Immersion heater advice needed

Roohster

Hi all,

Does anyone know if it is more efficient to leave an immersion heater on 24/7 than having it on a timer?

My landlord has had our flats fitted with new heaters, the builders ripped out the timer without even telling me.
The plumber has informed me that modern heaters are so well insulated/efficient that we should just leave them on.

It seems crazy to me to leave anything switched on that doesnt need to be.
Previous to the new installation I had a timer that heated the water for an hour or two in th eearly hours of the morning and was plenty to last me all day.

If be grateful for any advice before I hire someone to come and reinstall a timer.

SteveCritten

There are various for and against's(if that's a word haha). I remember hearing years ago that it's better to leave on all the time but it was disproved in certain scenarios. If the building is well insulated and sealed then using the thermostats on individual radiators and leaving on 24hrs is more efficient otherwise it's not.

dav-t

I'm an electrician , it makes absolutely no sense whatsoever regardless of the insulation or anything else to leave a near on 3 KW immersion heater on permanently . the only scenario to leave it on would be if hot water was required 24 hrs a day, otherwise put it on a timeswitch
regards
d

SteveCritten

? Why not? There is simple logic why you should be able to. As you know it will not be using 3kwh all the 24 hours.

Roohster

Thanks Steve, but I'm not sure that applies as it's only an immersion heater I was enquiring about, not radiators.

And Dav, my thoughts exactly.
Just before the timer was removed I was using it with the new boiler.
I had it set to come on for an hour in the early hours, and this gave me enough hot water to last all day.

SteveCritten

Yes mate I was confused, I was thinking of heating but it also applies to immersion. As I say there are mixed ideas of which is best.

dav-t

if like you say an hour was enough for you ,then you will be throwing money down the drain,get a time clock back in line quick
rgds
d

DPinBucks

A tank of hot water, no matter how well insulated, will be constantly losing heat and cooling off.  The better the insulation, the slower the process.

An immersion heater will automatically switch to replace that heat when the water cools to a pre-set temperature.

You don't need hot water during the night, but you do need it in the morning.  So any power used to keep it hot overnight is wasted.

The most efficient solution is to switch the heater off sometime in the evening so that the water when you go to bed is just hot enough to use.  Then it should switch on in the morning just in time to get it hot enough for when you get up.  The first part is easy to establish by experiment; the second less so because you're asleep.  The better the insulation, the less difference timing adjustments will make, because you're not losing much heat anyway.

The best bet is to try it one night: switch the heater off as usual, but don't switch it on again overnight.  Then see how hot the water is in the morning.  If it's still hot, then you have good insulation and a timer will make only a little difference.  If it's lukewarm or cold then (a) you need a timer; and (b) you ought to get the tank better insulated.

You should also not let the water get hotter than you need; that's also wasteful.  Turn the thermostat down a notch and see how you get on.

The bottom line is that a timer will always make a difference, but how much of a difference depends on the insulation and how hot you like your water.

SteveCritten

But I thought the theory was that it takes more energy to warm up cold water than it does to keep topping already hot water up. As you say it depends how insulated the tank is but when I experimented a few years ago the difference was insignificant to not be sure which way worked out the cheapest, but for me being on call 24/7 I may need a wash at any hour I just leave my hot water on permenantly. My tank is a pressurised system(even more efficient) and very well insulated so the amount of times the boiler kicks in is minimal and heats up very quickly. I believe there has been many "experiments" by better men than me and the jury is still out so I do think it will depend on how good your system is. I certainly wouldn't try it on one of the old tanks with just a thin red "blanket" round it.

neilball

Simple physics says that heat loss is proportional to temperature difference, the higher the temperature difference the higher the heat loss and therefore energy waste. When the tank is hot you have higher standing losses from the pipe work close to the cylinder too.

You would not leave your boiler switched on 24/7 with the only control being the boiler thermostat just in case heat is needed, so why leave the hot water heating on 24/7. If you need hot water in the middle of the night then the tank is still relatively hot providing you did not run off all the hot water from when the immersion was last on.