electric cold-feed showers.

[kdband]

Hi, My current shower is electric with a cold-water only feed and is getting rather old. I think it is 7.5 Kw but I'm not 100% sure. We are finding that at this time of year it is barely able to heat the water to an acceptable temperature. We have very good mains pressure and usually have to reduce this by running a tap at the same time as the shower in order to give the unit time to heat the water before it leaves the heat echanger. I am thinking about replacing it but if I do this it would have to be like for like at the moment. By that, I don't mean I want to replace one poor shower with another but if I do replace it now, then the new one will also have to be electric cold-feed only. I know people will want to try and convince me about Mixer showers and Venturi showers but I haven't got the time to start messing around with the plumbing at the moment. I want to take the old unit off the wall and put a new unit in its place, otherwise the job will have to wait for a while and we put up with cold showers.

So the question is, can anybody recommend any reasonably priced electric cold-feed only showers which might be able to cope better than the one we have now? I was thinking that a higher wattage shower might have a better chance of heating the very cold water before sending it to the showerhead. B&Q currently have a 9.5 Kw Gainsborough at =A364.98 or a 10.5 KW Gainsborough at =A389.00. Are either of these any good or should I avoid them like the plague ? I don't mind spending more if I have to, the momey will not be waster as whatever I install now will almost certainly be moved into the En-suite when I eventually get around to building it.

TIA.

Kevin.

[manatbandq]

?

That's what the temperature/flow control knob is for!

MBQ

[Stefek Zaba]

Basic physics prevents you getting anything massively better. Instant electric showers are just about 99% efficient - essentially all the electricity they consume goes into heating the water passing through, with only small amounts lost through heating the wall they're mounted on and the surrounding air. Given that, uprating from a 7.5kW to a 10.5kW one is adding another (3/7.5)*100% = 40% of available power - which can be traded off either as 40% more flow at the same temperature, or a 40% greater temperature rise at the same flow rate, or anywhere inbetween.

Then there's upgrading the cable to supply 40% more power; it's likely your existing cable is sized for a 7.5kw (just about 30A) load, while a

10.5kW 'monster' will be pulling about 42A. To a first approximation, this usually means replacing a 6mmsq run with a 10mmsq one (and uprating the MCB); proper calcs need doing to be sure, though, depending on circuit length and routing (especially if it goes through thermal insulation...)

Now, if a plumbing-change-free solution is all you feel up to for now, then a heftier-rated shower with the cable upgrade is your only solution; just don't expect magic. And you may want to look into putting a flow restrictor in-line with the new (or even the old!) shower, simply to reduce the flow rate through it to give it more of a chance to heat a necessarily smaller dribble of water to a more acceptable temperature. You may find a more modern instant-leccy shower includes an automagic flow-rate-controller, too, so in winter you get water that's just as hot as in summer on a given setting; just less of it.

'O'-level physics follows: pushing the temp of 1 litre of water up by 1 degree Celsius needs 4.2kJ. A kJ is 1 kW/second; so, over a minute, each kW of shower-rating can raise a litre through about 15 degrees (since it takes 4.2, call it 4, seconds to raise it through each degree), or more usefully for back-of-the-envelope purposes, half a litre through the 30 degrees needed to take 'cold-but-not-freezing' (10 degrees C) to 'warm but not hot especially by the time it's been through the air and hits your skin' (40 degrees). Which gives us the rule-of-thumb that flowrate of showerable-temp water in litres/minute is half the kW rating of the heater - whether that's an instant-electric or a combi (after exhausting any pre-stored reserve). Of course, shower and combi mfrs play fast and loose with their 'flow rate' figures - even if they do give one, it's almost always for an unrealistically low temperature rise (assuming, say, a 20-degree feed - "it's summer!" - and a 35-degree output "it's summer, you *want* a refreshing, cooling, not-too-hot shower!". (Indeed, one of our regular physics-defying brochure-regurgitating posters will be along soon to p-d and b-r; let's not encourage him by arguing.)

HTH - Stefek

[kdband]

Ha Bloody Ha !

[Jim]

Now that you have absorbed all that "claptrap and disposable technical rubbish" Perhaps you should consider that the old unit is completely furred up and can't be compared to the current selections. Maybe you should consider putting the 9.5 kw unit in. Then have a nice shower--a strong tipple--and invite your now cleaner maiden in for the finale. If you are lucky--maybe your own fuse is the only one to blow.

[Christian McArdle]

It is unlikely that the electric feed will support a large increase in power. Your choices are probably to install a new 7.5kW shower, mess around with the electrics to get a 10.5kW, or mess around with the plumbing to get a decent shower.

If you post the length of the cable run, the cross sectional area of the cable and the way the cable has been installed into the building (i.e. run between floor boards, buried in an insulated wall etc), then it can be seen if the circuit is already large enough. However, determining the cross sectional area isn't necessarily very easy. It is probably 6mm2 or 10mm2 cable. It might be as small as 4mm2.

Christian.

[Medallion Man]

I had no end of grief with a Heatrae Sadia, so I replaced it with a Gainsborough on special offer from a shed. *Then* I found out that Gainsboroughs are yesteryear's Heatrae Sadia designs with the casing tarted up and the price dropped to fit on the shelf in a shed.

Within the first year that Gainsborough shower needed a new solenoid valve, the shower head was too restrictive (replaced it with a French one) and it developed a dangerous fault in that one of the crimps of the heater connections was badly made and overheated, which heated the hefty copper cable, which in turn nearly melted through the top of the casing. Gainsborough flat out refused to supply me a spare and instead sent me a fitter who did the job FOC, who mentioned that he saw this fault a lot, and who was under instructions to take the old part away with him. If that doesn't reek of a product liability problem I don't know what does. The solenoid valve is getting noisy again, btw. Short answer to your question: Avoid.

[kdband]

Christian When I posted I was still at work so couldn't be certain about any of these things but now that I'm home I have some of the answers. The current shower is on a 40amp MCB with 6mm2 cable. The cable run is slightly more difficult to determine but the shower unit is relatively close to the consumer unit on the floor above. I would guess that it's no more than 8m long in total and runs under floorboards and up through studded plasterboard. I don't believe any of the studded walls in the house contain insulation but I canot be 100% certain. As it happens I would be much more inclined to upgrade the electrics if needed as this would be much easier given the current state of the rest of the work I'm doing in the house. That said I was rather hoping for the straight swap of one unit for the other. Any opinion as to the largest rated shower I can safely install without running a new cable ?

[quisquiliae]

I also have this problem. The big problem is that the wiring feeding my

20 year old Triton T80 won't take a higher load. I considered rewiring but that is just too much trouble in a flat. So I've decided I may as well install a gas combi instead. (May as well replace the 20 yr old boiler before it fails catastrophicaly one day. Besides reclaiming the area occupied by tanks etc adds at least 5% extra space to a tiny flat).

So my advice, check that a higher rated heater won't overload your wiring.

[jacob]

Calculator here

kw showers are OK giving adequate shower but I would have thought

7.5 kw just too small to be any good. If you are putting in a cable why not go next size up - 10kw needs 10mm cable, go for 16mm and be covered for a bigger shower. I find electric showers very handy - cheap to buy and fit (depending on cable and pipe route) reliable, quick response and always available, but if you want the best then go for mains pressure via combi boiler , but then combis come with a whole load of problems of their own. cheers

Jacob

[T i m]

When you remove your 20 year old T80 could I have it as spares for my

15 year old one please ;-)

Mind you, the last time it went wrong I got a new part straight from Triton?

As posted already it does run out of 'ooommpf' in the coldest weather but is still pretty stable temperature wise and serves it's purpose (heating water to allow us to wash) pretty well.

All the best ..

T i m

[quisquiliae]

Mine had most of its insides replaced ~12 years ago. The local plumbers merchant suggested contacting Triton direct. I did and was able to replace the heating element and valve assembly for about £40 inc vat,p&p etc

It needs more replacement parts now. Switching to the off position there is a sound of water boiling although switching to cold/low/high settings is ok. For the past few months I have been leaving it on the cold setting and switching off at the isolator.

That and a combination of winter weather was about to motivate me to rewire and replace. Then the plumber who came during my kitchen renovation suggested a combi. Which makes sense, with the kitchen done converting the shower room/WC (170cm x 90cm) into a wet room is the nextgreat renovation project. But quote for new HE combi (central London prices) £3,000. Still awaiting the wet room quote... oh and the car service estimate is over £2000 (which must be more than a ten year old Twingo is worth). Sigh -- I need to get out of academia and get a proer paying job; or move somewhere sane and sensible.

Yes in summer setting it at 8/12 is hot enough and reasonable pressure. This week though its at 12/12, and just adequate.

[excuse typos, keyboard needs cleaning]

[Dave Stanton]

You don't run 16mm2 very often in a domestic situation then do you !!

Dave

[simon beer]

We had a mira sport 8kw running on 6mm cable for about 10 years till I finally bit the bullet and put in powershower. Although you can't compare the two my wife was always happy with the leccy 1. I think if you got to stay with the 6mm cable you and need to just swap shower units, try a modern

8kw 1 and we never had a problem with the mira.