on standby!

No it really doesn't but does the hot water and cold water not mix to become luke warm water?

Also following as I didn’t realise until last week that we have had the electric immersion heater on all the time - hate to think how much that has cost us.

now have gas boiler heating the 250L tank for an hour a day, not seeming to run run so will reduce by 15 mins and see if any impact.

And to further add to the challenge we can’t figure out how to change the timer - we always used the thermostat before. It’s a bit embarrassing that we don’t know how to work the basics

My hot water is on for 1 hour per day. My shower is electric and appliances are cold fill

@notingthewear

Your system is like mine. The megaflow cylinder is just a pressurised cylinder that helps with the hot water flow. The tank is probably very well insulated. Your boiler is a system boiler.

In order to minimise the energy, you should fill the hot water tank, turn the hot water heating off, then use the hot water in the tank. The turn off is normally done automatically by the thermostat when the water in the cylinder reaches temperature.

Example :

Say you have to do 2x showers and 1x washing up a day. You should heat up a full tank before you have the showers. Then switch the hot water heater off. Then have the 2x showers and do the washing up. This will use up the hot water in the tank, but will not replace it. The tank will then remain cold until you need hot water again. This saves the most money.

If you leave the hot water on all the time, what will happen is as you use the hot water up in the 2x showers and washing up, the boiler will fire up again and after you have used the water you need, the hot water in the tank will be replaced and the tank will still be full of hot water. The water will lose temperature over time, during the day the boiler will turn on again repeatedly keeping the water at the hot water temperature. So you will be keeping a tank of water at the hot temperature all day and night, which is wasteful.

Think of it a bit like either boiling a kettle once and then it switching off and you making your tea (efficient) or keeping the kettle boiling all day and you just getting the tea on one occassion (inefficient!)

How long will you have to leave the heating on to create 1 tank of hot water ? My tank is 145 litres and takes maybe 20 mins with a 24 kwh boiler. I would be surprised if your system takes more than 45 mins to heat up a full tank.

Bear in mind once you heat a full tank, it will probably stay hot for a day or so. So if for example you heat in the morning, then have 2x showers, then wait until evening to do the washing up, there may well be enough water left from the morning heating cycle that you don't need to switch on the hot water heating again - you just have to experiment.

As a starting point I would just put it on for once a day for 45 minutes about 45 mins before you need the majority of the water (normally for showers in the morning) and see where that takes you.

If you need hot water at night, or a single tank of hot water is not enough to cope with how much you need in the morning then further messing around is required.

Ouch.

@GasPanic great explanation, thank you. Currently got hot water on fo 45 mins in evening before showers, seems ok.

We finally pulled the instructions for the timer off the internet and the water has been turned on for mornings only. We’ll see how goes and tweak it if needed. Thanks everyone.

We are similar, 2 of us here with children left/at uni. We used to have it on for 2 hours morning & evening when everyone was here. Now we have it on for an hour in the morning & it seems to be plenty. 2 showers plus washing hands/washing up is all it is used for. Very occasionally (once since the summer) I will have a bath, & there was enough for that too.

@notingthewear

One thing you may find with your set up is that you can skip every second day in heating. You can do this if a) your tank is well insulated (the megaflows normally are) and b) the amount of water you use per shower is relatively small compared with the tank size. I think with a 250 litre tank having two 5 min showers a day you will probably be able to do this, especially if you don't use the water for anything else like washing up.

I found in the summer I could actually go for 3 days, but the water was a bit cold by day 3. OK in the summer when you don't want a hot shower but not good for the winter.

There is also the pain that the timers don't allow you to skip every second day well because there are 7 days in a week. Mine is set to come on mon, wed,fri and sun. The consecutive days on sun/mon give me a bit more water for the weekend and washing up.

Oh - and probably more to the point, skipping every day really will start to save you some gas. I don't know how much because I didn't meter it, but I would guess around 20-30%.

Thanks @GasPanic we are going to try 1 hr a day, that should give dh a warm shower before he leaves for work - I wfh so I can deal with the potential of a cold shower while we make adjustments. Will consider doing the every other day thing as well.
I’m thinking water temp dropping over winter might mean we’ll have to tweak things again.

One more thing I would say is that turning down the length of heating from say 2 hours to 1 hour will not necessarily save you gas.

The reason is that the water heating is an either or scenario. Either the tank reaches the set temperature (eg 65 degrees) or the heating time runs out. So if say you put the heating on for 1 hour, the boiler may only take 30 mins to get it up to 65 degree temperature and then it switches off. So in this scenario changing the heating time from 1 hour to 45 mins will have zero effect on the gas used.

If you set the water heating time to heat the water at the same time as you are using it from the tank, it becomes a lot more complicated because then the boiler will switch back on to make more hot water as you use up the water.

For me, you should only really have the heating switched on at the same time as you use it if the tank does not hold enough water for your needs, which may be the case if you are in a large house with lots of people using the shower simultaneously. Otherwise it's best to heat up the water only before you need it, then use it. If you don't do this, then you risk ending your use/showering period with a full tank of hot water which is no use to you !

This is hard to describe. Sorry.

thank you @GasPanic understood!

Understood @gaspanic!
I am going to see how we get on with 45mins and then try 1hr every other day.

My water is on a timer, one hour 4-5 pm. ThE hot water tank then is enough for me to have a bath in the evening ( shower is electric so doesn’t use the water from the tank) and any hot water needed the rest of the 24 hours for hand washing, rinsing cups, wiping down stuff etc

We have our gas water heater on for half an hour a day. We never seem to run out and it's costing around 60p a day incl standing charge.