Electric water heating

wickywocky

My mum's recently bought a retirement flat. It's got electric storage heaters, which we're not looking at replacing, and the hot water is provided by a traditional immersion tank with cold water tank above it. We're changing the bathroom to a wet room with an electric shower, so her only hot water requirements are for the kitchen sink (including washing up as she won't have a dishwasher) and bathroom hand basin (which is the other side of the wall to the kitchen sink). There isn't a gas supply and we wouldn't be able to get one.

The immersion tank and accompanying cold water tank are huge, and don't provide much in terms of hot water pressure. She would ideally like a pull out tap so she can fill a bucket without having to lift the bucket it out of the sink, but the one's I've seen that say they work in low pressure systems don't specify how low. The tanks are also a little distance from the sink, so you need to run about half a bowl full of cold before the hot comes through. And they take up a lot of space in a small flat and as she's going from a 3 bed semi into it she has a lot to store!

I've had a google and found multipoint undersink instantaneous water heaters. Would one of these be a good solution? What are the comparative costs of heating a huge tank of water on economy 7 compared to heating just the amount we need on a regular tariff? Is there something else we should be looking at?

Thanks in advance

Relbs

I'd also like to know the answer to this- my mum is in the same situation- except she has a dishwasher, so just needs hot water in the bathroom sink.
My husband look online and found this: Heatrae Sadia Multipoint Instantaneous (can't post link, sorry)

Does anyone know if it's any good?

Thanks

lstar337

wickywocky wrote: »

I've had a google and found multipoint undersink instantaneous water heaters. Would one of these be a good solution?

You need 9kW+ for a decent flow, and even that would not be great. It will also need it's own wiring from the consumer unit as it is such a high power device. It will suffer damage if you are in a hard water area too.

wickywocky wrote: »

What are the comparative costs of heating a huge tank of water on economy 7 compared to heating just the amount we need on a regular tariff?

It will be very expensive (as expensive as the shower) during peak electricity hours. E7 will not be much help as that will be during the night. If you come off of E7, you will need to ditch the storage heaters as they are only really economical on E7. This would be a bad idea in my opinion.

wickywocky wrote: »

Is there something else we should be looking at?

The tank you have with E7 will be your cheapest solution. I know it sounds backwards to heat a lot of water when you don't think you'll need it, but trust me it is the best solution.

The tanks are designed to heat the hot water over night and keep it hot (check the insulation on the tank and if there is space add another jacket). Once the water is up to temp, it will only take a little bit of cheap (~7p/kWh) electric to top it up each night after.

If you want to rip it all out your costs are:

Plumber + labourer to rip the whole lot out.
Plumber + electrician to install instant hot water unit.
Cost of hot water unit.
Ongoing cost of peak rate (~18p/kWh) electric to power it.

Additional cost may be:

Supplier to swap meter to single rate.
Electrician to re-wire all off-peak consumer unit to single rate.
Ongoing cost of running storage heaters on single rate (~12p/kWh) electric, or cost of replacing all storage heaters with panel heaters which would still cost a fair amount to run on single rate.

There is a reason night storage heating was designed and installed in properties, electric heating is expensive and night storage is the only economical way to do it.

Sorry if that sounds like a truck load of bad news.

If you want additional information on making the most of your heaters and hot water efficiency there are lots of posts on the forum by myself and other users. Or just ask in here and I'll try to give you some useful information.

lstar337

Relbs wrote: »

I'd also like to know the answer to this- my mum is in the same situation- except she has a dishwasher, so just needs hot water in the bathroom sink.
My husband look online and found this: Heatrae Sadia Multipoint Instantaneous (can't post link, sorry)

Does anyone know if it's any good?

Thanks

Don't know the set-up of your building, but the advice I posted above probably fits for you too.

wickywocky

Thanks for your reply lstar337

Just to clarify, we're not thinking of changing the storage heaters and getting rid of the Economy 7 for them, it's the water heating that is our main concern.

Adding a new circuit should be quite simple. The consumer board is likely to be upgraded anyway as we're refitting the kitchen and bathroom and getting a new shower and induction hob, and so we'll have all the trades onsite anyway.

Relbs, if you're looking at instantaneous water heaters, check that they are ok for kitchen sink installations. Some of the ones I looked at said (hidden in the tech/installation specs) that they are not. I'm not sure why. This is my favourite of the one's I've looked at so far stiebel-eltron

lstar337

wickywocky wrote: »

Thanks for your reply lstar337

Just to clarify, we're not thinking of changing the storage heaters and getting rid of the Economy 7 for them, it's the water heating that is our main concern.

Adding a new circuit should be quite simple. The consumer board is likely to be upgraded anyway as we're refitting the kitchen and bathroom and getting a new shower and induction hob, and so we'll have all the trades onsite anyway.

Relbs, if you're looking at instantaneous water heaters, check that they are ok for kitchen sink installations. Some of the ones I looked at said (hidden in the tech/installation specs) that they are not. I'm not sure why. This is my favourite of the one's I've looked at so far stiebel-eltron

Well it sounds like you have already made your decision.

Just bare in mind that you will have less water that costs more money if you decide to go ahead with instantaneous water heating.

If you are not going to use a lot of water then boiling a kettle would be much more cost effective.

amtrakuk

I used to have a 12Kw Redring Power stream. It was great for hot water in the summer but in winter you really had to turn down the tap to get any heat. Doing an A/B comparison 12Kw only raised the ambient temperature by 20 degrees C at full stretch (1-1.5 Gallons a minute). also bear in mind you will need to get a sparky in to wire a 50 Amp fuse into the setup.

If you want a good flow go for a "thermal store". It's inherently safe as works at atmospheric pressure so no annual servicing needed or safety valves AND can (as we have ours) located in the cellar. Oh and you get mains pressure hot water. I have mine heated by 2 x 3Kw immersion heater elements with immersion timers - although we only use the bottom one.

Think if it as a combination between a battery and a Coffee cup. If you stick your finger into a hot coffee cup your finger will get hot. now imagine your finger being replaced by basically a pipe coming in at the bottom of the coffee cup and out at the top and on to your taps.

As you turn the hot tap on cold water will flow at mains pressure though the pipe in the thermal store absorbing the heat as it flows and then out to your tap - and can be VERY hot if you want it - but it will use up the reserves quicker. We have ours set at about 40c. The "jacket of water that fills the cylinder never mixes with the water that comes out the tap unlike a traditional cylinder

I have a 200 litre cylinder with 100mm of insulation. It comes on for an hour in the morning and an hour in the afternoon to top its heat reserves up. It easily handles the demands for 2 showers and washing up. At the weekend It is on from 8-8 running on thermostat and unless were being stupid we never run out of hot water.

We got ours here http://www.navitron.org.uk/product.php?proID=90

As an extra got an integrated header tank to keep the heated "jacket" of water topped up, also upgraded insulation.

Richie-from-the-Boro

The standing heat loss of a Part L - E7 water cylinder [how effectively it can store energy per insulation] was very good even before the 2010 regs changes. A standing loss per 24 hour cycle of about 2.5kWh even on a big 150 litre domestic tank. The costs outlined by 'lstar337' suggest its uneconomic to destroy an effective working hot water system :

- and replace it with a less effective hot water system
- the 2.5kWh/24 is not heat lost, that heat goes into the dwelling
- with negative unnecessary costs removing the E7 cylinder, control and wiring
- with negative unnecessary costs putting in a~n~other alternative system
- with negative unnecessary costs at 3 times the price of the energy needed

You decide ............. seems like you are looking for an expensive solution to a problem that does not exist.

Relbs

Thanks for the replies. For my mum, the issue is space. The flat is very small, and has 1 storage cupboard, half of which is taken up by a MASSIVE hot water tank. We are looking for a solution that would get rid of the tank. She has an electric shower already fitted, and a dishwasher, so really only needs hot water in the bathroom sink. She lives alone so is only going to be using a small amount of water. It might be less economical, but she needs the space in the cupboard. It does seem a bit crazy to heat a large tank of water, only to use 1-2 pints/day for hand washing.
Any other suggestions?

lstar337

I fail to see how removing even the largest tank is going to free up much space.

However if you must do it and it is for small amounts of water, then at work we have one of these: http://www.hyco.co.uk/product.asp?id=177

It's a small un-vented cylinder that holds a few litres of water. It can go into a normal plug socket as it is low powered.

I would stick with what you have, but the above unit performs fine for us. Of course we don't worry much about what it costs as we have many high powered machines that make much more of a difference!

Smiley_Dan

If it's just for a basin can't you just use one of those small hand wash units like http://www.plumbworld.co.uk/triton-t30i-hand-wash-unit-3kw-576-21962 ?

For hotter water such as instant boiling water you need a buffer under the sink.