Under sink water heater - tank or no tank?

I'm thinking of getting some under sink water heaters at work, I was going to fit a boiler but thinking that as we use hot water merely for hand washing, rinsing cups etc these could be more cost effective than having the boiler running while the hot water eventually materialises. (Opinions on that would be appreciated though, given the cost difference between gas/electric)
Then if going for the under sink units, would gut instinct lead one to get ones with or without a tank (thinking 10/15l)?
Cheers.
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On Monday, 24 September 2018 12:51:32 UTC+1, R D S wrote:

You will need a tank.
Instantaneous ones are okay for handwashing in toilets but for anything more than a lukewarm dribble you will either need 7kW+ and dedicated wiring, or a tank.
Being unvented they need a pressure relief valve and discharge pipe, and in most cases a pressure vessel too. The over-sink vented ones are easier to install, but because the outlet tap is vented they drip.
Owain
Owain
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On 24/09/2018 13:55, snipped-for-privacy@gowanhill.com wrote:

They used to be called Sadia Heaters. Mostly over sink, with a long spout you swung across the sink, which, as you indicated, dripped as it was heating up.
I was in a place which had an under sink heater which worked the same way: the hot water tap looked like a conventional tap but the knob worked a long rod that controlled the inlet to the heater in the same way as the over sink kind.
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Max Demian

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Sadia was simply one make.
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from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
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There's also a version that uses a mixer tap with three ports: cold water in, cold water out to the heater, and hot water back from the heater.
Example: https://www.tlc-direct.co.uk/Products/HHHF05MVC.html
Advantages: very simple installation, not too pricey
Disadvantages: single tap only, dribble from the tap as the water heats up
Steve
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On 24/09/2018 12:51, R D S wrote:

If you want a sinkfull of water at a time, get one with a tank as long as there is space. If you really only need a dribble for hands or cups one at a time, an instantaneous should be fine. There are also over sink heaters of both types, they take up some space but are easier to fit.
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On 24/09/2018 12:51, R D S wrote:

I would probably go for undersink unvented. The smaller ones have less difficult control requirements than the full size ones.
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Cheers,

John.
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On 24/09/2018 12:51, R D S wrote:

How much do you want to spend? We've got a Quooker under-sink boiling water heater in our kitchen, which is very good - but expensive.
This holds 7 litres of boiling water in an insulated container. It has a boiling water tap - which can be used for making tea or coffee without needing a kettle. It also has a mixing valve to feed mixed boiling/cold water (in other words *hot* water) to the sink's hot water tap for hand washing and washing up.
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Roger
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On 24/09/2018 12:51, R D S wrote:

Provided that you can educate people not to turn the tap on and walk away until it runs hot then the 10/15L under counter hot water heater will be fine. You have to provide an escape for over pressure and meet certain mains water pressure requirements which may require an expansion chamber and pipework to an external overflow/steam vent.
We have them in our village hall. They are fine in toilets but less good in a position where a lot of washing up might be done in a short space of time. I regret not having a 7kW flash boiler type fitted on their downstairs kitchen sink (it is about 3m from the main fusebox).
Worth putting them on timeswitches - as they do consume a bit too much power for my liking on standby full of ready to use hot water.
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Regards,
Martin Brown
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On Monday, September 24, 2018 at 12:51:32 PM UTC+1, R D S wrote:

The heaters with tanks are very expensive and store hot water which is a wa ste if you don't need it all the time. I have an instant under counter wate r boiler running off cold mains water so the water is very hot in summer an d warm in winter which is no hardship. You can get them on ebay made in Eas tern Europe for about £55 and work on a ring main so no special wiring (ie cooker /shower cable) up to 5.5 kw but do check with an electrician. Y ou will need a vented tap though. https://www.ebay.co.uk/itm/5-5KW-DAFI-INLINE-UNDER-SINK-WATER-HEATER-TANKLE SS-ELECTRIC-BOILER-HOT-WATER/323405298814?epid12716898&hash=item4b4c 753c7e:g:NdgAAOSwKsZben2B
My advice is go for the over counter dripping variety.
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On Tuesday, 25 September 2018 12:13:21 UTC+1, alanjones wrote:

Anything above 3kW MUST go on a suitable radial circuit
Some would say 2kW.
Owain
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On 25/09/2018 12:13, alanjones wrote:

They start at around £80

If they are well insulated, that should be less of a worry. However it will depend a bit on how often the hot water is required.

A 5.5kW load is *not* suitable for connecting to a general purpose socket circuit.
It needs a dedicated circuit. That *could* be a ring if you wanted, but there would be no advantage in it being so.
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John.
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