Hot water tank, how long do you have your boiler on for?

[PhoneWaiting]

Old house had an on demand boiler which was great. New one has a hot water tank from a gas fired boiler, can’t work out how long to have it on for without risking a day or two of no hot water trying to turn it down.
how long do you have your boiler heating the hot water for/how many times per day and how many people?
Also should I time it for when it’s also on for the heating, is that more effacent if it’s firing anyway or should I have it on separately?

I’ve only ever set mine for 30 mins in the morning and 40 mins before dinner. It does us, family of 4 with everyone out most days. I’m at home a couple of days a week but that makes no difference, our shower is electric so it’s only for dishes and hand washing, if someone wants a bath it goes on for an extra 20 mins but that’s not very often.

I got this down to a fine art this summer with help of gas boiler engineer checking the minimum temperature was safe.

It's 12 minutes in the summer and 18 in the winter. Once a day.

I have a hot water tank next to a boiler.

We've moved to 45mins once a day which does 1 big bath and 1 shower. Might need to turn up the temp as it's not very hot and will probably need to be hotter in winter.

I am using nearly 4kw electricity for heating my unvented hw cylinder each morning. I have a heat pump.

This seems a lot. What is your usuage?

When you say "usage" I assume you mean energy.

So you don't mean 4kw but 4Kwh. This may sound picky, but if your heat pump is rated 4kw and runs for 30 mins to heat your water up then you are using 2Kwh rather than 4Kwh.

Water has a specific heat of 4200j/kg/degree C.

So let's say you have 100 litre tank and the cold water in it is at 15 degrees C then to heat it to 40 degrees C requires :

100 (1 litre=1 kilogram) x 4200 X 25 (40-15 is 25 degrees) = 10,500,000 joules

1 million joules is 3.2 Kwh, so divide by 3,200,000 to get the joules into Kwh

=10,500,000/3,200,000 = 3.28 Kwh

You can sub in your figures to calculate how much "free" electricity your heat pump provides, as in theory the amount you use in electricity for the pump should be less than the amount of energy you should theoretically require to heat your water up.

Bear in mind there are losses of heat in the pipes, plus the pump requires some energy to run as well.

Sorry I made a small mistake,

1 kwh = 3,200,000 joules, not 1,000,000 joules = 3.2 Kwh !

Thanks for all the replies, really useful. This week with only 2 in the house I’ve got it down to 30mins a day with 2 showers and general hand washing might have to increase back up.

genuine stupid question! When you use hot water, does the tank drain down to empty until the boiler kicks in again and refill it? Or does it stay full and get topped up with cold water as it empties? And I’m guessing there’s no way to tell how much water you use on a shower or is left? On demand was so much simpler!

@jazzandh thats something I hadn’t though about with legionellae. I admit I don’t know what temp my boiler heater the water too!

also I guess I should be running the bath we don’t use as well? Or if water is flowing say to the toilet next to it regularly, is that enough movement for it not to come out the bath tap or coils it wash back and infect the whole system?

my brain is thinking too much!

20 mins a day. If we were to do an hour I can skip the next day.

But that's with an electric shower and dishwasher so just for hand washing and kids baths.

30 mins for 2 showers and evening face washing

30 minutes morning and evening. Family of 5.

We've just stopped ours coming on in the afternoon and haven't noticed any difference. The water tank is really big as the plumber though six of us would be running baths every evening but we only have showers. It comes on for an hour and a half in the morning.

Combi boiler that heats the water as we need it

GasPanic. My energy use is 4kwh for the hour of hearing. My energy supplier's graph tells me

This is a bit off topic but we have just installed an Eddie.

It's a little bit of kit that diverts (mops up) excess solar panel production and directs it to the immersion heater.

So our water is hot on bright days with no charge to heat it.

Only works with solar panels though.

240L unvented tank from a 30KW system boiler next to each other.

summer was 10 mins in the morning 10 mins at night.

now and winter will be 20 mins morning 30 mins at night.

We had electric showers, or ran just a shallow bath for ds when young and 45mins once a day was enough..

Reduced recently to 30 mins in morning and 30 mins in evening. Occasionally boost for 15 mins if DD has one of her epic showers and someone needs shower straight after. Haven't run out of hot water and have reduced gas usage

Oil heating boiler

20 minutes in morning once a day and water is always roasting and plenty for family of four to shower etc.

Should of said we used to do twice a day and I and stopped and still plenty of hot water

I think you might be surprised how little you need it on

I would try 20 minutes once a day and I think you will find it's enough.

3 adults at home, and an hour in the morning provides enough hot water to last the day.

It obviously depends on the size of your tank as well as the amount of time you have it on but ours is one hour in the morning for four adults (two real ones and two older enormous teens) and it’s plenty for three showers one bath and kitchen use. I’m sure we could probably reduce the time a bit.

We've recently had this where we moved. We've found 2 hours morning, and 2 hours evening is plenty for us. Constantly have hot water. I was told its more economical to keep it constantly warm than to let it cool too much and need to reheat in terms of energy. So far so good as lived here a month and used barely any gas.

I was told its more economical to keep it constantly warm than to let it cool too much and need to reheat in terms of energy. So far so good as lived here a month and used barely any gas.

This isn’t correct. I’d try an hour in the morning and an hour in the evening. Even that will probably turn out to be too much

2 adults and 2 kids aged 2 and 6.

On for 45 mins on weekdays mornings.
for 1 hour 15 mins on weekends mornings.

never on in the evenings.