Inline water heaters

[Christian McArdle]

I'd like a inline mains pressure electric water heater for my kitchen. However, I want to run it off the hot supply. The line to the heat bank in the loft is around 20m, much of it in 22mm, so it takes an age for hot water to come through. I'd just like to electrically heat until the hot water comes through. I don't want to run a pumped return line for energy efficiency reasons.

When the hot comes through, I want a thermostat in the heater to cut the power. Is there such a device available cheaply?

3kW should be enough (less if storage). I only want to wash my hands or rinse something. If I'm filling the sink, I can wait for the proper heated water to come through. I suppose it could be a storage unit or instantaneous, provided it can feed a standard mixer tap at mains pressure.

Christian.

[Andy Hall]

I have a feeling that to get reasonable flow of reasonably hot water, you are going to need some level of storage. If you consider how poor an electric shower is using 10kW, then 3kW is not going to be at all good, although admittedly, since the water supply is going to be inside the house, you would only be heating the water from, say, 20 degrees to perhaps 50 degrees rather than from 5 degrees. This is probably going to imply a storage device of some sort.

Just as a thought on this, have you thought to consider the energy required to maintain the water in a stored electric heater like this at electricity unit prices, vs. running an insulated, pumped loop heated by gas? I havne't done the sums, but there might not be anything in it.

.andy

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[Christian McArdle]

I'm not so sure. I only want it for handwashing. There are many instantaneous handwash units at the 3kW mark. If I want more than that, I can just open up the tap and wait for proper hot water. I also want it as cheap as chips. Perhaps I could modify a cheap bottom of the range shower with an additional flow switch. Running a new cable to the consumer unit would be simple. The problem is that I need something that doesn't restrict flow too much, as I don't want to reduce the flow rate when it is running off stored energy.

I don't imagine that a 7 litre hideaway unit will lose that much energy. There is space for a lot of insulation. The pumped loop would be a nightmare to install as well. It has to go up two floors and across the length of the house. If I did it, I'd replace by 15mm rising main with 22mm and use the

15mm for the loop, but there is no opportunity to add insulation to the existing pipework, which is buried in the wall, so it would be an energy efficiency nightmare. It can't be surface mounted and boxed in, either, as it runs up the centre of a wall.

Christian.

[Nick Finnigan]

If it is more than about 40w you will probably have other worries, especially in summer. 20 quid a year running costs make it hard to justify buying a fancy shower unit. A 7 litre store with a tiny immersion heater?

[Andy Hall]

I see what you're saying. Might be a tall order.

The instant heaters all seem to be of the 7kW+ rating, storage ones at

3kW. Some have restrictions on the type of tap you can use - e.g. not mixer taps or require vent taps. They warn about not having non return valves on the feed side.

I looked at the installation instructions of a couple like the Triton and they talk about flow restrictors. Perhaps those could be left out. I couldn't see anything that said that you can't use a hot supply as the fee, but nothing that said you could either.

Would it perhaps be more practical to take a cold feed and then run the output to a separate small tap like the kind used for fitted water filters. I've seen these used in the U.S. and in Germany quite effectively.

With all of that hassle it isn't worth it.

.andy

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[Christian McArdle]

It's certainly the obvious solution. Unfortunately, I doubt it would go with the general old oak and range cooker theme of the kitchen. The current taps are burnished brass with "Chaud" and "Froid", and old style handwheels. (Still ceramic cartridge, though, I hate compression valves!)

Besides, any guests would starting filling up their glasses from the handwash tap!

I'm inclined to agree. Unless I can find a simple bolt on inline 3kW heater for around the 50 quid mark, I think I might not bother.

Christian.

[John Stumbles]

IIRC December's plumbing trade mag (voted saddo read of the year in a recent uk.d-i-y poll ;-) had a couple of ads for pipe heating tapes for keeping water hot at the taps between draw-offs. If I could find the mag in the clutter here I'd give you some more details.

-- John Stumbles

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-+ I read a book on improving your memory but I've forgotten what it was called

[John Stumbles]

Got it (Professional Heating and Plumbing Installer Dec'03) page 42:

Flexelec offers range of self limiting heating tapes .. cost effective instant hot water .. aplied under insulation

and

Heatsafe cable systems 'Hotwat Pipe' electrically heat traced & thermally insulated pipe keeps water at 50 - 55C ... PEX pipe, intelligent self-regulating heater & thermal insulation

no contact details - circle readerlink 433 and 435 repectively. PHPI email [e-mail] might help

-- John Stumbles

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-+ a town is never big enough to support one lawyer, but it can always support two

[Christian McArdle]

Unfortunately, the pipe runs immediately into a channel in the wall under the plaster. No chance of insulation. And I'm not replacing the run through the loft space, even if it means the old run can be used for the condensate drain!

Christian.