Hi,

I am having my house replumbed with a new CH/HW system. I was
expecting that the plumber would use 22mm pipe for the hot water to
the combi boiler. However he has used 15mm pipe, and most of it
plastic.

Can anyone point me to some information so I can calculate the
pressure losses. The 15mm pipe may be OK. I've no idea about plastic
pipe. Unfortunately I have to be at work while the plumber is here so
I cannot speak to him in person. If there is a real problem I need to
know so that I can take a week off work to sort it out.

The house concerned is 4 bed, 2 bath with a 20ltr/min combi boiler.
The boiler is in a attached garage.

Thanks for reading this post.

Yours Faithfully,
John.

John wrote:
Hi,

I am having my house replumbed with a new CH/HW system. I was
expecting that the plumber would use 22mm pipe for the hot water to
the combi boiler. However he has used 15mm pipe, and most of it
plastic.

That's normal: you'll find the connections to the boiler are 15mm for
mains cold water in and DHW out, and 22mm for CH flow and return.
(Anomalously the gas inlet is often 1/2" BSP although most of the gas
pipework has to be in 22mm.)


Can anyone point me to some information so I can calculate the
pressure losses. The 15mm pipe may be OK. I've no idea about plastic
pipe.

Plastic pipe is fine (except that the connections to most boilers are
still specified to be in copper for the first metre or so). What plastic
loses on the slightly smaller internal diameter it probably makes up for
by making smooth bends.


The house concerned is 4 bed, 2 bath with a 20ltr/min combi boiler.

Even at that relatively (for a combi) high flow rate the boiler itself
is likely to be the limiting factor to the flow and delivery pressure
achievable.

If you were having an unvented cylinder or heat store fitted, and
especially if your incoming mains pressure were on the low side or your
pipe runs had to be _very_ long, then 22mm pipework would be indicated.

On Fri, 07 Jan 2005 23:05:38 +0000, John Stumbles
wrote:

Thanks very much for taking the time to reply to my post.

John wrote:
Hi,

I am having my house replumbed with a new CH/HW system. I was
expecting that the plumber would use 22mm pipe for the hot water to
the combi boiler. However he has used 15mm pipe, and most of it
plastic.

That's normal: you'll find the connections to the boiler are 15mm for
mains cold water in and DHW out, and 22mm for CH flow and return.
(Anomalously the gas inlet is often 1/2" BSP although most of the gas
pipework has to be in 22mm.)

The connections to the boiler are 15mm but the installation
instructions states that "A 22mm hot water distribution pipe to the
first branch is recommended ...".

Can anyone point me to some information so I can calculate the
pressure losses. The 15mm pipe may be OK. I've no idea about plastic
pipe.

Plastic pipe is fine (except that the connections to most boilers are
still specified to be in copper for the first metre or so). What plastic
loses on the slightly smaller internal diameter it probably makes up for
by making smooth bends.


The house concerned is 4 bed, 2 bath with a 20ltr/min combi boiler.

Even at that relatively (for a combi) high flow rate the boiler itself
is likely to be the limiting factor to the flow and delivery pressure
achievable.

If you were having an unvented cylinder or heat store fitted, and
especially if your incoming mains pressure were on the low side or your
pipe runs had to be _very_ long, then 22mm pipework would be indicated.

The boiler is quite a long way from the rising main. I estimate there
will be nearly 20m with 2 right angle joints and 2 tees.

Why I am concerned is that, when I moved in, the mains flow rate was
quite poor (about 16 litres/min). When we removed some kitchen
cabinets we discovered that somebody had cut the 22mm supply pipe just
after the stop cock and routed a 15mm pipe under the sink, put another
stop tap in on the 15mm pipe, and then rejoined to the 22mm pipe
further up. Thereby introducing about 2m of 15mm pipe.

When the 22mm pipe was reinstated with a reducing tee to the sink the
mains cold flow doubled. Therefore I am now quite skeptical that 15mm
pipe is adequate. I have tried to get the mains pressure tested, but
all I got from the experts was "It's fine".

Thanks and Regards,
John

"John Stumbles" wrote in message
...


Anomalously the gas inlet is often 1/2" BSP although most of the gas
pipework has to be in 22mm.)

And sometime in 28mm. I believe the calulation of the pipe size is down to
the number of bends and length of the gas pipe along with the power rating
of the gas appliance.

Adam

There is a flow restrictor in the combi which reduces flow far more than any length of 15mm pipe.

I find it quite surprising that you noticed a difference in cold water flow by removal of a short length of 15mm pipe.

If you have problems then maybe your local water mains pressure is down. All that the water bord have to do is supply water to your tap, there is no requirement for you to get a good shower.

The solution for poor water pressure is to store sufficient water inside your house and pump it with a 3 bar heavy duty pump either to your combi or to an unvented cylinder or through a thermal store.

On Sat, 8 Jan 2005 19:14:24 +0000, Paul Barker
wrote:

Thanks for the reply.

There is a flow restrictor in the combi which reduces flow far more
than any length of 15mm pipe.

I know there is a restriction in the boiler but I thought that the
losses in the pipework is cumulative.

I find it quite surprising that you noticed a difference in cold water
flow by removal of a short length of 15mm pipe.

It made a huge difference, but the stop-cock was replaced at the same
time so maybe that was the problem.

If you have problems then maybe your local water mains pressure is
down. All that the water bord have to do is supply water to your tap,
there is no requirement for you to get a good shower.

The solution for poor water pressure is to store sufficient water
inside your house and pump it with a 3 bar heavy duty pump either to
your combi or to an unvented cylinder or through a thermal store.

I've measured the static water pressure near the main and it's just
over 3 bar. It doesn't drop much when the kitchen tap is switched on.

Regards,
John

"John" wrote in message
...
Hi,

I am having my house replumbed with a new CH/HW system. I was
expecting that the plumber would use 22mm pipe for the hot water to
the combi boiler. However he has used 15mm pipe, and most of it
plastic.

Can anyone point me to some information so I can calculate the
pressure losses. The 15mm pipe may be OK. I've no idea about plastic
pipe. Unfortunately I have to be at work while the plumber is here so
I cannot speak to him in person. If there is a real problem I need to
know so that I can take a week off work to sort it out.

The house concerned is 4 bed, 2 bath with a 20ltr/min combi boiler.
The boiler is in a attached garage.

Thanks for reading this post.

John,

The problem with mains pressure systems: combi, unvented cylinder, thermal
store, is that one appliance may rob another of pressure. The most critical
is the shower. You don't want fluctuations on this for scalding and
discomfort reasons. Companies like Gledhill recommend a dedicated supply
from the stop cock to the appliance (combi) only. Also from the mains stop
cock they recommended a dedicated cold supply to the shower.

A 15mm pipe may be adequate, but it is the balancing of the mains water that
is important.

I would recommend:

1. A full bore stop cock.
2.. A dedicated 22mm supply to the combi from the stop cock.
3. Tee off at the stoop cock and run all cold outlets from this, except the
shower (s).
4. Take the cold for the shower off the combi cold feed just before the
combi. Any pressure fluctuations on this line with be pretty equal on cold
and hot.
5. Insert in-line restrictors on some appliances like the dishwasher,
w/machine etc. They don't require full flow to operate. Also on basin
taps, etc. In short ensure the hot for the combi takes all the supply and
the shower is least effected.
6. If necessary a pressure erqualising valve to the shower or one built-in
to the mixer. (about £20 in B&Q)

Having one pipe from the stop cock snaking around the house supplying all
appliances and the combi merely being one of them is foolish, unless you
have 10 bar pressure and 1" supply, or the likes of.

Plastic pipe restricts flow and pressure. The inserts reduce a 15mm pipe
bore to 12mm.

John wrote:

On Fri, 07 Jan 2005 23:05:38 +0000, John Stumbles
wrote:

Thanks very much for taking the time to reply to my post.


John wrote:

Hi,

I am having my house replumbed with a new CH/HW system. I was
expecting that the plumber would use 22mm pipe for the hot water to
the combi boiler. However he has used 15mm pipe, and most of it
plastic.

That's normal: you'll find the connections to the boiler are 15mm for
mains cold water in and DHW out, and 22mm for CH flow and return.
(Anomalously the gas inlet is often 1/2" BSP although most of the gas
pipework has to be in 22mm.)


The connections to the boiler are 15mm but the installation
instructions states that "A 22mm hot water distribution pipe to the
first branch is recommended ...".


Can anyone point me to some information so I can calculate the
pressure losses. The 15mm pipe may be OK. I've no idea about plastic
pipe.

Plastic pipe is fine (except that the connections to most boilers are
still specified to be in copper for the first metre or so). What plastic
loses on the slightly smaller internal diameter it probably makes up for
by making smooth bends.



The house concerned is 4 bed, 2 bath with a 20ltr/min combi boiler.

Even at that relatively (for a combi) high flow rate the boiler itself
is likely to be the limiting factor to the flow and delivery pressure
achievable.

If you were having an unvented cylinder or heat store fitted, and
especially if your incoming mains pressure were on the low side or your
pipe runs had to be _very_ long, then 22mm pipework would be indicated.


The boiler is quite a long way from the rising main. I estimate there
will be nearly 20m with 2 right angle joints and 2 tees.

Why I am concerned is that, when I moved in, the mains flow rate was
quite poor (about 16 litres/min). When we removed some kitchen
cabinets we discovered that somebody had cut the 22mm supply pipe just
after the stop cock and routed a 15mm pipe under the sink, put another
stop tap in on the 15mm pipe, and then rejoined to the 22mm pipe
further up. Thereby introducing about 2m of 15mm pipe.

When the 22mm pipe was reinstated with a reducing tee to the sink the
mains cold flow doubled. Therefore I am now quite skeptical that 15mm
pipe is adequate. I have tried to get the mains pressure tested, but
all I got from the experts was "It's fine".


I would say that really to get best flow you should use the largest bore
pipe almst everywhere, just taking it down to small bore for the actual
taps and room work itself.

Especially long runs.

Size does matter, and bigger is better, and the only downside is expense
and the actual physcal fitment.

Thanks and Regards,
John

I would say that really to get best flow you should use the largest bore
pipe almst everywhere, just taking it down to small bore for the actual
taps and room work itself.

Especially long runs.

Size does matter, and bigger is better, and the only downside is expense
and the actual physcal fitment.

Thanks and Regards,
John


and the other downsides are ....
a) there is a LOT of cold water in the hot tap supply pipe (about double ?)
that has to be discarded before hot water reaches the tap - time delay - I
replaced our 22mm pipe
from the hot tank to the kitchen / utility room sinks (approx 15 metres length)
with 15 mm and the time
delay was about halved (Gravity) flow rate is just fine...

b) ....and the heat wasted (small but nevertheless present) in the non-heating
months.

"nick smith" wrote in message
...
I would say that really to get best flow you should use the largest bore
pipe almst everywhere, just taking it down to small bore for the actual
taps and room work itself.

Especially long runs.

Size does matter, and bigger is better, and the only downside is expense
and the actual physcal fitment.

Thanks and Regards,
John


and the other downsides are ....
a) there is a LOT of cold water in the hot tap supply pipe (about double
?)
that has to be discarded before hot water reaches the tap - time delay - I
replaced our 22mm pipe
from the hot tank to the kitchen / utility room sinks (approx 15 metres
length)
with 15 mm and the time
delay was about halved (Gravity) flow rate is just fine...

b) ....and the heat wasted (small but nevertheless present) in the
non-heating
months.

You can put a secondary circulation pump on eliminating draw-off dead-leg
time lag.

As IMM is demonstrating the cure for, the fact you measure 3bar static presssure is meaningless, you need to know the capacity of the supply. You would measure 3 bar through a pinhole.

I also agree with the last guy. I would maximise pipe size to the heat source/cylinder, and then use just sufficient to obtain the flow you require so that you are not waiting too long for hot water and wasting heat and water.

On Sun, 09 Jan 2005 14:51:39 GMT, "nick smith"
wrote:

I would say that really to get best flow you should use the largest bore
pipe almst everywhere, just taking it down to small bore for the actual
taps and room work itself.

Especially long runs.

Size does matter, and bigger is better, and the only downside is expense
and the actual physcal fitment.

Thanks and Regards,
John


and the other downsides are ....
a) there is a LOT of cold water in the hot tap supply pipe (about double ?)
that has to be discarded before hot water reaches the tap - time delay - I
replaced our 22mm pipe
from the hot tank to the kitchen / utility room sinks (approx 15 metres length)
with 15 mm and the time
delay was about halved (Gravity) flow rate is just fine...

Yes, but a lot of the pipework only carries cold water, so I don't
care about any heat losses there :-) Also for a sink getting the hot
water quickly is more important than the flow rate. For a bath the
opposite applies.

b) ....and the heat wasted (small but nevertheless present) in the non-heating
months.

Regards,
John

On Sun, 09 Jan 2005 12:27:16 +0000, John wrote:

On Sat, 8 Jan 2005 19:14:24 +0000, Paul Barker
wrote:

Thanks for the reply.


It made a huge difference, but the stop-cock was replaced at the same
time so maybe that was the problem.

Based on my experience and what you have said I would say "very likely".

Go with the 15mm DHW pipework.

The 22 to the first branch is probably the manufacturers covering their
corporate behinds. It will eliminate slightly the effect of two draw off
points being used together (but in fact the boiler is the limiting factor
- overwhelmingly).

--
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

"John" wrote in message
...

Yes, but a lot of the pipework only carries cold water, so I don't
care about any heat losses there :-) Also for a sink getting the hot
water quickly is more important than the flow rate. For a bath the
opposite applies.

The cost of water in modern well insulated homes with condensing boilers is
now more than space heating. Wasting a little energy in a secondary
circulation loop to give:

1. No waiting for hot water at the taps
2. saving 3 litres of water each time you wash your hands.

May be financial beneficial.

All of a secondary circulation draw-off loop has to be lagged.

nick smith wrote:

I would say that really to get best flow you should use the largest bore
pipe almst everywhere, just taking it down to small bore for the actual
taps and room work itself.

Especially long runs.

Size does matter, and bigger is better, and the only downside is expense
and the actual physcal fitment.


Thanks and Regards,
John



and the other downsides are ....
a) there is a LOT of cold water in the hot tap supply pipe (about double ?)
that has to be discarded before hot water reaches the tap - time delay - I
replaced our 22mm pipe
from the hot tank to the kitchen / utility room sinks (approx 15 metres length)
with 15 mm and the time
delay was about halved (Gravity) flow rate is just fine...

b) ....and the heat wasted (small but nevertheless present) in the non-heating
months.



Yup. I fogot those - valid points.

IMM wrote:

"nick smith" wrote in message
...

I would say that really to get best flow you should use the largest bore
pipe almst everywhere, just taking it down to small bore for the actual
taps and room work itself.

Especially long runs.

Size does matter, and bigger is better, and the only downside is expense
and the actual physcal fitment.


Thanks and Regards,
John


and the other downsides are ....
a) there is a LOT of cold water in the hot tap supply pipe (about double

?)

that has to be discarded before hot water reaches the tap - time delay - I
replaced our 22mm pipe
from the hot tank to the kitchen / utility room sinks (approx 15 metres

length)

with 15 mm and the time
delay was about halved (Gravity) flow rate is just fine...

b) ....and the heat wasted (small but nevertheless present) in the

non-heating

months.


You can put a secondary circulation pump on eliminating draw-off dead-leg
time lag.



...and waste even more heat as you essentially have a small radiator there.

"The Natural Philosopher" wrote in message
...
IMM wrote:

"nick smith" wrote in message
...

I would say that really to get best flow you should use the largest
bore
pipe almst everywhere, just taking it down to small bore for the actual
taps and room work itself.

Especially long runs.

Size does matter, and bigger is better, and the only downside is
expense
and the actual physcal fitment.


Thanks and Regards,
John


and the other downsides are ....
a) there is a LOT of cold water in the hot tap supply pipe (about double

?)

that has to be discarded before hot water reaches the tap - time delay -
I
replaced our 22mm pipe
from the hot tank to the kitchen / utility room sinks (approx 15 metres

length)

with 15 mm and the time
delay was about halved (Gravity) flow rate is just fine...

b) ....and the heat wasted (small but nevertheless present) in the

non-heating

months.


You can put a secondary circulation pump on eliminating draw-off
dead-leg
time lag.



..and waste even more heat as you essentially have a small radiator there.

See my post about water costs.

On Mon, 10 Jan 2005 00:10:10 +0000, Ed Sirett
wrote:

On Sun, 09 Jan 2005 12:27:16 +0000, John wrote:

On Sat, 8 Jan 2005 19:14:24 +0000, Paul Barker
wrote:

Thanks for the reply.


It made a huge difference, but the stop-cock was replaced at the same
time so maybe that was the problem.

Based on my experience and what you have said I would say "very likely".

Go with the 15mm DHW pipework.

The 22 to the first branch is probably the manufacturers covering their
corporate behinds. It will eliminate slightly the effect of two draw off
points being used together (but in fact the boiler is the limiting factor
- overwhelmingly).

What about the cold supply to the boiler? Should that be 15mm or
22mm, given that its about 16m from the rising main.

Regards,
John

The message
from "IMM" contains these words:

The cost of water in modern well insulated homes with condensing boilers is
now more than space heating.

A perfect illustration of dIMMs lack of joined up thinking. For years he
has been claiming that the payback time for replacing any old boiler
with an expensive condensing boiler is only a few years (without any
qualification by type of house or, indeed type of old boiler). But if
his statement above is true then there is no way any saving in running
costs of said expensive new boiler would do as much as cover the
interest lost on the capital used to fund the new installation.

--
Roger

"John" wrote in message
...
On Mon, 10 Jan 2005 00:10:10 +0000, Ed Sirett
wrote:

On Sun, 09 Jan 2005 12:27:16 +0000, John wrote:

On Sat, 8 Jan 2005 19:14:24 +0000, Paul Barker
wrote:

Thanks for the reply.


It made a huge difference, but the stop-cock was replaced at the same
time so maybe that was the problem.

Based on my experience and what you have said I would say "very likely".

Go with the 15mm DHW pipework.

The 22 to the first branch is probably the manufacturers covering their
corporate behinds. It will eliminate slightly the effect of two draw off
points being used together (but in fact the boiler is the limiting factor
- overwhelmingly).

What about the cold supply to the boiler? Should that be 15mm or
22mm, given that its about 16m from the rising main.

At that length make it 22mm most of not all of the way. Larger reduces
pressure and flow losses and the likelihood of one outlet affecting another.

"Roger" wrote in message
k...
The message
from "IMM" contains these words:

The cost of water in modern well insulated homes with condensing boilers
is
now more than space heating.

A perfect illustration

snip drivel

I blame Tony Blair for allowing people like this at keyboards.

The message
from "IMM" contains these words:


The cost of water in modern well insulated homes with condensing boilers
is now more than space heating.

A perfect illustration

snip drivel

'Drivil' reinstated

A perfect illustration of dIMMs lack of joined up thinking. For years he
has been claiming that the payback time for replacing any old boiler
with an expensive condensing boiler is only a few years (without any
qualification by type of house or, indeed type of old boiler). But if
his statement above is true then there is no way any saving in running
costs of said expensive new boiler would do as much as cover the
interest lost on the capital used to fund the new installation.


dIMM, if that really was drivel you would have waded in with both feet
citing reams of compelling figures but it isn't and you can't. I don't
think you have ever come up with any rational figures that weren't the
product of someone elses effort. So come on dIMM, now is your chance to
shine - so put up or shut up.

I blame Tony Blair for allowing people like this at keyboards.

In your perfect socialist state only you and Tony Blair would be free to
do what they want and I can't see even Bliar lasting very long.

--
Roger

"Roger" wrote in message
k...
The message
from "IMM" contains these words:


The cost of water in modern well insulated homes with condensing
boilers
is now more than space heating.

A perfect illustration


snip drivel

I blame Tony Blair for allowing people like this at keyboards.