Hot tap instalation

kingrobert · 27 Apr 2021

I am installing a new hot tap and its 1600w. Power supply above the work tops I have at the moment is 2x fused 13 amp spur with a 3kw plinth heater and on the other side is a dishwasher both wired straight in to connection plates. Not sure if i would be ok to wire the hot tap tank in to one of these but have a feeling it would be too much load.
Any help would be much appreciated.
TIA

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Jon c · 27 Apr 2021

You are right in thinking there is a possibility of too much load if you connect the tap to either of those FCUs, especially the plinth heater one. If the FCUs are on a ring final circuit (or any other appropriate circuit) you could add another FCU by either spurring off the feed/supply side (preferably from the dishwasher FCU), or extend the ring to the new FCU, which is the better option.

ericmark · 27 Apr 2021

I had a problem in that I wanted to run more from a spur, I used this

the double socket was replaced with a single socket, switch and fuse, I used LAP grid system, you can fit fuses to prevent over load and switches to select between loads, but cable sizes, and MCB sizes are important, I use two one cup water boilers but was careful to ensure not from same socket, so enough time in the adverts to make two cups of coffee, but for that 3 minutes I am using 6 kW so I question how a hot tap can work at 1.6 kW it does seem rather small.

JohnW2 · 27 Apr 2021

ericmark said:
... I question how a hot tap can work at 1.6 kW it does seem rather small.

Agreed. I can't see how 1.6 kW could provide 'instant hot water heater ('on demand') at a sensible/usable flow rate. Accordingly, I think that some of these ('low powered') so-called 'hot taps' actually store hot water - which makes them pretty inefficient/cost-ineffective.

Kind Regards, John

BS3036 · 27 Apr 2021

Looking up taps of that wattage produced:
However the Nordic Combi square tap eliminates this issue as it will provide instant hot (50-60°C) and boiling water (100°C) all from a single tank tucked neatly under the kitchen sink.

JohnW2 · 27 Apr 2021

BS3036 said:
Looking up taps of that wattage produced: However the Nordic Combi square tap eliminates this issue as it will provide instant hot (50-60°C) and boiling water (100°C) all from a single tank tucked neatly under the kitchen sink.

Quite so!

Kind Regards, John

kingrobert · 27 Apr 2021

Thanks for your replies. It is a Quooker hot tap apparently the best on the market. It has a 3ltr storage tank and claims to have daily running cost of 3p per day on standby.

JohnW2 · 27 Apr 2021

kingrobert said:
Thanks for your replies. It is a Quooker hot tap apparently the best on the market. It has a 3ltr storage tank and claims to have daily running cost of 3p per day on standby.

That's probably not too far off.

The manual says that it stores water at 110°C (which presumably implies that it must be stored 'under pressure'). If one assumes incoming cold water temp is about 18°C then, by my calculations, to raise 3 litres of water from 18°C to 110°C would require about 0.32 kWh of electricity - which at, say, 16p per kWh would cost about 5.2p. How much electricity (hence cost) it would take to keep the water at that temperature for 24hours obviously depends entirely on how well lagged the tank is, but I obviously don't have a clue about that. The manual claims a 'standby' power requirement of 10W (presumably an 'average') which, if true, would cost around 3.8p per day (at 16p/kWh).

The 'heat up time' of 10 minutes they quote also sounds about right - the 0.32 kWh I have estimated above should, with a 1,600W heater, take about 12 minutes.

Kind Regards, John

RF Lighting · 27 Apr 2021

We have one of these taps in the kitchen of the office I’m currently based in. It’s quite a scary beast as the steam pressure really blasts the water out!

JohnW2 · 27 Apr 2021

RF Lighting said:
We have one of these taps in the kitchen of the office I’m currently based in. It’s quite a scary beast as the steam pressure really blasts the water out!

Yes, I've met (and also been frightened by!) such animals myself.

I haven't done the sums, but to keep water liquid at 110°C probably requires quite a significant pressure - so, basically, one has a 'pressure cooker' sitting under one's sink, and releases the 'pressure valve' when one turns a tap on!

Kind Regards, John

AdrianUK · 27 Apr 2021

JohnW2 said:
I haven't done the sums, but to keep water liquid at 110°C probably requires quite a significant pressure

Perhaps not as much as you might think... "steam tables" will reveal the answer to be around 1.4bar absolute, so 0.4 bar about atmos or around 6psi.

JohnD · 28 Apr 2021

JohnW2 said:
Agreed. I can't see how 1.6 kW could provide 'instant hot water heater ('on demand') at a sensible/usable flow rate. Accordingly, I think that some of these ('low powered') so-called 'hot taps' actually store hot water - which makes them pretty inefficient/cost-ineffective.

Kind Regards, John

It's only intended to fill a teapot.

Not to give sustained flow.

JohnW2 · 28 Apr 2021

JohnD said:
It's only intended to fill a teapot. Not to give sustained flow.

If one was doing on-demand heating, one would have to be quite patient waiting for the flow (whether you called it 'sustained' or not) to fill a tea-pot (about 4 minutes per litre, per my calcs above).

However, we now know the actual situation - and I'm not convinced that keeping 3 litres of water at 110°C for 24/7 is necessarily the wisest approach if one's desire is to (very occasionally, I presume) 'fill a teapot'!

Kind Regards, John

JohnW2 · 28 Apr 2021

AdrianUK said:
Perhaps not as much as you might think... "steam tables" will reveal the answer to be around 1.4bar absolute, so 0.4 bar about atmos or around 6psi.

As I said, I hadn't done the sums (or looked it up) - but I think you'll find that 40% above atmospheric pressure is enough to produce a pretty big 'whoosh' if one suddenly 'lets it loose' on the atmosphere

If I recall correctly (maybe not

), traditional UK piped gas supplies are around 20-25 mbar (above atmospheric), and that can certainly 'whoosh out' if one opens a tap - with what (f I'm correct) is only about one-twentieth of the steam pressure you're talking about.

Kind Regards, John

EFLImpudence · 28 Apr 2021

Won't it be more than merely the 6psi pressure being 'allowed out' as the water will then boil and steam be formed?

Look at taking off a car radiator cap when the engine is hot, albeit that is (usually) 13psi.

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