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  #1   Report Post  
Mike Hibbert
 
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Default Why is this a bad idea?

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a feed
fron the hot and cold water supply going into one pipe and then feeding the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike


  #2   Report Post  
MrCheerful
 
Posts: n/a
Default Why is this a bad idea?

Mike Hibbert wrote:
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one
else suggest it. I'm looking at shower options at the moment, and I
live in an area with fairly low water pressure. One of the easiest
options would be to have an electric shower, but I have hear that

the
water pressure would be even worse in winter as the shower would

need
to heat the water from a lover ambient temperature.

So, why not mix the water with hot water from the combi? I could

have
a feed fron the hot and cold water supply going into one pipe and
then feeding the electric shower. The water would be pre-warmed and
therefore could be made the same all year round. If the electric
shower wasn't raising the temperature too much it woudn't have such

a
problem delivering more water would it?

Like I say, this is based purely on my own "sort of" logic rather
than any fact, so shoot me down gently!

Cheers
Mike


There is no reason you couldn't feed the hot and cold into a
thermostatic mixer and then into an electric shower. I wanted some
more pressure for my shower so ran a large feed from the cold tank
(yes I know you haven't got one, but you could add one) into a pump
and then into a high power shower unit, this works fine and you can't
get scalded by someone flushing the loo.

MrCheerful


  #3   Report Post  
Roger Mills
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike


I don't profess to be an expert on combis - but surely, if you connect the
output of the combi to a cold supply at mains pressure, you won't have any
flow through the combi - because the input and output will be at the same
pressure.

If the combi delivers an adequate supply of hot water, all you need is a
shower mixing valve to blend hot and cold - rather than an electric shower.

Roger


  #4   Report Post  
Andy Hall
 
Posts: n/a
Default Why is this a bad idea?

On Wed, 27 Aug 2003 20:11:32 GMT, "Mike Hibbert"
wrote:

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a feed
fron the hot and cold water supply going into one pipe and then feeding the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike


I'm not sure that it's going to help you.

Electric showers are normally rated at up to about 10kW and the
pipework and shower head designed to give a fairly low flow rate.
This is because 10kW is a relatively small about of heat to add to
water to raise it from cold water mains temperature to the normal
working temperature of around 40 degrees.

You can actually do the sums. Let's say the water is at 10 degrees
coming in. You need to raise the temperature by 30 degrees, so using
Heat energy = mass x specific heat x temperature rise, we have

10000 = M x 4200 x 30

since the specific heat of water is 4200 Joules/kg

A litre of water weighs approx. 1kg so you can work out that this
amount of energy will be enough to heat approx. 0.08 litres per second
or about 4.75 litres/minute.

This equates to a disappointing shower.

A typical combi may have a power rating of 20-30 (possibly even as
much as 45kW), so under the same circumstances of needing to raise the
water temperature by 30 degrees will give you 2 to 4.5 times the flow
rate, which becomes a lot more sensible.

However, if the issue is that the water pressure, or more importantly
the flow rate is poor, then adding in more heating of the water is not
going to help.

If the issue were that the combi is under-rated and water supply is
adequate, then theoretically, adding in another source of heat would
be interesting. However, I am not sure that water regulations or the
manufacturers of electric showers would make this a feasible option.

With a flow rate issue because of the water supply, the options would
be to upgrade the water supply pipe from the street main (you would
have to pay for this unless the supply rate is *extremely* low, or to
have some form of cold water storage tank and a shower pump.


..andy

To email, substitute .nospam with .gl
  #5   Report Post  
Mike Hibbert
 
Posts: n/a
Default Why is this a bad idea?

"Roger Mills" wrote in message
...

"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in

an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would

be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be

made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more

water
would it?

Like I say, this is based purely on my own "sort of" logic rather than

any
fact, so shoot me down gently!

Cheers
Mike


I don't profess to be an expert on combis - but surely, if you connect the
output of the combi to a cold supply at mains pressure, you won't have any
flow through the combi - because the input and output will be at the same
pressure.

If the combi delivers an adequate supply of hot water, all you need is a
shower mixing valve to blend hot and cold - rather than an electric

shower.


Not sure I understand your first point, what I thought about doing would be
a "Y" shaped connection with the hot (from combi) and the mains cold coming
in at the top bits of the Y and then the shower being supplied from the the
down bit. The water should draw from both supplies?

Unfortunately the supply from the combi isnt that good, the mains cold is
only 11 litres per minute at best.

Cheers
Mike




  #6   Report Post  
Mike Hibbert
 
Posts: n/a
Default Why is this a bad idea?

"MrCheerful" wrote in message
...
Mike Hibbert wrote:
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one
else suggest it. I'm looking at shower options at the moment, and I
live in an area with fairly low water pressure. One of the easiest
options would be to have an electric shower, but I have hear that

the
water pressure would be even worse in winter as the shower would

need
to heat the water from a lover ambient temperature.

So, why not mix the water with hot water from the combi? I could

have
a feed fron the hot and cold water supply going into one pipe and
then feeding the electric shower. The water would be pre-warmed and
therefore could be made the same all year round. If the electric
shower wasn't raising the temperature too much it woudn't have such

a
problem delivering more water would it?

Like I say, this is based purely on my own "sort of" logic rather
than any fact, so shoot me down gently!

Cheers
Mike


There is no reason you couldn't feed the hot and cold into a
thermostatic mixer and then into an electric shower. I wanted some
more pressure for my shower so ran a large feed from the cold tank
(yes I know you haven't got one, but you could add one) into a pump
and then into a high power shower unit, this works fine and you can't
get scalded by someone flushing the loo.



Hi,

when you say a "high power shower unit" do you mean an electric shower? If
so, what sort of wattage is it and what sort of flow rate can you get?

cheers
mike


  #7   Report Post  
Mike Hibbert
 
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Default Why is this a bad idea?

"Andy Hall" wrote in message
...
On Wed, 27 Aug 2003 20:11:32 GMT, "Mike Hibbert"
wrote:

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be

made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than

any
fact, so shoot me down gently!

Cheers
Mike


I'm not sure that it's going to help you.

Electric showers are normally rated at up to about 10kW and the
pipework and shower head designed to give a fairly low flow rate.
This is because 10kW is a relatively small about of heat to add to
water to raise it from cold water mains temperature to the normal
working temperature of around 40 degrees.

You can actually do the sums. Let's say the water is at 10 degrees
coming in. You need to raise the temperature by 30 degrees, so using
Heat energy = mass x specific heat x temperature rise, we have

10000 = M x 4200 x 30

since the specific heat of water is 4200 Joules/kg

A litre of water weighs approx. 1kg so you can work out that this
amount of energy will be enough to heat approx. 0.08 litres per second
or about 4.75 litres/minute.

This equates to a disappointing shower.

A typical combi may have a power rating of 20-30 (possibly even as
much as 45kW), so under the same circumstances of needing to raise the
water temperature by 30 degrees will give you 2 to 4.5 times the flow
rate, which becomes a lot more sensible.

However, if the issue is that the water pressure, or more importantly
the flow rate is poor, then adding in more heating of the water is not
going to help.

If the issue were that the combi is under-rated and water supply is
adequate, then theoretically, adding in another source of heat would
be interesting. However, I am not sure that water regulations or the
manufacturers of electric showers would make this a feasible option.

With a flow rate issue because of the water supply, the options would
be to upgrade the water supply pipe from the street main (you would
have to pay for this unless the supply rate is *extremely* low, or to
have some form of cold water storage tank and a shower pump.


Thanks Andy, I have already looked at getting a cold water supply and then
pumping it into the combi, this could well be the best bet, but there are
lots of pitfalls for me with that (primaily being a total lack of plumbing
skills - but a willingness to learn!). I would still want to have mains tap
water at some of the sinks so would have concerns about the hot being under
pressure and the cold being much less (at the moment it is about 1 bar or
11 litres per min).
Your other option though sounds good, would I have to get intouch with the
water board and they would do the work? Presumably, this woudl mean I have
to go onto a water meter afterwards?

Cheers for the help

Mike


  #8   Report Post  
Roger Mills
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
"Roger Mills" wrote in message
...

I don't profess to be an expert on combis - but surely, if you connect

the
output of the combi to a cold supply at mains pressure, you won't have

any
flow through the combi - because the input and output will be at the

same
pressure.



Not sure I understand your first point, what I thought about doing would

be
a "Y" shaped connection with the hot (from combi) and the mains cold

coming
in at the top bits of the Y and then the shower being supplied from the

the
down bit. The water should draw from both supplies?


Er, no! As I understand it, the only thing that makes water flow through the
combi is the pressure difference between input and output. In other words,
the input is at mains pressure and the output is at a much lower pressure -
equal to the back pressure generated by the flow going through the pipework
and open tap(s).

However, if you connect the combi output to a source of mains pressure
through a Y-piece, you immediately raise the output to mains pressure - thus
removing the differential. Don't forget that pressure is homogeneous - and
acts equally in all directions - so there's no inherent reason why flow
can't come down one branch of the Y and go back up the other branch rather
than along the down pipe.

You might still get *some* flow through the combi, because there will be a
small amount of back pressure in the cold feed to the Y-piece, but the vast
majority of the water is going to take the line of least resistance - which
is the direct feed to the Y-piece, by-passing the combi. So you will be
little better off than if you simply took the cold mains straight to the
electric shower.

Roger


  #9   Report Post  
Andy Hall
 
Posts: n/a
Default Why is this a bad idea?

On Wed, 27 Aug 2003 20:54:08 GMT, "Mike Hibbert"
wrote:

"Andy Hall" wrote in message
.. .
On Wed, 27 Aug 2003 20:11:32 GMT, "Mike Hibbert"
wrote:

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be

made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than

any
fact, so shoot me down gently!

Cheers
Mike


I'm not sure that it's going to help you.

Electric showers are normally rated at up to about 10kW and the
pipework and shower head designed to give a fairly low flow rate.
This is because 10kW is a relatively small about of heat to add to
water to raise it from cold water mains temperature to the normal
working temperature of around 40 degrees.

You can actually do the sums. Let's say the water is at 10 degrees
coming in. You need to raise the temperature by 30 degrees, so using
Heat energy = mass x specific heat x temperature rise, we have

10000 = M x 4200 x 30

since the specific heat of water is 4200 Joules/kg

A litre of water weighs approx. 1kg so you can work out that this
amount of energy will be enough to heat approx. 0.08 litres per second
or about 4.75 litres/minute.

This equates to a disappointing shower.

A typical combi may have a power rating of 20-30 (possibly even as
much as 45kW), so under the same circumstances of needing to raise the
water temperature by 30 degrees will give you 2 to 4.5 times the flow
rate, which becomes a lot more sensible.

However, if the issue is that the water pressure, or more importantly
the flow rate is poor, then adding in more heating of the water is not
going to help.

If the issue were that the combi is under-rated and water supply is
adequate, then theoretically, adding in another source of heat would
be interesting. However, I am not sure that water regulations or the
manufacturers of electric showers would make this a feasible option.

With a flow rate issue because of the water supply, the options would
be to upgrade the water supply pipe from the street main (you would
have to pay for this unless the supply rate is *extremely* low, or to
have some form of cold water storage tank and a shower pump.


Thanks Andy, I have already looked at getting a cold water supply and then
pumping it into the combi, this could well be the best bet, but there are
lots of pitfalls for me with that (primaily being a total lack of plumbing
skills - but a willingness to learn!). I would still want to have mains tap
water at some of the sinks so would have concerns about the hot being under
pressure and the cold being much less (at the moment it is about 1 bar or
11 litres per min).
Your other option though sounds good, would I have to get intouch with the
water board and they would do the work? Presumably, this woudl mean I have
to go onto a water meter afterwards?

Cheers for the help

Mike


Another thing that you could do, if you have the space is to add in
what amounts to a conventional hot water system on a small scale.

This would consist of a roof tank for the cold water and a smallish
hot water cylinder. You would need to run the coil of the hot water
tank by connecting it across the central heating circuit and using a
motorised diverter valve. Your existing CH controller may be able
to handle the control aspect of this but otherwise a fairly
inexpensive one will do. The principle would be that the CH would
work as it does today, but that a thermostat on the cylinder which
would operate when the water needs heating, would move the motorised
valve over so that the CH water goes through the cylinder coil, and
would also fire up the boiler. In this way of working (which is
standard for non-combi systems) the boiler really doesn't know that
it's being asked to provide heat that's going to a HW cylinder rather
than the radiators.

You could use the hot water from this cylinder just to run the shower
or possibly the bath as well if you wanted. Both the hot and the
cold water for the shower would be derived from the roof tank and a
pump could be included to boost the pressure and flow at the shower -
all completely safely. The combi output could continue to feed all
the other taps that in any case don't usually need as much flow rate,
and also you would have a mains derived supply at both taps in such
cases - i.e. equal pressures. I agree with you that it doesn'[t
seem to safe an idea to have high pressure hot and low pressure cold.

The results that you could get at the shower would be limited only by
the size of tank and cylinder - so you need to think about what flow
rate you want (10 -15 litres/min is good) and how long you want the
shower to run before the cylinder ran out of hot water. Another thing
that this arrangement does is to allow you to have the hot water
stored at 60 degrees. Thus even if the boiler is a bit undersized it
doesn't really matter too much and if you mix hot water at 60 with
cold water at 10 or less, you are not limited by what the combi can do
directly.

All told in materials, not including shower and pump, this should be
under £200 - 250. A good shower pump by Stuart Turner can be had for
about £150.

In effect, this approach removes the limitations of the water supply
and of the combi, if any.

It's worth seeing whether the water supplier will do anything,
although the requirement from Ofwat is minimal on what they are
required to provide. If you want more then you would have to pay
for new pipework from the road, which depending on what's involved may
not be cheap. As you say, if they can find a way to get you on a
meter, they will.


..andy

To email, substitute .nospam with .gl
  #10   Report Post  
BigWallop
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!

Cheers
Mike



If the output from the boiler and main water supply are openly connected
together in a tee fitting, you'll also get cold water flowing back toward
any hot taps you turn on.

Can't you just install a wider diameter pipe, say 22mm, directly from the
main supply to the shower and then reduce it to 15mm as close to the shower
as possible. This should give you enough pressure to run an instant shower
from all year round.




  #11   Report Post  
IMM
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be

to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a

lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a

feed
fron the hot and cold water supply going into one pipe and then feeding

the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!


Mike,

You have the making of a good idea with some trimming. There have been some
odd suggestions from people on this thread. A combi will do the shower no
problem even in winter, as they put in a lot kWs. So first option is a
thermostatic mixer valve fed from the combi's hot supply. Also gas is 1/4
of the price of electricity.

For backup you could have between the combi's hot outlet and the taps and
shower mixer an instant in-line electric heater. These have
thermosstatically controlled water temp. When on electric this will give a
trickle of a shower, and service one tap at a time, but fine for backup.
Normally you keep this switched off and the hot water produced by the combi
will run straight through it (any water throttle on the electric heater just
keep fully open). If incoming cold mains temperature is an issue then the
electric in-line heat can be switched on to boost the combi. I doubt if this
will ever occur.

In-line electric heaters are about £80-100 from major suppliers and I
believe Screwfix now do one. They can be fitted in the loft, or under sinks,
etc. they are not that big.



---
--

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Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003


  #12   Report Post  
IMM
 
Posts: n/a
Default Why is this a bad idea?


"Christian McArdle" wrote in message
t...
Like I say, this is based purely on my own "sort of" logic rather
than any fact, so shoot me down gently!


If the problem is that the street can only supply 11 litres per minute and
you want more, then you will need a tank. No amount of piping is going to
magically double your flow rate.

If your flow rate from the mains is only 11 litres per minute, then your
supply is not suitable for a combi anyway. The installer should have

checked
this and not installed such an unsuitable system.

Options:

a) If the supply in the street is OK, you may be able to upgrade your

supply
to something decent like 25mm MDPE which will give you much better flow.

b) You can install a large tank in the loft to run a shower. You will need

a
pump to pressurise the water as it leaves the tank. This pump can also

feed
other taps (i.e. the bath) or you can use an all in one power shower which
only feeds the shower.


If you go to the bother of installing a tank in the loft, then have the pump
supply the combi. Simple. A double feed pump that will have two tappings
off the tank and one leg supplies only the combi and the other the cold
water oulets, except the cold water tap at the kitchen.



---
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Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003


  #13   Report Post  
Mike Hibbert
 
Posts: n/a
Default Why is this a bad idea?

"IMM" wrote in message
...

"Mike Hibbert" wrote in message
...
"Roger Mills" wrote in message
...

"Mike Hibbert" wrote in message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one

else
suggest it. I'm looking at shower options at the moment, and I live

in
an
area with fairly low water pressure. One of the easiest options

would
be
to
have an electric shower, but I have hear that the water pressure

would
be
even worse in winter as the shower would need to heat the water from

a
lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could

have
a
feed
fron the hot and cold water supply going into one pipe and then

feeding
the
electric shower. The water would be pre-warmed and therefore could

be
made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more

water
would it?

Like I say, this is based purely on my own "sort of" logic rather

than
any
fact, so shoot me down gently!

Cheers
Mike


I don't profess to be an expert on combis - but surely, if you connect

the
output of the combi to a cold supply at mains pressure, you won't have

any
flow through the combi - because the input and output will be at the

same
pressure.

If the combi delivers an adequate supply of hot water, all you need is

a
shower mixing valve to blend hot and cold - rather than an electric

shower.


Not sure I understand your first point, what I thought about doing would

be
a "Y" shaped connection with the hot (from combi) and the mains cold

coming
in at the top bits of the Y and then the shower being supplied from the

the
down bit. The water should draw from both supplies?

Unfortunately the supply from the combi isnt that good, the mains cold

is
only 11 litres per minute at best.


Putting in a separate electric shower will achieve nothing at all. Poor
flow and pressure will always be there with a combi or an electric shower.

Firstly, I would get the mains pipe uprated from the street stopcock.

This
is necessary, so should be done. Secondly have the supply to the combi

from
the house stop cock uprated to 22mm if the new mains does not improve
matters substantially. It is a matter of working back from the mains

supply
and seeing how matters perform, then eliminating the next obvious
bottleneck.

Even if you have a poor flow and pressure in your district, I assume this
will not last forever, so uprating the mains will pay dividends when the
district is uprated.


Yeah, this is a good point, but (and this is a big but....) we are currently
not on a meter and really dont want to be on one. We have a fairly large
pond and what with evaporation, this would be expensive to keep topped up.
If we upgraded anything, the water board would (I expect) want us to go onto
a meter.

Mike


  #14   Report Post  
Ed Sirett
 
Posts: n/a
Default Why is this a bad idea?

Mike Hibbert wrote:

Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one else
suggest it. I'm looking at shower options at the moment, and I live in an
area with fairly low water pressure. One of the easiest options would be to
have an electric shower, but I have hear that the water pressure would be
even worse in winter as the shower would need to heat the water from a lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could have a feed
fron the hot and cold water supply going into one pipe and then feeding the
electric shower. The water would be pre-warmed and therefore could be made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering more water
would it?

Like I say, this is based purely on my own "sort of" logic rather than any
fact, so shoot me down gently!


Get you combi boiler to do the work. Even a poor quality one half filled
with chalk will still out perform any domestic electric shower.

Put you money into upgrading the shower mixer to a thermostatic unit.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
  #15   Report Post  
Suz
 
Posts: n/a
Default Why is this a bad idea?

Unfortunately the supply from the combi isnt that good, the mains cold
is
only 11 litres per minute at best.


Putting in a separate electric shower will achieve nothing at all. Poor
flow and pressure will always be there with a combi or an electric shower.

Firstly, I would get the mains pipe uprated from the street stopcock.

This
is necessary, so should be done. Secondly have the supply to the combi

from
the house stop cock uprated to 22mm if the new mains does not improve
matters substantially. It is a matter of working back from the mains

supply
and seeing how matters perform, then eliminating the next obvious
bottleneck.

Even if you have a poor flow and pressure in your district, I assume this
will not last forever, so uprating the mains will pay dividends when the
district is uprated.


A further question on the same topic.
We have fantastic pressure as far as I can tell. Only the kitchen tap is
directly connected to the mains at the minute and you can turn it full on
without soaking yourself. However I have asked Waterline what the pressure
is, to check everything out for a combi, and am waiting 3 weeks later for
some-one to get back to me...
This may be a stupid question , but is it possible we would need to get our
mains supply uprated for a combi supplying 2 showers, 1 bath and all the
other usual stuff? I wonder if we have good pressure but a small pipe and
performance can't be measured by the kitchen tap. How do I check what size
ours is? Sorry I know this is really really basic for you guys, but I know
so little, and am a bit of a give-it-a-go Jane.

Ta
Suzanne




  #16   Report Post  
Andy Hall
 
Posts: n/a
Default Why is this a bad idea?

On Thu, 28 Aug 2003 19:41:49 +0100, "Suz" wrote:




A further question on the same topic.
We have fantastic pressure as far as I can tell. Only the kitchen tap is
directly connected to the mains at the minute and you can turn it full on
without soaking yourself. However I have asked Waterline what the pressure
is, to check everything out for a combi, and am waiting 3 weeks later for
some-one to get back to me...


There is an assortment of information at

http://www.ofwat.gov.uk/aptrix/ofwat.../waterpressure

The key point regarding what the water supplier has to do is

"The DG2 measure is ten metres head of pressure, at the external stop
tap, at a flow of nine litres per minute. This should be sufficient to
fill a one-gallon container in 30 seconds. This level of pressure does
not override the duty to supply water constantly at a pressure to
reach the upper floors of properties. "

The important point is to differentiate between static and dynamic
pressure and flow rate.

The static pressure at a given point is the pressure with no water
flow. If you were to connect a pressure gauge at your kitchen tap
and there is no flow into the house the (static) pressure will be the
same as at the external stop tap. If you then start drawing water
into your house, the pressure at the kitchen tap will drop, possibly
markedly. At the external stop tap and especially the water main,
it may drop a little, but if the distributionsystem is well
engineered, it should not be by very much. The longer and the
thinner the communication pipe from the water main to your kitchen
tap, the greater the pressure drop under *dynamic* conditions will be.
The greater the flow that you draw into your house, the greater the
pressure drop as well.

So this is why it can be interesting to upgrade the communication
pipe, but only if the pressure outside at the main is worthwhile.
You will notice that Ofwat only makes the water suppliers deliver 9
litres/minute at 10 metres head of pressure at the external stop cock.
This is a very poor standard indeed and is probably something that
they can easily meet. It would be just about enough to supply one
shower directly, but not brilliantly, and certainly not two.



This may be a stupid question , but is it possible we would need to get our
mains supply uprated for a combi supplying 2 showers, 1 bath and all the
other usual stuff? I wonder if we have good pressure but a small pipe and
performance can't be measured by the kitchen tap.


What rate are you getting at the kitchen tap?

It is possible that the communication pipe is small and would benefit
from being upgraded. However, this can be expensive to do since you
have to pay. You would really need to have measurements taken to be
sure, but I wouldn't commit to anything in terms of upgrades or boiler
changes until you know where you stand.

How do I check what size
ours is? Sorry I know this is really really basic for you guys, but I know
so little, and am a bit of a give-it-a-go Jane.


You can check the pipe size by using a caliper gauge to measure the
diameter directly or you can wrap a thread around the pipe and
carefully measure the length. Divide by pi (3.14) to get the
external diameter of the pipe.


Ta
Suzanne


..andy

To email, substitute .nospam with .gl
  #17   Report Post  
Suz
 
Posts: n/a
Default Why is this a bad idea?

Once again Andy, thanks a million.


  #18   Report Post  
IMM
 
Posts: n/a
Default Why is this a bad idea?


"Mike Hibbert" wrote in message
...
"IMM" wrote in message
...

"Mike Hibbert" wrote in message
...
"Roger Mills" wrote in message
...

"Mike Hibbert" wrote in

message
...
Hi all,

I'm guessing that this is a pretty daft idea as I have seen no-one

else
suggest it. I'm looking at shower options at the moment, and I

live
in
an
area with fairly low water pressure. One of the easiest options

would
be
to
have an electric shower, but I have hear that the water pressure

would
be
even worse in winter as the shower would need to heat the water

from
a
lover
ambient temperature.

So, why not mix the water with hot water from the combi? I could

have
a
feed
fron the hot and cold water supply going into one pipe and then

feeding
the
electric shower. The water would be pre-warmed and therefore could

be
made
the same all year round. If the electric shower wasn't raising the
temperature too much it woudn't have such a problem delivering

more
water
would it?

Like I say, this is based purely on my own "sort of" logic rather

than
any
fact, so shoot me down gently!

Cheers
Mike


I don't profess to be an expert on combis - but surely, if you

connect
the
output of the combi to a cold supply at mains pressure, you won't

have
any
flow through the combi - because the input and output will be at the

same
pressure.

If the combi delivers an adequate supply of hot water, all you need

is
a
shower mixing valve to blend hot and cold - rather than an electric
shower.


Not sure I understand your first point, what I thought about doing

would
be
a "Y" shaped connection with the hot (from combi) and the mains cold

coming
in at the top bits of the Y and then the shower being supplied from

the
the
down bit. The water should draw from both supplies?

Unfortunately the supply from the combi isnt that good, the mains cold

is
only 11 litres per minute at best.


Putting in a separate electric shower will achieve nothing at all. Poor
flow and pressure will always be there with a combi or an electric

shower.

Firstly, I would get the mains pipe uprated from the street stopcock.

This
is necessary, so should be done. Secondly have the supply to the combi

from
the house stop cock uprated to 22mm if the new mains does not improve
matters substantially. It is a matter of working back from the mains

supply
and seeing how matters perform, then eliminating the next obvious
bottleneck.

Even if you have a poor flow and pressure in your district, I assume

this
will not last forever, so uprating the mains will pay dividends when the
district is uprated.


Yeah, this is a good point, but (and this is a big but....) we are

currently
not on a meter and really dont want to be on one. We have a fairly large
pond and what with evaporation, this would be expensive to keep topped up.
If we upgraded anything, the water board would (I expect) want us to go

onto
a meter.


Do some water consumption calculations. Most people are pleasantly
surprised at how cheap being on a meter can be. Inquire, you may not be
forced onto a meter.


---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003


  #19   Report Post  
IMM
 
Posts: n/a
Default Why is this a bad idea?


"Suz" wrote in message
...
Unfortunately the supply from the combi isnt that good, the mains cold

is
only 11 litres per minute at best.


Putting in a separate electric shower will achieve nothing at all. Poor
flow and pressure will always be there with a combi or an electric

shower.

Firstly, I would get the mains pipe uprated from the street stopcock.

This
is necessary, so should be done. Secondly have the supply to the combi

from
the house stop cock uprated to 22mm if the new mains does not improve
matters substantially. It is a matter of working back from the mains

supply
and seeing how matters perform, then eliminating the next obvious
bottleneck.

Even if you have a poor flow and pressure in your district, I assume

this
will not last forever, so uprating the mains will pay dividends when the
district is uprated.


A further question on the same topic.
We have fantastic pressure as far as I can tell. Only the kitchen tap is
directly connected to the mains at the minute and you can turn it full on
without soaking yourself. However I have asked Waterline what the

pressure
is, to check everything out for a combi, and am waiting 3 weeks later for
some-one to get back to me...
This may be a stupid question , but is it possible we would need to get

our
mains supply uprated for a combi supplying 2 showers, 1 bath and all the
other usual stuff? I wonder if we have good pressure but a small pipe and
performance can't be measured by the kitchen tap. How do I check what

size
ours is? Sorry I know this is really really basic for you guys, but I

know
so little, and am a bit of a give-it-a-go Jane.


Check the flow rate by using a bucket. How many litres per minute?
Pressure in some combi's is not a major issue as they can operate on very
low pressure. As long as the flow rate is there they will operate very well.


---
--

Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003


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