Boiling water

[JohnW2]

Franke 4-in-1 Omni....

Thanks. but that's relatively low-powered (1.5kW) and not an 'instantaneous' heater, since it appears to store hot water (presumably under a little pressure, since it's stored at 105°C, with a 'heating up time' of 20 mins).

Kind Regards, John

 

[JohnW2]

The suppliers seem rather shy to state the power, just that they cost less than 3p per day, and run from a 13A plug!

Well, the plug sets an upper bound for the power! I think that there are plenty of 3kW kettles around (although I think most are about 2kW), so, given the laws of physics as they are, the 'instantaneous' water heater (of 3kW max) did not ought to be able to 'beat' (in terms of speed) such a kettle!

Kind Regards, John

 

[JohnW2]

Kettle may boil quicker but how much would it cost? Gas is cheaper.

It is. However, in terms of the big picture, I would think that the cost difference of boiling a pint or two of water with gas or electricity would be pretty trivial. Were we talking about wanting a bath full of hot water, that would be a different matter.

Kind Regards, John

 

[ericmark]

I presume that we're not trying to re-write the Laws of physics, so I wonder what power these 'instantaneous' heaters are?

Kind Regards, John

The one we have is 3 kW clearly, not instant but faster than a kettle. To make a cup of coffee great, but to make multiple cups of coffee it actually means instead of putting kettle on preparing the cups then come back 5 minutes latter to pour, one ends up hovering over the thing, swapping cups and topping it up. I have tried to convince my wife we need to change how we do things to suit the new boiler, and use it like we did with a coffee filter machine, and help our selves as and when we fancy a cup of coffee.

However she seems to have got it into her head that it's my job to make coffee. Which does not work when it boils one cup at a time.

As to insulating kettles and pans, why not? In the old days with a gas flame or very hot hob I can see why the pan is in insulated as it would likely burn. We have insulated kettles

Thermos Electric Kettle V1 - 1.5L White
This is not only an Electric Kettle! Boil water, serve and keep it hot with the HubimexTM Thermal Electric Kettle. Leak proof stopper ensures no spills, and double wall stainless steel construction with vacuum insulation improves thermal retention to keep your water hot for hours. Just click to boil the water. Serve directly from the Kettle with its comfortable, no-drip spout, or pour a cupful into the drinking cup while keeping the rest of your water hot for later. A cool touch body, ergonomic handle and non-spill lid give you a secure mind when on the go.

So why not insulated pans, or at least tea cosy type covers to keep pans warm?

 

[rsgaz]

not an 'instantaneous' heater, since it appears to store hot water

Isn't that how they all work, otherwise, like you say, it'd need to be WAY over 3kW?

a 'heating up time' of 20 mins

From initial power on, not relevant to someone who keeps it on continuously, maybe useful info if you intend to switch if off overnight or add a timer, say.

I think the 'recovery time' of 10 mins is more meaningful. I would assume that means if you have used all 4 litres in the tank. Residual heat of the tank itself plus 1.5kW to boil 4 litres sounds about right.

 

[EFLImpudence]

I think "instantaneous" is (mis)used in the sense that the hot water is "always instantly" available.


That is they are just kettles under the sink in which the water is maintained at the temperature.

 

[stillp]

Isn't that how they all work, otherwise, like you say, it'd need to be WAY over 3kW?

Aren't there some that heat the water as it flows through, like a Nespresso machine? (Or aan electric shower).

 

[JohnW2]

Isn't that how they all work, otherwise, like you say, it'd need to be WAY over 3kW?

I didn't think so - I thought (but may be wrong) that some were real-time 'instantaneous' heaters (like a shower, but presumably with much slower flow rates) - and hence, as you say, presumably appreciably more than 3kW. The moment one starts storing water at near boiling temp, the whole concept changes, and the cost-efficiency likely to take a dive (at least in a domestic environment).

I think the 'recovery time' of 10 mins is more meaningful. I would assume that means if you have used all 4 litres in the tank. Residual heat of the tank itself plus 1.5kW to boil 4 litres sounds about right.

Maybe. I was not really sure what they meant by 'recovery time'.

Kind Regards, John

 

[JohnW2]

I think "instantaneous" is (mis)used in the sense that the hot water is "always instantly" available. That is they are just kettles under the sink in which the water is maintained at the temperature.

Maybe (in the same sense that stored DHW is more-or-less 'instantly available') - but, as I've just written, I thought that at least some were truly 'instantaneous' (like a shower).

Continuously storing (and presumably having to 'top up the heat') water at near boiling temp must surely be a daft idea in a domestic environment?

Kind Regards, John

 

[stillp]

Isn't that how they all work, otherwise, like you say, it'd need to be WAY over 3kW?

Depends on the flow rate.

 

[rsgaz]

some that heat the water as it flows through, like a Nespresso machine?

some were real-time 'instantaneous' heaters (like a shower, but presumably with much slower flow rates)

Yeah, but those machines also have a warm-up time, then they dribble boiling water through the capsule thingy into a very small coffee mug!!

Just as an example, a small cafe style machine I found is 4.5kW and even then it has a 5 litre tank on-board to keep at near boiling temperature, so you still couldn't call it a 'real time boiling tap'!

 

[ban-all-sheds]

View attachment 127643

So it can't replace a kettle for all uses (stale water).

Unless it has almost zero losses, it must cost more than a kettle to run.

It would appear to contravene requirement G3(3) of the Building Regulations.

 

[ban-all-sheds]

The one we have is 3 kW clearly, not instant but faster than a kettle.

Faster than a 3kW kettle?

 

[rsgaz]

Depends on the flow rate.

Indeed, lets take a very conservative rate 'normal' tap which takes 10 seconds to fill a litre jug...

4.184 Joules * 100 ml * (100-15) degrees = 35564 Joules per second.

In other words, a 'proper' continuous instant boiling tap would need to be 35.5kW !!!

 

[JohnW2]

Just as an example, a small cafe style ... and even then it has a 5 litre tank on-board to keep at near boiling temperature, so you still couldn't call it a 'real time boiling tap'!

Yes, but there's the problem. If the boiling water is in constant demand (as in a coffee shop or cafe etc.), then whether or not it stores water at near-boiling temperature is really neither here nor there, since it has to be powerful enough to boil more water as fast as it is being used (i.e. close to 'real time boiling').

The domestic situation is obviously totally different, since demand is very infrequent - but that is the same reason why it makes little sense to continuously maintain a 'tank' of water at near boiling temperature in a domestic environment.

Kind Regards, John