ISTR some one cleverer than me, not hard, recently laying out the maths of energy required to heat water. Could someone point me in the direction of that post please.

I'm curious to debunk some astounding claims being made about them.

I'm referring to the type that heat the water as it flows. Not the type with a water tank.

Many thanks

On 16/03/15 17:21, fred wrote:
ISTR some one cleverer than me, not hard, recently laying out the maths of energy required to heat water. Could someone point me in the direction of that post please.

I'm curious to debunk some astounding claims being made about them.

I'm referring to the type that heat the water as it flows. Not the type with a water tank.

Many thanks


The physics is invariant - it costs exactly the same to heat 1kg of
water through (say) 90K.

The only argument for instantaneous heaters is they only heat what is
needed (plus a little in the block). OTOH they are rather more expensive
than a kettle, which can also heat small amounts.

On 16/03/2015 17:21, fred wrote:

ISTR some one cleverer than me, not hard, recently laying out the maths of energy required to heat water.
Could someone point me in the direction of that post please.

I'm curious to debunk some astounding claims being made about them.

I'm referring to the type that heat the water as it flows. Not the type with a water tank.

Basically they are just about as efficient as you can ever hope to make
it with just a small volume of water flash heated to the required
working temperature as and when needed. Entropy says this is *the* way
to do it. Pushing heat into already hot bulk water is harder.

The clever ones even wrap the incoming cold water around the heater so
that essentially no heat is wasted by escaping to the outside apart from
the thermal interia of the hardware itself.

The only thing is they need an insane current supply to do it and they
are more complex and perhaps inclined to go wrong if you are unlucky.

Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated. Snag is when someone comes
along and opens the tap full bore waiting for it to run hot.

--
Regards,
Martin Brown

On 16/03/2015 18:08, Tim Watts wrote:
On 16/03/15 17:21, fred wrote:
ISTR some one cleverer than me, not hard, recently laying out the
maths of energy required to heat water. Could someone point me in the
direction of that post please.

I'm curious to debunk some astounding claims being made about them.

I'm referring to the type that heat the water as it flows. Not the
type with a water tank.

Many thanks


The physics is invariant - it costs exactly the same to heat 1kg of
water through (say) 90K.

Although that is true it also costs money to keep bulk ho****er at a
high temperature on the off chance that some of it might be used.

The only argument for instantaneous heaters is they only heat what is
needed (plus a little in the block). OTOH they are rather more expensive
than a kettle, which can also heat small amounts.


--
Regards,
Martin Brown

Tim Watts wrote:

The only argument for instantaneous heaters is they only heat what is
needed (plus a little in the block).

Provided that you have soft water. The life is very short otherwise.

Martin Brown wrote:
Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated.

The problem with using them for drinks is that you have to run off the
cold water, then fill the cup to heat it, then throw the water away and
refill the cup. It's very inefficient compared to a kettle with the
right amount of water in it. Must be soft water.

Going off, or maybe veering off at a tangent, has anyone had any experience of insulated kettles like (random googling)
vektra.co.uk
???

These would seem to be a good compromise between the complexity and expense of the sink heater and the frightening inefficiency of the kettle (especially when the latter is used to heat 1.5 l of water for two mugs of tea...

David

David wrote:
Going off, or maybe veering off at a tangent, has anyone had any experience of insulated kettles like (random googling)
vektra.co.uk
???

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled."

You have to laugh, don't you.

--
Mike Barnes
Cheshire, England

Capitol posted
Martin Brown wrote:
Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated.

The problem with using them for drinks is that you have to run
off the cold water, then fill the cup to heat it, then throw the water
away and refill the cup. It's very inefficient compared to a kettle
with the right amount of water in it. Must be soft water.

I am thinking about getting one, not for drinks but for washing up. Our
kitchen sink is so far from the HW tank that it takes several minutes to
get hot water. One of these devices installed under the sink might stop
my wife complaining. We have very soft water, and anyway it would only
need to be hand hot, say 45 degC.

--
Les

"fred" wrote in message
...
ISTR some one cleverer than me, not hard, recently laying out the maths of
energy required to heat water. Could someone point me in the direction of
that post please.

I'm curious to debunk some astounding claims being made about them.

I'm referring to the type that heat the water as it flows. Not the type
with a water tank.

Many thanks

You eliminate the heat losses /standing losses from the storage tank.
Depending on how much hot water you use and if you use the water immediately
or not.
If you leave this type o fheater permenently on, you will waste a lot of
energy.
Especialy if your hot water needs are low.

I have this type but I use the water immediately it is hot and
(main reason for having them) I use them from my solar PVpanels so water is
available in the evening.

Also the hot water pipe run is short, this savesenergy too.

Instant heaters need a big electricity supply or they only heat the water
fast enough to provide a miserable dribble.
So, commonly used for spray taps for hand washing.
But very little heat losses.

On 16/03/15 20:54, Capitol wrote:
Martin Brown wrote:
Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated.

The problem with using them for drinks is that you have to run off
the cold water, then fill the cup to heat it, then throw the water away
and refill the cup. It's very inefficient compared to a kettle with the
right amount of water in it. Must be soft water.

Filling the cup and throwing away would be the same with a kettle

On Monday, March 16, 2015 at 11:26:08 PM UTC, David wrote:

Going off, or maybe veering off at a tangent, has anyone had any experience of insulated kettles like (random googling)
vektra.co.uk
???

These would seem to be a good compromise between the complexity and expense of the sink heater and the frightening inefficiency of the kettle (especially when the latter is used to heat 1.5 l of water for two mugs of tea...

Not sure I see the point of them. Why not just boil the exact amount of water you want? Simply transfer water from tap to kettle via your mug.

A mugful takes 2 minutes at 800w to boil = 1.6kWmins, cost = 13p x 1.6/60 = a third of a penny. To pay back the £65 excess cost would take 3x6500 = 20,000 mugs of water not boiled due to the insulation. So just another greenscam product.


NT

On Tuesday, March 17, 2015 at 8:08:29 AM UTC, wrote:
On Monday, March 16, 2015 at 11:26:08 PM UTC, David wrote:

Going off, or maybe veering off at a tangent, has anyone had any experience of insulated kettles like (random googling)
vektra.co.uk
???

These would seem to be a good compromise between the complexity and expense of the sink heater and the frightening inefficiency of the kettle (especially when the latter is used to heat 1.5 l of water for two mugs of tea....

Not sure I see the point of them. Why not just boil the exact amount of water you want? Simply transfer water from tap to kettle via your mug.

A mugful takes 2 minutes at 800w to boil = 1.6kWmins, cost = 13p x 1.6/60 = a third of a penny. To pay back the £65 excess cost would take 3x6500 = 20,000 mugs of water not boiled due to the insulation. So just another greenscam product.

Or perhaps just another greenscam price. A vacuum flask only costs £3 after all. Adding £3 to kettle cost would only need to avoid 900 cuppas boiled, with a long lived product that may make sense.


NT

Tim Watts wrote:
On 16/03/15 20:54, Capitol wrote:
Martin Brown wrote:
Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated.

The problem with using them for drinks is that you have to run off
the cold water, then fill the cup to heat it, then throw the water away
and refill the cup. It's very inefficient compared to a kettle with the
right amount of water in it. Must be soft water.

Filling the cup and throwing away would be the same with a kettle

The water in the kettle is hotter.

On 17/03/15 10:02, Capitol wrote:
Tim Watts wrote:
On 16/03/15 20:54, Capitol wrote:
Martin Brown wrote:
Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated.

The problem with using them for drinks is that you have to run off
the cold water, then fill the cup to heat it, then throw the water away
and refill the cup. It's very inefficient compared to a kettle with the
right amount of water in it. Must be soft water.

Filling the cup and throwing away would be the same with a kettle

The water in the kettle is hotter.

I thought the in sink ones dispensed near boiling water?

Bit useless for tea otherwise...

On Monday, March 16, 2015 at 6:08:51 PM UTC, Tim Watts wrote:
On 16/03/15 17:21, fred wrote:
ISTR some one cleverer than me, not hard, recently laying out the maths of energy required to heat water. Could someone point me in the direction of that post please.

I'm curious to debunk some astounding claims being made about them.

I'm referring to the type that heat the water as it flows. Not the type with a water tank.

Many thanks


The physics is invariant - it costs exactly the same to heat 1kg of
water through (say) 90K.

The only argument for instantaneous heaters is they only heat what is
needed (plus a little in the block). OTOH they are rather more expensive
than a kettle, which can also heat small amounts.

I fear you've mis-read my post. What I want know is how much energy (electricity) is required to bring cold water, say @ 10 degrees up to 90 degrees as it flows.

Or to put it another what electricity supply would be needed to do this and what flow rate would be achievable with a standard house-hold supply. (Single phase)

My experience of 'Instant' water heaters is that they provide a miserable dribble if you require hot hot water though I think that was from a 13 amp socket.

On 17/03/15 10:23, fred wrote:
On Monday, March 16, 2015 at 6:08:51 PM UTC, Tim Watts wrote:
On 16/03/15 17:21, fred wrote:
ISTR some one cleverer than me, not hard, recently laying out the maths of energy required to heat water. Could someone point me in the direction of that post please.

I'm curious to debunk some astounding claims being made about them.

I'm referring to the type that heat the water as it flows. Not the type with a water tank.

Many thanks


The physics is invariant - it costs exactly the same to heat 1kg of
water through (say) 90K.

The only argument for instantaneous heaters is they only heat what is
needed (plus a little in the block). OTOH they are rather more expensive
than a kettle, which can also heat small amounts.

I fear you've mis-read my post. What I want know is how much energy (electricity) is required to bring cold water, say @ 10 degrees up to 90 degrees as it flows.

What flow rate do you have in mind?

This is the equation - so you can work it out:

Assuming S, specific heat capacity of water is 4200J/kgK,
T is your delta-T (90-10 in your case)
Mass of 1 litre is 1kg - near enough

E is the energy to heat mass m of water through T
F is flow in kg/s which is helpfully more or less l/s too

So

E=mTS

Given a time t

P=E/t
F=m/t

So
P=mTS/t
m=Ft

= P=FtTS/t
= P=FTS

P is in J/s = Watts

and

S=4200J/kgK
So

P=4200x90xF
P=378000F
or, more usefully, converting to kW

P=378F kW

or

F=/378

So a 10kW heater will give you a flow of 0.026kg/s or 1.59kg/min

A 3kW heater will give you: 0.008kg/s or 0.48kg/min = about a pint/min


Does that help?




Or to put it another what electricity supply would be needed to do this and what flow rate would be achievable with a standard house-hold supply. (Single phase)

My experience of 'Instant' water heaters is that they provide a miserable dribble if you require hot hot water though I think that was from a 13 amp socket.

On Tuesday, 17 March 2015 10:23:11 UTC, fred wrote:
Or to put it another what electricity supply would be needed to do this
and what flow rate would be achievable with a standard house-hold supply.
(Single phase)

3 kW / 13 amp will give you a gentle spray of warmish water for hand-washing, not for washing up.

7 kW / 30 amp will give you a weedy-but-adequate shower except in the coldest weather (lowest incoming water temp)

10 kW / 45 amp will give you an adequate shower in almost all conditions.

for comparison the smallest gas combi boiler is usually 24 kW. That will give you a good shower or hot tap flow for washing up (at one tap at a time).

Therefore if you want *hot* water for washing up, you really either need gas, or stored hot water even if it's only a 15 litre unvented heater.

Owain

Tim Watts wrote:
On 17/03/15 10:02, Capitol wrote:
Tim Watts wrote:
On 16/03/15 20:54, Capitol wrote:
Martin Brown wrote:
Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated.

The problem with using them for drinks is that you have to run off
the cold water, then fill the cup to heat it, then throw the water away
and refill the cup. It's very inefficient compared to a kettle with the
right amount of water in it. Must be soft water.

Filling the cup and throwing away would be the same with a kettle

The water in the kettle is hotter.

I thought the in sink ones dispensed near boiling water?

Bit useless for tea otherwise...

They are not hot enough for a tea bag in a cup. Hence the need to
preheat the cup. The reliability is a bit of a problem also, at least
for the some of the US ones.

On 17/03/15 11:24, Capitol wrote:

They are not hot enough for a tea bag in a cup. Hence the need to
preheat the cup. The reliability is a bit of a problem also, at least
for the some of the US ones.

Ok - thanks for explaining that. I assumed they came up to around 100C.

As I said - "bit useless".

In fact worse than useless. Last thing I want is visitors trying to wash
their hands under it - so I rate it as a really dangerous and stupid,
pointless and bollocky invention - a solution without a problem...

SWMBO mentioned it last year prior to us fitting the new kitchen.

I saw that off and explained why. Luckily my SWMBO knows I'm right about
stuff like that and as I do as much domestic stuff as her, I have an
interest in making stuff work too

On 16/03/2015 23:26, David wrote:

Going off, or maybe veering off at a tangent, has anyone had any experience of insulated kettles like (random googling)
vektra.co.uk
???

Not of those ones in particular but such devices are common in Japan
where domestic appliances on 100v cannot support a 3kW kettle so they
have a highly insulated slow kettle that keep water hot.

They are OK but freshly boiled water is still better for making tea.

These would seem to be a good compromise between the complexity and expense of the sink heater and the
frightening inefficiency of the kettle (especially when the latter is
used to heat 1.5 l of water for two mugs of tea...

You can get smaller kettles.

--
Regards,
Martin Brown

Tim Watts wrote:
On 17/03/15 11:24, Capitol wrote:

They are not hot enough for a tea bag in a cup. Hence the need to
preheat the cup. The reliability is a bit of a problem also, at least
for the some of the US ones.

Ok - thanks for explaining that. I assumed they came up to around 100C.

As I said - "bit useless".

In fact worse than useless. Last thing I want is visitors trying to wash
their hands under it - so I rate it as a really dangerous and stupid,
pointless and bollocky invention - a solution without a problem...

SWMBO mentioned it last year prior to us fitting the new kitchen.

I saw that off and explained why. Luckily my SWMBO knows I'm right about
stuff like that and as I do as much domestic stuff as her, I have an
interest in making stuff work too

Yes, I think they are a bit hazardous when you now have 2 hot taps on a
sink. I haven't made the mistake of putting my fingers under the wrong
one just to rinse my hands, yet!

On 17/03/15 07:07, Mike Barnes wrote:
David wrote:
Going off, or maybe veering off at a tangent, has anyone had any
experience of insulated kettles like (random googling)
vektra.co.uk
???

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled."

You have to laugh, don't you.

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled. Testing has shown that after 2
hours the water is at 80°C, hot enough to brew a cup of te... "

******** it is (80C).

Maybe if you are using Tescos Value powdered floor sweepings tea bags.

Proper tea needs proper boiling water...

Tim Watts wrote:
On 17/03/15 07:07, Mike Barnes wrote:
David wrote:
Going off, or maybe veering off at a tangent, has anyone had any
experience of insulated kettles like (random googling)
vektra.co.uk
???

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled."

You have to laugh, don't you.

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled. Testing has shown that after 2
hours the water is at 80°C, hot enough to brew a cup of te... "

******** it is (80C).

Maybe if you are using Tescos Value powdered floor sweepings tea bags.

Proper tea needs proper boiling water...

Some fine Japanese green teas find 80C too hot. Perhaps they're not
"proper tea".

--
Mike Barnes
Cheshire, England

On 17/03/2015 10:07, Tim Watts wrote:
On 17/03/15 10:02, Capitol wrote:
Tim Watts wrote:
On 16/03/15 20:54, Capitol wrote:
Martin Brown wrote:
Even the ones with a small water tank aren't all that bad since the
tanks are typically very well insulated.

The problem with using them for drinks is that you have to run off
the cold water, then fill the cup to heat it, then throw the water away
and refill the cup. It's very inefficient compared to a kettle with the
right amount of water in it. Must be soft water.

Filling the cup and throwing away would be the same with a kettle

The water in the kettle is hotter.

I thought the in sink ones dispensed near boiling water?

Bit useless for tea otherwise...


but what aprice, some in John Lewis are over a grand.

---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com

On 17/03/15 18:25, Mike Barnes wrote:
Tim Watts wrote:
On 17/03/15 07:07, Mike Barnes wrote:
David wrote:
Going off, or maybe veering off at a tangent, has anyone had any
experience of insulated kettles like (random googling)
vektra.co.uk
???

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled."

You have to laugh, don't you.

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled. Testing has shown that after 2
hours the water is at 80°C, hot enough to brew a cup of te... "

******** it is (80C).

Maybe if you are using Tescos Value powdered floor sweepings tea bags.

Proper tea needs proper boiling water...

Some fine Japanese green teas find 80C too hot. Perhaps they're not
"proper tea".


Well I don't drink them, so not really a problem. All the tea in my
house likes 100C or near enough.

How many people in Britain drink fine japanese tea anyway?

Within the context I stand by my original assertion.

Tim Watts wrote:
On 17/03/15 18:25, Mike Barnes wrote:
Tim Watts wrote:
On 17/03/15 07:07, Mike Barnes wrote:
David wrote:
Going off, or maybe veering off at a tangent, has anyone had any
experience of insulated kettles like (random googling)
vektra.co.uk
???

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled."

You have to laugh, don't you.

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled. Testing has shown that after 2
hours the water is at 80°C, hot enough to brew a cup of te... "

******** it is (80C).

Maybe if you are using Tescos Value powdered floor sweepings tea bags.

Proper tea needs proper boiling water...

Some fine Japanese green teas find 80C too hot. Perhaps they're not
"proper tea".


Well I don't drink them, so not really a problem. All the tea in my
house likes 100C or near enough.

How many people in Britain drink fine japanese tea anyway?

Within the context I stand by my original assertion.

Well, as you get to define what "proper tea" is, no one can contradict
you. I wasn't trying to, just widening your horizons a little. FWIW I
just found a packet of Japanese tea in the larder and it says 75-80 degrees.

BTW my amusement with the quote was actually the juxtaposition of
"guarantee" and "up to".

--
Mike Barnes
Cheshire, England

"Capitol" wrote in message
...
Tim Watts wrote:
On 17/03/15 11:24, Capitol wrote:

They are not hot enough for a tea bag in a cup. Hence the need to
preheat the cup. The reliability is a bit of a problem also, at least
for the some of the US ones.

Ok - thanks for explaining that. I assumed they came up to around 100C.

As I said - "bit useless".

In fact worse than useless. Last thing I want is visitors trying to wash
their hands under it - so I rate it as a really dangerous and stupid,
pointless and bollocky invention - a solution without a problem...

SWMBO mentioned it last year prior to us fitting the new kitchen.

I saw that off and explained why. Luckily my SWMBO knows I'm right about
stuff like that and as I do as much domestic stuff as her, I have an
interest in making stuff work too

Yes, I think they are a bit hazardous when you now have 2 hot taps on a
sink. I haven't made the mistake of putting my fingers under the wrong one
just to rinse my hands, yet!



No safety lock?

--
Adam

On 17/03/15 19:10, Mike Barnes wrote:
Tim Watts wrote:

Within the context I stand by my original assertion.

Well, as you get to define what "proper tea" is, no one can contradict
you. I wasn't trying to, just widening your horizons a little. FWIW I
just found a packet of Japanese tea in the larder and it says 75-80
degrees.

BTW my amusement with the quote was actually the juxtaposition of
"guarantee" and "up to".


Fair do's - I'm not really a tea connoisseur anyway, so I tend to brew
up a PG Tips tea bag for visitors at best or a bit of Chinese green (and
whilst opinions vary, it seems to do fine with 100C water) - but I do
love my Nespresso coffee machine - best kitchen invention in decades!

On 17/03/2015 07:07, Mike Barnes wrote:
David wrote:
Going off, or maybe veering off at a tangent, has anyone had any
experience of insulated kettles like (random googling)
vektra.co.uk
???

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled."

You have to laugh, don't you.

But it is true if you define "hot" as "at a higher temperature than
initially". Let alone the "up to".
Its one of those meaningless statements like " powerful enough to heat a
large sitting room" applied to a small "ceramic element" fan heater.

ARW wrote:
"Capitol" wrote in message
...
Tim Watts wrote:
On 17/03/15 11:24, Capitol wrote:

They are not hot enough for a tea bag in a cup. Hence the need to
preheat the cup. The reliability is a bit of a problem also, at least
for the some of the US ones.

Ok - thanks for explaining that. I assumed they came up to around 100C.

As I said - "bit useless".

In fact worse than useless. Last thing I want is visitors trying to wash
their hands under it - so I rate it as a really dangerous and stupid,
pointless and bollocky invention - a solution without a problem...

SWMBO mentioned it last year prior to us fitting the new kitchen.

I saw that off and explained why. Luckily my SWMBO knows I'm right about
stuff like that and as I do as much domestic stuff as her, I have an
interest in making stuff work too

Yes, I think they are a bit hazardous when you now have 2 hot taps on
a sink. I haven't made the mistake of putting my fingers under the
wrong one just to rinse my hands, yet!



No safety lock?


` No, just rapid finger extraction.

Tim Watts wrote:
I do
love my Nespresso coffee machine - best kitchen invention in decades!

Same here. I wish the recycling service wasn't so awkward though.

--
Mike Barnes
Cheshire, England

On Tue, 17 Mar 2015 01:20:46 -0700 (PDT), wrote:

On Tuesday, March 17, 2015 at 8:08:29 AM UTC, wrote:
On Monday, March 16, 2015 at 11:26:08 PM UTC, David wrote:

Going off, or maybe veering off at a tangent, has anyone had any experience of insulated kettles like (random googling)
vektra.co.uk
???

These would seem to be a good compromise between the complexity and expense of the sink heater and the frightening inefficiency of the kettle (especially when the latter is used to heat 1.5 l of water for two mugs of tea...

Not sure I see the point of them. Why not just boil the exact amount of water you want? Simply transfer water from tap to kettle via your mug.

A mugful takes 2 minutes at 800w to boil = 1.6kWmins, cost = 13p x 1.6/60 = a third of a penny. To pay back the £65 excess cost would take 3x6500 = 20,000 mugs of water not boiled due to the insulation. So just another greenscam product.

Or perhaps just another greenscam price. A vacuum flask only costs £3 after all. Adding £3 to kettle cost would only need to avoid 900 cuppas boiled, with a long lived product that may make sense.


Such 'high efficiency measures' often come at such a high cost as to
offer so low a return on investment that in practice they simply
aren't worth implementing except under more extreme and unusual
circumstances of use. The 'highly insulated' electric kettle is just
such a typical example of this type of investment.

I use a 3KW electric jug kettle which can be filled to a minimum of 1
cup's worth (200cc).When boiling up enough water to prewarm the small
stainless steel teapot and fill it to 2 thirds of its 400ml capacity
to brew a mug's worth of tea, I normally fill it to the 2 1/2 cup mark
(about half a litre)[1].

Turning the kettle on with 500ml of slightly warmer than room
temperature water[2] gives me barely enough time to extract and ready
a teabag from the caddy, rinse out my mug from its previous use and
ditto the used teabag and dregs from the teapot and have both ready in
time to lift the boiling kettle from off its base (no pointless
waiting on the boil detection 'stat to switch it off) to pour about a
100ml into the teapot to warm it up and empty into the sink, returning
back to the kettle ready to receive the waiting teabag _after_ turning
the kettle back on for the 4 or 5 seconds it takes me to transfer said
teabag to the pot and let me lift the kettle just as it resumes
boiling (again, no waiting on the boil sensor 'stat to cut out).

[1] The extra 100ml or so is simply the price I'm prepared to pay for
a properly brewed mug of tea. I'm not so uncaring of the quality of a
mug of tea as to penny pinch and brew in the cup.

[2] Once I've filled the teapot to the 2 thirds mark, I then
immediately top the kettle back up to the 2 1/2 cup mark ready for its
next use, not just to save on filling time but to have the water
pre-warmed to a greater or lesser extent compared to cold filling
immediately before its next use thus making productive use of the
current 'brewing time' needed to make a reasonably good 'cup of tea'
and spread the heat energy into a larger lower temperature volume of
water better able to retain its heat over the next hour or so before
its next use.

One might suppose that an insulated kettle would make considerable
savings on the amount of electrical energy consumed sufficient to
justify the additional capital investment involved but the amount of
energy savings involved wouldn't be enough to justify such a
refinement unless you could reasonably expect to see a couple of
decades of service life from such a low margin disposable item as an
electric kettle. TBH, acheiving as much as a decade of use out of a
well chosen electric kettle would be a remarkable feat alone.
--
J B Good

On Tue, 17 Mar 2015 17:40:22 +0000, Tim Watts
wrote:

On 17/03/15 07:07, Mike Barnes wrote:
David wrote:
Going off, or maybe veering off at a tangent, has anyone had any
experience of insulated kettles like (random googling)
vektra.co.uk
???

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled."

You have to laugh, don't you.

"We guarantee that the water in your Vektra kettle will stay hot for up
to 4 hours after it is first boiled. Testing has shown that after 2
hours the water is at 80°C, hot enough to brew a cup of te... "

******** it is (80C).

Maybe if you are using Tescos Value powdered floor sweepings tea bags.

Proper tea needs proper boiling water...

I'm reminded of the spurious claim that the galley tea making hot
water heating units in a 747 Jumbo Jet are precision set to 87 deg C
as the optimal tea brewing temperature when we all know that it's more
to do with the boiling point of water at a cabin pressure
corresponding to an altitude of 10 or 12 thousand feet.

As for the statement, "We guarantee that the water in your Vektra
kettle will stay hot for up to 4 hours after it is first boiled.",
this is totally meaningless without at least two vital statistics
(preferably including a third involving room temperature), the actual
temperature used to define "hot" and the volume of water (eg half
filled or fully filled). The water supply temperature is immaterial in
this case since it only effects how long it'll take to boil the water.
--
J B Good

On Tue, 17 Mar 2015 22:33:48 +0000, Capitol
wrote:

ARW wrote:
"Capitol" wrote in message
...
Tim Watts wrote:
On 17/03/15 11:24, Capitol wrote:

They are not hot enough for a tea bag in a cup. Hence the need to
preheat the cup. The reliability is a bit of a problem also, at least
for the some of the US ones.

Ok - thanks for explaining that. I assumed they came up to around 100C.

As I said - "bit useless".

In fact worse than useless. Last thing I want is visitors trying to wash
their hands under it - so I rate it as a really dangerous and stupid,
pointless and bollocky invention - a solution without a problem...

SWMBO mentioned it last year prior to us fitting the new kitchen.

I saw that off and explained why. Luckily my SWMBO knows I'm right about
stuff like that and as I do as much domestic stuff as her, I have an
interest in making stuff work too

Yes, I think they are a bit hazardous when you now have 2 hot taps on
a sink. I haven't made the mistake of putting my fingers under the
wrong one just to rinse my hands, yet!



No safety lock?


` No, just rapid finger extraction.

And immediate access to a stream of instant cold water. :-)

AFAICR, such 'boiling hot' supplies use a very small spigot, easily
distinguishable from the more usual hot and cold supplies. Also, as
others have pointed out, the initial flow is far from being at 100 deg
C, necessitating some wastage, often usefully used to prewarm the mug
before chucking a teabag or teaspoon of coffee into it.
--
J B Good

Johny B Good wrote:

AFAICR, such 'boiling hot' supplies use a very small spigot, easily
distinguishable from the more usual hot and cold supplies. Also, as
others have pointed out, the initial flow is far from being at 100 deg

I thought some (Quooker?) stored the water above 100°C at mains
pressure, so it instantly boiled as you open the tap and lower the pressure?

Johny B Good wrote:
As for the statement, "We guarantee that the water in your Vektra
kettle will stay hot for up to 4 hours after it is first boiled.",
this is totally meaningless without at least two vital statistics
(preferably including a third involving room temperature), the actual
temperature used to define "hot" and the volume of water (eg half
filled or fully filled).

It's still useless unless you do something about "up to".

--
Mike Barnes
Cheshire, England

On 18/03/2015 18:21, Mike Barnes wrote:
Johny B Good wrote:
As for the statement, "We guarantee that the water in your Vektra
kettle will stay hot for up to 4 hours after it is first boiled.",
this is totally meaningless without at least two vital statistics
(preferably including a third involving room temperature), the actual
temperature used to define "hot" and the volume of water (eg half
filled or fully filled).

It's still useless unless you do something about "up to".

This is a real bugbear of mine. You see the likes of "which" getting
all upset about broadband operators offering "up to X" and then
delivering something less, but in the high street almost every shop has
an "up to 50% off" sale. Good luck trying to find anything that
actually has 50% off.

--
CB

CB wrote:
On 18/03/2015 18:21, Mike Barnes wrote:
Johny B Good wrote:
As for the statement, "We guarantee that the water in your Vektra
kettle will stay hot for up to 4 hours after it is first boiled.",
this is totally meaningless without at least two vital statistics
(preferably including a third involving room temperature), the actual
temperature used to define "hot" and the volume of water (eg half
filled or fully filled).

It's still useless unless you do something about "up to".

This is a real bugbear of mine. You see the likes of "which" getting
all upset about broadband operators offering "up to X" and then
delivering something less,

I remember that _Which_ article: they misleadingly described those "up
to X" come-ons as "promises".

--
Mike Barnes
Cheshire, England

Andy Burns wrote:
Johny B Good wrote:

AFAICR, such 'boiling hot' supplies use a very small spigot, easily
distinguishable from the more usual hot and cold supplies. Also, as
others have pointed out, the initial flow is far from being at 100 deg

I thought some (Quooker?) stored the water above 100°C at mains
pressure, so it instantly boiled as you open the tap and lower the
pressure?


Not aware of those. Seems like a recipe for disaster. Would seem to
depend upon supply pressure available?