I've done a trawl of the archive and I've found some answers, but in
some ways some more questions.

I've a 12 metre plus run to the kitchen sink from the HW tank with
only a 3 - 4 metre head, and have compounded the problem by fitting a
pull out mixer tap which has a high insertion loss. Various solutions
have been played with but a local heat source off the mains seems the
best option.

Just how good are under-sink heaters ? what is the storage types ?
why do they vary in power from 2.2 to 9.5Kw? What is the problem with
expansion - I would have just a short pipe run to the mixer tap ?
Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Any help would be appreciated guys, many thanks.

Rob

On 3 May 2004 15:21:20 -0700, (Rob Graham)
wrote:

I've done a trawl of the archive and I've found some answers, but in
some ways some more questions.

I've a 12 metre plus run to the kitchen sink from the HW tank with
only a 3 - 4 metre head, and have compounded the problem by fitting a
pull out mixer tap which has a high insertion loss. Various solutions
have been played with but a local heat source off the mains seems the
best option.

Just how good are under-sink heaters ? what is the storage types ?
why do they vary in power from 2.2 to 9.5Kw? What is the problem with
expansion - I would have just a short pipe run to the mixer tap ?
Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Any help would be appreciated guys, many thanks.

Rob

Undersink heaters come in two power ranges. 2-3kW with storage which
will deliver a reasonable volume of water to fill a sink, wash hands
etc. They will do this at good flow rate, but once the store is
empty that's it. They can be run from a spur on the ring circuit.

The 8-10kW models are "instantaneous". They deliver water at a
reasonable rate although very slowly in the winter. They need a
special circuit delivering about 45A to the heater - rather like one
of the pathetic electric showers.

Certain types of heater are OK with a standard tap, others need a
special tap or have installation rules.




..andy

To email, substitute .nospam with .gl

In article ,
(Rob Graham) writes:
I've done a trawl of the archive and I've found some answers, but in
some ways some more questions.

I've a 12 metre plus run to the kitchen sink from the HW tank with
only a 3 - 4 metre head, and have compounded the problem by fitting a
pull out mixer tap which has a high insertion loss. Various solutions
have been played with but a local heat source off the mains seems the
best option.

Just how good are under-sink heaters ? what is the storage types ?
why do they vary in power from 2.2 to 9.5Kw?

The low power ones heat up a small tank of water -- if you won't be
running off more than this amount more frequently than the reheat
period, these can be good, but I doubt that would apply at most
kitchen sinks. They are hot all the time and lose heat -- in
sci.engr.electrical someone recently worked out the heat loss was
equivalent to burning a 60W lamp continuously IIRC (although this
was a US one and UK ones may be better insulated).

The higher power ones heat the water on demand -- they are very
similar to electric showers. The hot water supply is unlimited, but
the flow rate will be more limited at higher temperatures. They
will require a heafty mains cable and high current fuseway.

What is the problem with
expansion - I would have just a short pipe run to the mixer tap ?

When the water is heated it expands and forces a small amount of
water back into the water main. This is permitted only to a limited
extent.

Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Vented taps look like a regular singular tap, but the tap knob
actually controls flow in a separate pipe from the one feeding the
tap, which is always 'on'. They work by cutting off the input to the
storage tank and leave the output permanently 'on' (vented). As the
water expands in the heater, the excess drips from the tap. People
try to stop this dripping by turning off the tap harder, and IME the
washer is quickly destroyed and the tap really does start to leak.
Also there's a sort of 5 second delayed action when the tap is opened
or closed. This is not how people expect a tap to behave and also
causes people to turn it off harder, knackering it. I don't see how
this could be used with a mixer.

--
Andrew Gabriel

What is the problem with expansion - I would have just a short pipe run to
the
mixer tap ?

There's also the stored water to expand too.

Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Vented taps won't help you. You need to get a storage type heater with
enough storage to do what you need. It will probably have a 3kW element or
thereabouts. You need to get the type with a built in expansion vessel. This
will contain the pressure increase as the water is heated without requiring
vented taps or long pipe runs.

Christian.

storage tank and leave the output permanently 'on' (vented). As the
water expands in the heater, the excess drips from the tap. People
try to stop this dripping by turning off the tap harder, and IME the
washer is quickly destroyed and the tap really does start to leak.
Also there's a sort of 5 second delayed action when the tap is opened
or closed. This is not how people expect a tap to behave and also
causes people to turn it off harder, knackering it. I don't see how
this could be used with a mixer.

--
Andrew Gabriel

Any hints on how to change the washer on a vented tap - replacements are
£100... and I cannot see how to take the existing tap apart. Would it be
better to fit a pressure release valve, discharging outside, and then fit an
ordinary tap.

Peter

"Christian McArdle" wrote in message .net...
What is the problem with expansion - I would have just a short pipe run to
the
mixer tap ?

There's also the stored water to expand too.

Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Vented taps won't help you. You need to get a storage type heater with
enough storage to do what you need. It will probably have a 3kW element or
thereabouts. You need to get the type with a built in expansion vessel. This
will contain the pressure increase as the water is heated without requiring
vented taps or long pipe runs.

Christian.


Thanks guys - that probably answers enough questions for the moment
for me to proceed, or think about.

Rob

(Rob Graham) wrote in message . com...
I've done a trawl of the archive and I've found some answers, but in
some ways some more questions.

I've a 12 metre plus run to the kitchen sink from the HW tank with
only a 3 - 4 metre head, and have compounded the problem by fitting a
pull out mixer tap which has a high insertion loss. Various solutions
have been played with but a local heat source off the mains seems the
best option.

Just how good are under-sink heaters ? what is the storage types ?
why do they vary in power from 2.2 to 9.5Kw? What is the problem with
expansion - I would have just a short pipe run to the mixer tap ?
Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Any help would be appreciated guys, many thanks.

Rob

Here's some more answers to my own questions -

http://www.heatraesadia.com/hs/heatraes.nsf

if you go to the 'accessory packs', ther is a link there to
installation diagrams which are very useful.

Rob

On 3 May 2004 15:21:20 -0700, (Rob Graham)
wrote:

I've done a trawl of the archive and I've found some answers, but in
some ways some more questions.

I've a 12 metre plus run to the kitchen sink from the HW tank with
only a 3 - 4 metre head, and have compounded the problem by fitting a
pull out mixer tap which has a high insertion loss. Various solutions
have been played with but a local heat source off the mains seems the
best option.

Just how good are under-sink heaters ? what is the storage types ?
why do they vary in power from 2.2 to 9.5Kw? What is the problem with
expansion - I would have just a short pipe run to the mixer tap ?
Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Hi,

I've got one of the £90 screwfix ones, has it has 10L capacity and a
1.2kW element, comes with separate pressure release valve and is
suitable for mains pressures.

This will take about 20 minutes to heat up to 60°C from room
temperature, and I would guess about 40W/h to keep it there.

Since the pipe to the boiler contains only about 2L of water if you're
using 15mm, there is not much to worry about running out of hot water.

Another option could be to use heating tape along the pipe, this would
take about 70W/h to keep the pipe at 60°C if the pipe has 1/2 inch of
insulation.

The electricity used by both of the above would be reduced by putting
them on a time switch, adding more insulation is also a help.

cheers,
Pete.

Pete C wrote in message . ..
On 3 May 2004 15:21:20 -0700, (Rob Graham)
wrote:

I've done a trawl of the archive and I've found some answers, but in
some ways some more questions.

I've a 12 metre plus run to the kitchen sink from the HW tank with
only a 3 - 4 metre head, and have compounded the problem by fitting a
pull out mixer tap which has a high insertion loss. Various solutions
have been played with but a local heat source off the mains seems the
best option.

Just how good are under-sink heaters ? what is the storage types ?
why do they vary in power from 2.2 to 9.5Kw? What is the problem with
expansion - I would have just a short pipe run to the mixer tap ?
Would I be best to arrange a longer run ? I've seen something about
vented taps - how do these things fit in with an ordinary mixer?

Hi,

I've got one of the £90 screwfix ones, has it has 10L capacity and a
1.2kW element, comes with separate pressure release valve and is
suitable for mains pressures.

This will take about 20 minutes to heat up to 60°C from room
temperature, and I would guess about 40W/h to keep it there.

Since the pipe to the boiler contains only about 2L of water if you're
using 15mm, there is not much to worry about running out of hot water.

Another option could be to use heating tape along the pipe, this would
take about 70W/h to keep the pipe at 60°C if the pipe has 1/2 inch of
insulation.

The electricity used by both of the above would be reduced by putting
them on a time switch, adding more insulation is also a help.

cheers,
Pete.

Thanks Pete - that's quite useful. Ref. the pressure release valve -
does that avoid the use of an expansion vessel if there is inadequate
run to the hot tap. Althought there is a long run from my HW tank,
the mains feed runs passed the kitchen sink, so I was thinking if
fitting the heater quite close by. It seems that such an expansion
vessel is required if the pipe length to the tap is short (that at
least is what the Sadia web page says - see the link in an earlier
posting)

Rob

In article ,
"Peter" writes:

storage tank and leave the output permanently 'on' (vented). As the
water expands in the heater, the excess drips from the tap. People
try to stop this dripping by turning off the tap harder, and IME the
washer is quickly destroyed and the tap really does start to leak.
Also there's a sort of 5 second delayed action when the tap is opened
or closed. This is not how people expect a tap to behave and also
causes people to turn it off harder, knackering it. I don't see how
this could be used with a mixer.

Any hints on how to change the washer on a vented tap - replacements are
£100... and I cannot see how to take the existing tap apart. Would it be

No idea. I notice the maintenance people at work just gave up on trying
to keep the vented tap working, and have replaced the whole heater with
one which mounts on the wall, with a regular tap on the input.

better to fit a pressure release valve, discharging outside, and then fit an
ordinary tap.

That won't work -- the tank is not designed for mains water pressure.
(It probably does already have a pressure release valve.)

--
Andrew Gabriel

On 6 May 2004 14:18:31 -0700, (Rob Graham)
wrote:


Thanks Pete - that's quite useful. Ref. the pressure release valve -
does that avoid the use of an expansion vessel if there is inadequate
run to the hot tap. Althought there is a long run from my HW tank,
the mains feed runs passed the kitchen sink, so I was thinking if
fitting the heater quite close by. It seems that such an expansion
vessel is required if the pipe length to the tap is short (that at
least is what the Sadia web page says - see the link in an earlier
posting)

Hi,

The distributors say in their info that they are suitable for use
without an expansion vessel, where the inlet water pressure does not
exceed 6bar/88psi, and the expanded water can be accommodated by the
pipework.

They then specify in turn that there should be a minimum of 9' of
pipework for the 10L model between the inlet and any non return valve
on the supply, to accomodate expanded water.

The pressure release valve is meant as a safety valve and must be
installed into a tee on the cold water supply pipework. The one I had
supplied is 6 bar and with 2 1/2" BSP female connections, one as an
overflow.

It's pretty easy to install, it comes with a mounting plate it slots
onto. The connections can do with some boss white or similar goo as
PTFE tape doesn't quite cut it.

I bought it from Screwfix but it's distributed by Harlequin Products,
contact details as follows:

http://www.applegate.co.uk/engineering/company/co_1177040.htm

cheers,
Pete.