Hi folks,

need your advice on pipe size - what would you recommend (15mm or
22mm) as a supply (cold) to and flow (hot) from combi boiler to taps?
Boiler can produce 14 ltrs/min so one would think that 15mm pipe is
enough. However there are opinions that 22mm is preferred because
boiler will get priority in getting cold water.

thanks for any info,

"olo" wrote in message
oups.com...
Hi folks,

need your advice on pipe size - what would you recommend (15mm or
22mm) as a supply (cold) to and flow (hot) from combi boiler to taps?
Boiler can produce 14 ltrs/min so one would think that 15mm pipe is
enough. However there are opinions that 22mm is preferred because
boiler will get priority in getting cold water.

Have a dedicated pipe from the stoptap to the combi with nothing teed off
except the cold to the showers just before the combi. Also have the shower
hot direct from the combi, and again a dedicated supply. 22mm would be
better for the reasons you stated, however 15mm should be fine if a
dedicated cold feed.

On 13 Jul, 13:24, olo wrote:
Hi folks,

need your advice on pipe size - what would you recommend (15mm or
22mm) as a supply (cold) to and flow (hot) from combi boiler to taps?
Boiler can produce 14 ltrs/min so one would think that 15mm pipe is
enough. However there are opinions that 22mm is preferred because
boiler will get priority in getting cold water.

thanks for any info,

On my combi the tail at the bottom of the boiler for taking cold water
is 15mm, and so I guess is the pipework within the boiler. In this
case I can't see any benefit it having 22mm pipe from the main, or am
I missing something?

Anita Palley wrote:
On 13 Jul, 13:24, olo wrote:
Hi folks,

need your advice on pipe size - what would you recommend (15mm or
22mm) as a supply (cold) to and flow (hot) from combi boiler to taps?
Boiler can produce 14 ltrs/min so one would think that 15mm pipe is
enough. However there are opinions that 22mm is preferred because
boiler will get priority in getting cold water.

thanks for any info,

On my combi the tail at the bottom of the boiler for taking cold water
is 15mm, and so I guess is the pipework within the boiler. In this
case I can't see any benefit it having 22mm pipe from the main, or am
I missing something?


flow rate is not limited exactly by pipe bore alone, its a function of
pressure, length and bore.

So if you want flow rates to be high, use large bore wherever you can.

The downside is the space it tales up, the heat that may be locked
inside it and lost, and the cost.

I tend to think in terms of 22mm almost everywhere, these days.

"Anita Palley" wrote


On my combi the tail at the bottom of the boiler for taking cold water
is 15mm, and so I guess is the pipework within the boiler. In this
case I can't see any benefit it having 22mm pipe from the main, or am
I missing something?

Yes

15mm pipe from the stoptap to the boiler with associated elbows etc creates
a pressur drop.
Using 22mm right up to the 15mm boiler connection guarantees minimal losses
before the boiler.

Phil

"TheScullster" wrote in message
...

"Anita Palley" wrote


On my combi the tail at the bottom of the boiler for taking cold water
is 15mm, and so I guess is the pipework within the boiler. In this
case I can't see any benefit it having 22mm pipe from the main, or am
I missing something?

Yes

15mm pipe from the stoptap to the boiler with associated elbows etc
creates a pressur drop.
Using 22mm right up to the 15mm boiler connection guarantees minimal
losses before the boiler.

Yep! You could have 25 litres/min and 3.5 bar at the stoptap and with
lengthy 15mm pipe with elbows have 20 litres/min at the end and much reduced
pressure at the end of the pipe.

"The Natural Philosopher" wrote in message
...
Anita Palley wrote:
On 13 Jul, 13:24, olo wrote:
Hi folks,

need your advice on pipe size - what would you recommend (15mm or
22mm) as a supply (cold) to and flow (hot) from combi boiler to taps?
Boiler can produce 14 ltrs/min so one would think that 15mm pipe is
enough. However there are opinions that 22mm is preferred because
boiler will get priority in getting cold water.

thanks for any info,

On my combi the tail at the bottom of the boiler for taking cold water
is 15mm, and so I guess is the pipework within the boiler. In this
case I can't see any benefit it having 22mm pipe from the main, or am
I missing something?


flow rate is not limited exactly by pipe bore alone, its a function of
pressure, length and bore.

So if you want flow rates to be high, use large bore wherever you can.

The downside is the space it tales up, the heat that may be locked inside
it and lost, and the cost.

I tend to think in terms of 22mm almost everywhere, these days.


Also hot water takes longer to come through a 22mm pipe - the volume of the
pipe is proportional to the square of the radius (or diameter), the flow
rate to some lesser power. This means it's brill once the hot water has
arrived, as the flow is larger, but there's a longer period flushing out the
cold.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Also hot water takes longer to come through a 22mm pipe - the volume of the
pipe is proportional to the square of the radius (or diameter), the flow
rate to some lesser power. This means it's brill once the hot water has
arrived, as the flow is larger, but there's a longer period flushing out the
cold.

Fair point.

Considering all opinions so far - how about 22mm dedicated cold supply
from stopcock to boiler and then 15mm from boiler to shower/taps. This
will minimise pressure drop on the cold side and give shortest waiting
time for the hot water.

Also hot water takes longer to come through a 22mm pipe - the volume of the
pipe is proportional to the square of the radius (or diameter), the flow
rate to some lesser power. This means it's brill once the hot water has
arrived, as the flow is larger, but there's a longer period flushing out the
cold.

Fair point.

Considering all opinions so far - how about 22mm dedicated cold supply
from stopcock to boiler and then 15mm from boiler to shower/taps. This
will minimise pressure drop on the cold side and give shortest waiting
time for the hot water

"olo" wrote in message
oups.com...
Also hot water takes longer to come through a 22mm pipe - the volume of
the
pipe is proportional to the square of the radius (or diameter), the flow
rate to some lesser power. This means it's brill once the hot water has
arrived, as the flow is larger, but there's a longer period flushing out
the
cold.

Fair point.

Considering all opinions so far - how about 22mm dedicated cold supply
from stopcock to boiler and then 15mm from boiler to shower/taps. This
will minimise pressure drop on the cold side and give shortest waiting
time for the hot water.

Sounds good. Have the shower hot back to the combi and cold top the shower
taken off the combi just before the cold inlet. Have a shower mixer with
pressure equalisation valve inside. Or fit one at the combi on the two
shower lines.

In article ews.net,
"Doctor Drivel" writes:
Sounds good. Have the shower hot back to the combi and cold top the shower
taken off the combi just before the cold inlet. Have a shower mixer with
pressure equalisation valve inside. Or fit one at the combi on the two
shower lines.

Use a thermostatic shower designed for combi and multipoints,
i.e. high pressure cold and widely varying pressure hot and
very fast reaction to temp changes. They work extremely well.

Pressure equalisation valves on a combi where the hot water
pressure changes significantly as the load changes don't work
at all well with a shower (unless perhaps you are the only
person in the house). You need a fast acting thermostatic
valve anyway, so just get the right type in the first place.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Fri, 13 Jul 2007 16:00:13 +0000, olo wrote:

Also hot water takes longer to come through a 22mm pipe - the volume of the
pipe is proportional to the square of the radius (or diameter), the flow
rate to some lesser power. This means it's brill once the hot water has
arrived, as the flow is larger, but there's a longer period flushing out the
cold.

Fair point.

Considering all opinions so far - how about 22mm dedicated cold supply
from stopcock to boiler and then 15mm from boiler to shower/taps. This
will minimise pressure drop on the cold side and give shortest waiting
time for the hot water

That would be my choice if starting from scratch, except that I would not
bother with a 'dedicated' supply if doing it in 22mm. I would try to make
sure the boiler's cold supply is upstream of most/all other usage points.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs he http://www.makewrite.demon.co.uk/GasFittingStandards

"Andrew Gabriel" wrote in message
...
In article ews.net,
"Doctor Drivel" writes:
Sounds good. Have the shower hot back to the combi and cold top the
shower
taken off the combi just before the cold inlet. Have a shower mixer with
pressure equalisation valve inside. Or fit one at the combi on the two
shower lines.

Use a thermostatic shower designed for combi and multipoints,
i.e. high pressure cold and widely varying pressure hot and
very fast reaction to temp changes. They work extremely well.

You will find these integrated equalisation valves.

Pressure equalisation valves on a combi where the hot water
pressure changes significantly as the load changes don't work
at all well with a shower (unless perhaps you are the only
person in the house). You need a fast acting thermostatic
valve anyway, so just get the right type in the first place.

You need primarily a valve with a pressure equalisation valve inside. The
thermostatic part is very secondary.

"Ed Sirett" wrote in message
...
On Fri, 13 Jul 2007 16:00:13 +0000, olo wrote:

Also hot water takes longer to come through a 22mm pipe - the volume of
the
pipe is proportional to the square of the radius (or diameter), the flow
rate to some lesser power. This means it's brill once the hot water has
arrived, as the flow is larger, but there's a longer period flushing out
the
cold.

Fair point.

Considering all opinions so far - how about 22mm dedicated cold supply
from stopcock to boiler and then 15mm from boiler to shower/taps. This
will minimise pressure drop on the cold side and give shortest waiting
time for the hot water

That would be my choice if starting from scratch, except that I would not
bother with a 'dedicated' supply if doing it in 22mm. I would try to make
sure the boiler's cold supply is upstream of most/all other usage points.

Which is near impossible in most cases.

I would try to make sure the boiler's cold supply is upstream of most/all other
usage points.

Which is near impossible in most cases.

=)

well it is impossible in my case, but I know what's important now,
thanks for all your help, much appreciated

In article ews.net,
Doctor Drivel wrote:
Yep! You could have 25 litres/min and 3.5 bar at the stoptap and with
lengthy 15mm pipe with elbows have 20 litres/min at the end and much
reduced pressure at the end of the pipe.

And this comes from a self styled expert? The pressure stays the same,
prat. The flow rate alters.

--
*And don't start a sentence with a conjunction *

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message
...
In article ews.net,
Doctor Drivel wrote:
Yep! You could have 25 litres/min and 3.5 bar at the stoptap and with
lengthy 15mm pipe with elbows have 20 litres/min at the end and much
reduced pressure at the end of the pipe.

And
Pleese eff off as you a total and utter idiot.

The Natural Philosopher wrote:

So if you want flow rates to be high, use large bore wherever you can.

Not much point if the combi can only heat it at 14 l/min. Draw water
faster and it will just be cooler.


--
Cheers,

John.

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