Immersion heater help

Burgerphone

Hi,

I live alone in a flat with an electric immersion heater for my hot water. I'm on a standard electricity tariff so no cheap economy 7 hours for the immersion heater to heat the tank up.

So what I've been doing for the past couple of months I've lived here is getting up in the morning and putting the boost element on for half an hour which gives me enough hot water for a shower and for some washing up. The problem with this is that I have to get up half an hour earlier than I would if I had hot water on demand. The timer is connected to the off peak element which takes longer to heat the hot water (half an hour on the timer/off peak element doesn't give me hot enough water).

Obviously I would prefer to be able to put the tank on a timer so I don't have to get up and put the boost on then wait half an hour. However, it takes about an hour and a half to get the same temperature water from the off peak element than from half an hour on boost. Will this cost a lot more in electricity? I'm not sure how immersion heaters work exactly but I was under the impression that when water in the tank was heated, it rose to the top anyway, so surely it shouldn't make a difference which element is used? Does the fact that the off peak element takes longer suggest that it is using less power but over a longer period of time?

Any suggestions would be much appreciated.

Cardew

Does the fact that the off peak element takes longer suggest that it is using less power but over a longer period of time?

No it indicates it is heating the whole tank, rather than the top of the tank.

IMO people get far too stressed about the cost of hot water heating. Provided your HW tank is well insulated, the losses are quite small. Typically a full tank with water at 65C will 'lose' 2kWh over 24 hours; and that heat isn't 'lost' at this time of the year as it warms the fabric of the house.

You could probably get away with heating the tank every other day.

I suggest that you experiment with using the main element and keep a note of consumption - assuming you can keep the other electrical consumption roughly the same.

The other suggestion is to fit a timer on the boost immersion heater.

Burgerphone

Cardew wrote: »

No it indicates it is heating the whole tank, rather than the top of the tank.

IMO people get far too stressed about the cost of hot water heating. Provided your HW tank is well insulated, the losses are quite small. Typically a full tank with water at 65C will 'lose' 2kWh over 24 hours; and that heat isn't 'lost' at this time of the year as it warms the fabric of the house.

You could probably get away with heating the tank every other day.

I suggest that you experiment with using the main element and keep a note of consumption - assuming you can keep the other electrical consumption roughly the same.

The other suggestion is to fit a timer on the boost immersion heater.

Interesting... So will using the off peak element for 1.5 hours use 3 times as many kWhs as using the boost element for half an hour? I've noticed both elements have a rating of 3kW - does this mean in an hour and a half it will use 4.5kWh?

It still seems like a bit of a faff heating the water on a timer every other day, as then I'd have to remember every other night to switch the timer off/on. I don't really have the DIY expertise to fit a timer to the boost element either...

Swipe

A work around would be to shower at night insead of morning

matelodave

A simple timer can be installed in place of the switch that turns the boost element on & off. The cheapest I've seen is about £11 from Screwfix or you can get one from B&Q, Wickes or even Maplins.

The instructions that come with them are very clear and providing you turn the leccy off at the main fuseboard whilst you do the job it isn't all that difficult.

I'm sure that you've got a mate with sufficient expertise who would do it for you for a pint if you aren't happy to do it yourself.

As Cardew says just leaving your main immersion on will heat the whole tank and then just maintain it at the chosen temperature using off-peak leccy which probably costs half or less than what you are paying for using the boost heater on full rate. Try leaving it on for a week or so to see how much it actually uses and then work out how much it cost compared with your half hour regime in the mornings - you might be surprised.

Make sure the tank is well insulated - put another jacket over the top of the tank (or wrap it with an old duvet/sleeping bag) to keep even more heat in (even a foam lagged one would benefit).

You could also reduce the hotwater temperature - by adjusting the thermostat under the cap of the immersion heater.

Burgerphone

matelodave wrote: »

A simple timer can be installed in place of the switch that turns the boost element on & off. The cheapest I've seen is about £11 from Screwfix or you can get one from B&Q, Wickes or even Maplins.

The instructions that come with them are very clear and providing you turn the leccy off at the main fuseboard whilst you do the job it isn't all that difficult.

I'm sure that you've got a mate with sufficient expertise who would do it for you for a pint if you aren't happy to do it yourself.

As Cardew says just leaving your main immersion on will heat the whole tank and then just maintain it at the chosen temperature using off-peak leccy which probably costs half or less than what you are paying for using the boost heater on full rate. Try leaving it on for a week or so to see how much it actually uses and then work out how much it cost compared with your half hour regime in the mornings - you might be surprised.

Make sure the tank is well insulated - put another jacket over the top of the tank (or wrap it with an old duvet/sleeping bag) to keep even more heat in (even a foam lagged one would benefit).

You could also reduce the hotwater temperature - by adjusting the thermostat under the cap of the immersion heater.

Hi thanks for the advice.

I don't have economy 7, so I don't get off peak electricity. Would it still be cheaper to have the main element on the timer for an hour and a half each morning than using the boost for half an hour every day?

Sorry if that's a silly question...

Swipe

Burgerphone wrote: »

Hi thanks for the advice.

I don't have economy 7, so I don't get off peak electricity. Would it still be cheaper to have the main element on the timer for an hour and a half each morning than using the boost for half an hour every day?

Sorry if that's a silly question...

No, it would cost 3 times more

ChumpusRex

Swipe wrote: »

No, it would cost 3 times more

This assumes that the tank does not reach full temperature, causing the heater to shut off.

The OP hasn't said how big the tank is. But a 70 litre tank takes about 3 kWh to heat up to 60 C, at which point the heater will shut off.

Even if the off-peak heater was left on 24/7, most hot water tanks would only waste about 2 kWh of heat per 24 hours through leakage into the room.

There is a small risk of bacterial contamination of hot water tanks if they aren't regularly heated to full temperature. Given the small amount of energy leakage from hot water tanks (as long as they have a suitable insulating jacket), I would suggest setting the off peak timer for maybe 2 hours or so in the early hours of the morning. This way you get a full tank of water for a shower, but because the whole tank was heated, there should still be half a tank full for the rest of the day.