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
Then if going for the under sink units, would gut instinct lead one to
get ones with or without a tank (thinking 10/15l)?
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.
On 24/09/2018 13:55, firstname.lastname@example.org 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.
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
Advantages: very simple installation, not too pricey
Disadvantages: single tap only, dribble from the tap as the water
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.
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.
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.
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.
My advice is go for the over counter dripping variety.
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