Electric water heaters (non storage), low pressure?

Does anybody know of a particular model of "undersink" type low-power electric water heater which is designed for a low-pressure water system with header tank, not mains pressure?

I seem to be struggling to see anything online which clearly states that it is (a) for water systems at header-tank pressure only and (b) does

*not* have hot water storage but only provide instantaneously heated water.

Any particular model names much appreciated.

Michael

Reply to
Michael Kilpatrick
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Reply to
Dave Osborne

You just need to look at the minimum pressure requirement of the heaters and then you will see what will work...

For every 10 meters of "head" you have (The height of the cold tank in relation to the tap) you have 1 bar of pressure.(So 10m is 1 bar, 5m is

0.5bar, 2.5m is 0.25bar etc...)

Toby...

Reply to
Toby

keen on you only fitting their own taps or shower fittings to their heaters. I've just been dealing with another make and model of this type of heater which has been giving problems because it is prone to tripping its overheat cutout thermostat. Resetting this involves opening up the box so it's a hassle for the user. This particular unit is described as an "INSTANTANEOUS HAND WASH WATER HEATER ... that can be used with either taps or an open outlet sprayhead". It's actually feeding a washbasin, sink and commercial washing machine but only seems to trip when the latter is drawing from it (so I am told: I've never been there when this happens).

Presumably there is a certain tolerance on the sensitivity of the flow switch that tells the unit when to switch on and off, and on the temperature at which the overheat cutout is set. At flow rates just above the turn-off rate (which due to hysteresis(sp?) is a bit below the turn-on rate) I've measured the water temperature at 80C, which must be close to the overheat trip temp. Presumably under certain circumstances the washing machine induces the heater to get up this sort of temperature then cuts off rapidly enough for the residual heat energy in the heating element to take the temp up enough to trip the overheat.

Apparently the more powerful 12.5kW model in this manufacturer's range (this is a 9.5kW unit) has a thermostat operating to cut out one of the two heating elements at high output temperatures, but this model relies on the flow switch alone (even though it also has two elements). I suspect the Redring unit which stipulates you use its own taps relies on these always providing sufficient flow rate to keep the outlet temperature down. And of course that means you could not fit a TMV to regulate the outlet temperature as that would throttle the heater output.

So overall I think some of these units may be a poor design for practical use.

Reply to
YAPH

Indeed...but a lot of the listings online don't give full information. Can't see the wood for the trees.

There will be a fairly low head. It's a bungalow.

I'll explain - we insist on having a *proper* bidet in our new en-suite. Not those stupid over-rim fill units but a proper ascending spray bidet. There used to be one in the old main bathroom fed from the vented hot water cylinder sytem and the cold water tank. That gave a perfectly adequate head for the spray.

Unfortunately the ridiculously overbearing regulations make it very difficult to fit a proper bidet these days - and our new heating/water system features an unvented hot water cylinder which of course is coupled directly to the mains.

In order to fit a proper bidet we would need to install a small header tank in order to have an air-gap isolated water supply, and in order to get hot water for the bidet therefore the only practical option is to have a small electric heater fed from that header tank. A storage heater would be a waste of energy given the low frequency of use. The amount of hot water use is minimal, so something that is a 5kW instant heater is all that is required.

Seems difficult to find something as simple as this!

Michael

Reply to
Michael Kilpatrick

What a pain!!

Wouldn't they be happy with a double check valve on both the hot and cold supply to the bidet to prevent anything nasty getting back into the mains supply? Seems pretty OTT if not to me, as as far as I am aware, you can fill your pond with the hose if you have a double check valve!

Toby...

Reply to
Toby

Yes, it's all a load of tosh if you ask me. A bidet is a "category 5" fluid risk, and for some reason a double check valve is not sufficient. You have to have an air gap e.g. cistern with ball c*ck valve. Or something called a type DC pipe interrupter, but I'm not really sure about those when attached to a bidet.

Absolute twaddle, it really is! Anyway, I never had a double check valve on our outside tap, as it wasn't a requirement when the house was built. And I've connected it directly to a hose whose outlet is submerged in the fish pond.

Michael

Reply to
Michael Kilpatrick

because basically you could crap[1] into the bidet pan and it'd be equivalent to a fresh, potable water supply pipe, shared with the neighbours's drinking water taps, submerged in your khazi.

Loadsamoney, but probably in the Reliance Water Controls catalogue.

Maybe not if you're the neighbour whose drinking water tap is on the same supply as your bidet/khazi.

[1] or more politely, and realistically, faecal matter could get into it.
Reply to
YAPH

I know peoples' gas boilers can explode. I know houses can catch fire (I've seen it happen in front of me). I know radiators can leak and ruin a carpet or worse.

The thing is, I've never heard of anyone who has experienced, or indeed has ever told me of anybody else who has experienced, backsiphonage through the water mains.

Furthermore, whilst I might occasionally leave a tap running in a basin, it's rather a different matter to leave an ascending spray bidet running inadvertently and unattended, which is when a risk of backsiphone might be present.

Michael

Reply to
Michael Kilpatrick

You might be using the bidet when Fireman Sam comes along and attaches his water pump to the hydrant down the road, dropping the pressure to your house and sucking the water and unmentionables back out of your pipework into the common main. Then Sam turns his pump off and Mrs Jones down the road finds she can fill a glass of water again ...

You might (fairly reasonably) say what are the chances of that happening, but from the point of view of the makers of the regulations, if there weren't such a restriction and, say, ascending spray bidets became popular and common over the country there could be a pretty good probability of it happening from time to time. And given the consequences (Mrs Jones isn't too healthy and if she gets topped by the public water supply someone's head's going to be on a pike) it's a reasonable position for the regulators to say: "this water supply, provided at public expense, is intended to be safe for drinking under all circumstances: if you want to wash your botty in it, fine, but you must make doubleplus sure - at your expense - that your botty washings don't get back into the public supply".

Reply to
YAPH

On 28 May 2009 09:26:33 GMT someone who may be YAPH wrote this:-

The chances of this happening when the bidet is fed from the mains and a double check valve is fitted to the hot and cold supply are, I suspect, so small as to not be worth considering. Mrs Jones' house is probably more likely to be destroyed by an aeroplane falling out of the sky.

Is the water supply often contaminated in this way in comparable places with a more relaxed attitude to such things?

Reply to
David Hansen

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