Hot water immersion - short bursts or 24 hours?

ianpwilliams

I know that this has been asked before but I couldn't find a definitive answer...

Does anyone know how much more electricity is used (in a rough percentage ideally) from keeping the hot water immersion on 24 hours a day, as opposed to just switching it on every day for short periods?

I work 9-5 now, and I have to have it on for an hour very early every morning to run a bath (I leave it on until I leave the house so there is still hot water after the bath), and by the time I get home in the evening the water is stone cold again, so that's another 15 minutes. So I wonder if I might as well just have it on all the time instead.

2010

I can`t give figures but if anything is running 24/7 it must be using more power than a 30 minute short burst.

OK it won`t be running exactly 24 hours because of the thermastat but it will be running above 2x30 minute sessions.

dogshome

If you have an ECO meter, it should be cooking up Hot water overnight on the cheap rate and be full of hot water each morning
It should also have a Booster switch to cook Hot water during the day, only switch this on if you are desperate as it will cost serious money

If you have a Standard meter, but from your post a poorly insulated tank, cook up enough only for your needs as you need it - There is no point in letting it run on if it goes cold before you can use it.

It would be well worth while beefing up the Insulation around the tank

sheffield_lad

Depends on the size of the tank and the type of insulation but over a typical 24hr period an immersion is on anywhere between 4-6hrs.

Best way to work out which way is best is to experiment. start in a morning and check what the meter is on use the immersion as you do now and record how many units you used the next morning again (same time). Then set the immersion for 24hrs and see what kind of difference you see.

I would also find anything you can to wrap it up in old blankets or quilt over the existing insulation will improve the water temp and stop the immersion from being on as long.

macman

A tank jacket costs peanuts and takes 5 mins to fit-you don't appear to have one!
And a timer would help too.

grahamc2003

ianpwilliams wrote: »

I know that this has been asked before but I couldn't find a definitive answer...

Does anyone know how much more electricity is used (in a rough percentage ideally) from keeping the hot water immersion on 24 hours a day, as opposed to just switching it on every day for short periods?

I work 9-5 now, and I have to have it on for an hour very early every morning to run a bath (I leave it on until I leave the house so there is still hot water after the bath), and by the time I get home in the evening the water is stone cold again, so that's another 15 minutes. So I wonder if I might as well just have it on all the time instead.

It depends on the heat loss from the tank, and that depends mainly on the level of insulation.

The very latest and best eco tanks/heat stores (that is, designed with asgoodasyoucanget insulation lose typically 1kwh/day as an absolute minimum (and even that depends on the temperature set for the hot water - the higher, the more is lost).
I'd estimate a large uninsulated tank (like my parents had when I was a kid) with the water set very hot (ditto) could lose about 20kWh/day.

It sounds like yours is very poorly (or not at all) insulated - you should certainly have some hot water left from a full tank after say 10 hours. In the 1 to 20kwh/day range, I'd guess (from the very limited info provided) you'd lose about 10kwh/day if you kept the immersion on all the time. So probably £1.40 per day, as opposed to something like 28p/day from turning it on and off as you need it with your current usage.

Obviously, you need to really beef up the insulation irrespective of how you actually use the immersion. If it already has an old (largely ineffective these days)'jacket', then cover the whole surface with loosly packed loft insulation, and pile plenty on top too.

Probably cost you a couple of quid, with a payback of a couple of days should you keep the immersion on 24/7.

ianpwilliams

I did try to buy a jacket for my cylinder. But the tank is so close to the wall inside the closet, that I couldn't get the jacket round the back. And I didn't think it would be worth insulating just the front! So I'm not sure what to do about that really. Maybe a qualified plumber or someone could sort something out. Not sure how much that would cost though.

I just think that I heat up a full tank (1hr) for a bath, then I use it up, then I heat up another full tank (1hr) to get hot water back after the bath, and then I do a top-up in the evening (15mins). So I do wonder if it really could cost that much more having it on 24 hours than what I'm doing now.

I suppose the best option would be to move to another flat, one with central heating! And a shower would be nice too. Baths are too time consuming in the mornings...

macman

Just cut/pull a section of the jacket away where it's close to the back wall-the jacket should compress down to virtually nothing. You hardly need a plumber to do that for you.
What is the point in heating it up just before you go out for the day, if it's uninsulated?
If you have E7 and are topping it up outside of the 7 cheap rate hours, (typically midnight to 7am) then it's costing you about 350% more.

Richie-from-the-Boro

There's always going to have to be compromise & restriction in a small area. ThermaWrap is a 'best bet' workable solution. Current regs on a bog standard 210 litre allow for a loss of 2.56 kWh loss per [934 kWh pa] day, so you can immediately see the current regs are set at an incredibly low 30%pa value. Any alert and thinking individual fitting a new cylinder would make sure its 90%+ efficiency but government are still at the 70% level with the exception on PartL E7 installs. Get one of these cheepo's and you'll soon find that even with ThermoWrap the boss and pipework losses remain high, so if you are going to make the worthwhile investment in lagging the tank .. .. go the extra mile and do the pipework too.

My point ? - you could get two not one layers of ThermoWrap in the same space it takes to put one el-cheepo insulation jacket if you can afford it, if you cant afford the good stuff at least fit the el-cheepo.

ianpwilliams

Ok thanks for the advice everyone, I shall see what I can do in the current circumstances!

Cardew

As stated above the heat loss from a modern well insulated HW tank is small. The are tested to a British Standard, and the loss in 24 hours with the water at 65C is typically around 2kWh in that 24 hours.

It is also pertinent to point out the that 2kWh heat isn't 'lost' as such as it heats the fabric of the house, which is why HW tanks are usually in airing cupboards.