Boiler for electric-only flat

AngelaDub wrote: »

Our electricity bill was very high so we switched off the heating and it dropped by a third and then switched off the immersion heater water tank and it dropped by another third to about 40 GBP per month. We now regularly check the meter and keep the immersion heated water off. (Heating off too.)

Before investing a lot of money in a new system you'll need to do some maths to make sure the cost is justified by the benefit. There may be some other low cost things to do to cut your bills without much outlay.

In your first post you said switching off the immersion heater cut the bill by 'another third' to about £40 per month. First off, is this bill based on actual consumption during the month, or is it the amount of your direct debit which may reflect previous higher consumption? Is the 'third' accounted for by the immersion heater actually £40 - i.e. your original bill was £120?

That's the first issue of concern - if the immersion heater is costing £40 per month then assuming a cost of about 7p/kWh for E7 electric then it would be using over 18 kWh per day - a typical immersion heater is about 3kW, so it would need to be running constantly for over 6 hours a day to cost that much.

My 3kW immersion heater will fully heat a standard size cylinder from cold in about 3 to 4 hours. So there's either something wrong with the figures, or something wrong with your immersion heater.

You need to narrow down the cost of running the immersion heater - if it is on a timer correctly limiting it to the E7 hours of your meter, your storage heaters are off, and you use minimal other electricity during off-peak hours, then the 'night' meter readings should give a fairly accuate measure of the amount of electricity the immersion heater is actually using. Checking the 'night' readings every day for a week or so will give you a good idea of the cost (excluding the standing charges you'd have to pay anyway) of actually using the immersion heater.

The cylinder insulation is obviously poor, but you should also look at insulating the hot water pipes, especially the first couple of metres from the draw-off point on the cylinder. I would also want to check the pipework some time after you last use any hot water to make sure the hot contents of the cyclinder aren't circulating around the pipework and keeping it warm to the touch - it shouldn't happen, but it sometimes does.

The other thing to get checked (but you'll need an electrician to do it) is whether the immersion heater has a thermostat. If not then it will run continuously all the while the timer is 'on'. Not only is this wasteful but it is also potentially dangerous. If there is a thermostat, is it set to the right temperature and actually working?

If you have a correctly working thermostat the immersion heater will heat the contents of the cylinder and then switch off. My hot water will then remain hot enough for washing up up to 48 hours later, that's with a pre-lagged (but old) cylinder, but with the insulating jacket correctly fitted to yours then you should have hot water for washing up at least into the evening.

Finally, rather than changing the size of your cylinder, one way of reducing electricity use is just to heat a smaller amount of the contents. If you do only have an immersion heater in the bottom of your cylinder the following won't work, but if you have a top fitted immersion heater and it is only a short one, then it will only heat the water you need for face and hand washing and washing up. This is what I do, and in the summer my hot water - including a quick shower - costs under 12p per day.

If you do go ahead with changing the cyclinder then having one with both top and bottom heaters will help you minimise running costs. And if you can put up with the slight inconvenience of having to plan ahead or waiting for the water to heat up, then only heating the whole cylinder when you actually have the occasional bath (even at day unit prices) may work out cheaper than always having a bathfull of hot water on standby.

molerat wrote: »

The other problem you have with that tank is the low head (from the header tank on top of it) meaning low water pressure, not very good if you want a mains shower - in fact you probably can't run a shower from it at all. A new unvented cylinder would give you a better pressure - is your cold water pressure good ?

If anything like my old flat (it probably is) the shower is connected directly to the mains inlet anyway. They wouldn't run it off the header tank when it is that low. I wouldn't go to the trouble of an un-vented cylinder, they are more money and trouble than they are worth.

AngelaDub wrote: »

@molerat The hot water pressure is terrible, especially in the kitchen! The cold water pressure is good.

Yes, that isn't likely to change tbh. I had the same thing in my old flat. The tank/header were on the same floor as the hot taps, so not enough 'head' to push any kind of real flow through the tap. (you may find a new part-l cylinder is slightly taller/thinner giving you a small increase in flow).

AngelaDub wrote: »

We would love higher hot water pressure - can the unvented cylinder still work to take advantage of Economy7 and be on a timer switch, etc. ?

Your choice, but I have seen enough posts on this forum about un-vented cylinders to keep me away from them for ever.