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How long does a gas water heater need to be on each day?

(13 Posts)
BabCNesbitt Thu 25-Jun-15 13:20:23

We're in a rental, a draughty old Victorian terrace, and our gas bill was horrific over the winter. OK, not great, but perhaps (I thought) to be expected - next year, everyone in onesies from October onwards. But I've just done a meter reading and checked online and our bill for the last three months is still £250 for the quarter.

So I checked the times our water heater is on, and it's been on every day from about 6am until 10pm. I know, I should have checked earlier, and this seems excessive. But could this explain the £££ bills? And if so, how long do I need to be running it each day? We have an electric shower, wash dishes by hand once a day, and DD has a bath every other night. Other than that, it's just normal hand washing during the day (I'm a SAHM). How long should the boiler be heating water during the day on that basis?

specialsubject Thu 25-Jun-15 13:43:42

the electric shower heats its own water.

to calculate how long the boiler needs to be on, you need to know:

the capacity of the heater in kw
the volume of the water
the start and end temperatures.

it is then a simple physics calculation.

more simply...we have a standard airing cupboard hot water tank (oil heating). The hot water is on for an hour a day. That does a bath and a shower (power shower although not long), and the washing up, plus handwashing. If we both have showers there will still be hot water for the next day. BUT we make a point of not doing endless bits of washing up. Doing that means that you are running cold water into the tank each time and is incredibly wasteful if you are reheating it.

you knew the property was draughty when you rented it, but thick curtains and draught excluders can work wonders. You can get curtains from charity shops and can always take them with you when you leave.

also - what is your unit cost and standing charge? Can you do better?

yomellamoHelly Thu 25-Jun-15 13:47:32

We have a modern Vaillant with a megaflow cylinder. It takes 15 minutes to heat up the water from having none. That's generally enough for a couple of showers and a bath and whatever small uses we make of it over the day. If we have people staying we'll give it a boost. Water will still be hot next day if we don't use it, in which case it'll take less time to heat the water. (We have a mode whereby it heats the water and then switches on the heating once it's done doing that.)

CountingToThree Thu 25-Jun-15 13:56:13

ours is on one hour in morning and one hour in evening - this covers morning power showers for dh and me and evening baths/ showers for dd and ds plus washing up/ washing hands etc.

BabCNesbitt Thu 25-Jun-15 14:04:41

Thanks for replies. Ours is a Vaillant Ecotec Pro 28. I'm going to try just an hour in the morning and one in the evening, to see if that works. Can't believe I didn't check the timer for the hot water before... Could it be that that's caused our astronomical bills?

specialsubject, I didn't know it was draughty when we rented it - we were moving from overseas and needed somewhere furnished near work to move straight into when we arrived, and this was available. We have thick curtains over the single-paned windows in the living room and a similar one for the door, but it was still absolutely freezing cold from draughts whisking down the chimney (which we can't block up as there's a gas fire).

PigletJohn Thu 25-Jun-15 14:58:04

A hot cylinder is likely to be more economical to run than a combi.

As a Megaflo is well-insulated it loses little heat.

The boiler will be more economical if it does not keep running for short periods to top-up. The thermostat in the cylinder will turn off the boiler once it is hot.

I presume it is quite large, so set the timer to run HW for half an hour or so before you get up in the morning, and again in the evening before bathtime. If you have several users and the hot water runs out, set the timer to run before and during bathtime. Let the timer go off afterwards. There is likely to be enough stored hot water to last all day. If your daily usage is less than the cylinder holds, just run it once a day for about half an hour.

Hot pipes, especially those between boiler and cylinder, should be well-insulated with Climaflex or similar. Use the thick Regulation grade if it will fit.

PigletJohn Thu 25-Jun-15 15:03:28


I would like to know how much gas you use, calculated from your meter readings (not your bill which is likely to be averaged out over the year and might contain estimates).

If, in summer, your radiators are cold and gas usage is a cubic metre per day or more, you probably have a leaking or dripping hot water tap or pipe.

If your room thermostat for the radiators is set to 15C or less, the heating should not come on. You do not need to turn off radiator valves unless there is a fault.

BabCNesbitt Thu 25-Jun-15 15:13:09

Our heating was still set to come on for an hour in the morning and a couple of hours in the evening (mainly to dry clothes when the weather's been bad, though we get no direct sunlight on either side of the house - it's switched off now it's a bit warmer!) Thermostat at around 18C. No idea what the most recent gas usage is as I've supposedly shifted to paperless billing but there are no bills to view online at the moment! But my most recent meter reading (today) was 7856 and on 8th April it was 7580, if that means anything to you?

Ludways Thu 25-Jun-15 15:24:24

I have our water on once a day at 6pm for an hour. Occasionally I'll need to flick the switch to top it up but that's not very often as we rarely run out of hot water and we know we're doing it at the time. Our shower is electric.

prepperpig Thu 25-Jun-15 15:31:34

We only put the hot water on when we need it. It goes on for an hour every morning. That will do a shower for each of us (four in the house) plus warm water in the taps throughout the day if we need it (which we don't really) and then a bath in the evening.

I don't actually think £250 a quarter is that bad but I guess it depends on the size of the house.

PigletJohn Thu 25-Jun-15 15:39:18

"But my most recent meter reading (today) was 7856 and on 8th April it was 7580"

by my reckoning that is in the region of 3 cubic metres per day, which is a lot in summer. In winter you will use several cu.m each day. A cu.m contains roughly 11kWh and costs about 30p. You will also have a standing charge which for gas is about 25p/day

Perhaps you still had the heating on in April or May. Take it again in a week, and then monthly, and write in on your calendar/diary/spreadsheet where you can refer to it frequently and will not lose it.

specialsubject Thu 25-Jun-15 16:25:40

you rented it without seeing it? The EPC should have told you something about the windows, they usually recommend energy improvement measures which tells you what isn't there.

anyway, if it was the only place that suited, that's that.

do speak to the landlord to see if anything can be done (safely) about improving the chimney draught. And do look at your tariff.

BabCNesbitt Thu 25-Jun-15 17:06:11

Thanks, everyone. PigletJohn, I'll keep an eye on the usage and try and work out what the usage is over the next few weeks, and see if it seems excessive, especially now I've cut back on heating the water!

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