Pipe sizes for CH feed & expansion

GerardF

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Dec 4, 2001, 6:44:46 AM12/4/01

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From all you knowledgeable people out there, can anyone advise me what size
the feed and expansion pipes should be for my central heating system. I
assume that they should be the same size. The flow from the boiler is 28mm.

All the rads are in now - I'm just doing the hard bit....

cheers,

gerard

Grunff

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Dec 4, 2001, 2:20:09 PM12/4/01

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"GerardF" <nospamger...@hotmail.com> wrote in message
news:9uicvr$ei3$1...@thorium.cix.co.uk...

> From all you knowledgeable people out there, can anyone advise me what
size
> the feed and expansion pipes should be for my central heating system. I
> assume that they should be the same size. The flow from the boiler is
28mm.

I've just installed a full system in our new house, and I used 15mm plastic
for both the feed from the header tank and the expansion pipe to the header
tank (for the CH). I used 22mm for the feed from the main water header tank.

Grunff

Jim Easterbrook

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Dec 4, 2001, 3:15:09 PM12/4/01

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Grunff <ru...@yahoo.co.uk> wrote:

> "GerardF" <nospamger...@hotmail.com> wrote in message
> news:9uicvr$ei3$1...@thorium.cix.co.uk...
> > From all you knowledgeable people out there, can anyone advise me what
> size
> > the feed and expansion pipes should be for my central heating system. I
> > assume that they should be the same size. The flow from the boiler is
> 28mm.
>
>
> I've just installed a full system in our new house, and I used 15mm plastic
> for both the feed from the header tank and the expansion pipe to the header
> tank (for the CH).

I thought the rules forbid plastic for the vent pipe (expansion flows
back up the feed pipe). If your boiler goes horribly wrong the vent pipe
needs to carry all the steam it can produce, and plastic is not rated
for this.
--
Jim Easterbrook <http://www.easter.mersinet.co.uk/>

Grunff

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Dec 4, 2001, 3:52:57 PM12/4/01

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"Jim Easterbrook" <j...@easter.mersinet.co.uk> wrote in message
news:1f3wqp8.7qwjli1hxb4hsN%j...@easter.mersinet.co.uk...

I was unaware of that...

I don't think I'll replace it just yet, may be an interesting experiment ;o)

Grunff

Gerard Fradley

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Dec 4, 2001, 6:52:47 PM12/4/01

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"Jim Easterbrook" <j...@easter.mersinet.co.uk> wrote in message
news:1f3wqp8.7qwjli1hxb4hsN%j...@easter.mersinet.co.uk...

So 22mm should be fine for both then?

gerard

Dave Hannigan

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Dec 5, 2001, 3:15:07 AM12/5/01

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GerardF wrote:

Feed 15mm, Expansion 22mm and must rise continuosly until the open end is
taken back to the tank

ntl user

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Dec 5, 2001, 2:08:52 PM12/5/01

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"Dave Hannigan" <da...@dhannigangas.co.uk> wrote in message news:1007536072.20308.1@eurus...

> GerardF wrote:
>
> > From all you knowledgeable people out there, can anyone advise me what
> > size the feed and expansion pipes should be for my central heating system.

<..>

> Feed 15mm, Expansion 22mm and must rise continuosly until the open end is
> taken back to the tank

In my current house the feed is 22mm and it feeds into the high point of the 28mm gravity hot water circuit. The feed pipe itself
is vented locally to the header tank downstream of an isolation valve.

It seems to work - I wonder if it is worth changing?

I'd have expected the 15mm feed to go into the return 28mm gravity hot water circuit (downstream of zone valve) - can't see the
point of taking the cold feed all the way down to the boiler!

M

ntl user

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Dec 9, 2001, 5:28:05 PM12/9/01

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"ntl user" <ntl....@ntlworld.invalid> wrote in message news:dhuP7.3742$Fq6.4...@news11-gui.server.ntli.net...

Further investigation inspired by this thread reveals that the gravity hot water circuit is actually connected up the wrong way
round, the hot feed goes into the bottom of the tank. The boiler has been changed in the last year (previous owners) and it seems
that the connections have been switched here - there is what looks to be a relied valve on the 28mm HW return (which should be
feed!). Another job for next summer!

Dave Liquorice

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Dec 10, 2001, 4:22:05 AM12/10/01

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On Wed, 5 Dec 2001 19:08:52 -0000, ntl user wrote:

> I'd have expected the 15mm feed to go into the return 28mm gravity
> hot water circuit (downstream of zone valve) - can't see the point
> of taking the cold feed all the way down to the boiler!

Provided that both feed and expansion are always and at all times
irrespective of the state of any valves (manual or motorised) still
connected to the relevant sides of the boiler I guess it doesn't
matter. But:

1) An expansion connected as near as possible to the top of the boiler
will vent any gases (steam and/or Hydrogen and/or released air after
filling) formed in the boiler before they get into the circulating
part of the system. The feed/vent where connected to the HW cylinder
here and the nearest rads required frequent bleeding. Moved feed/vent
to the boiler no more bleeding rads...

2) The further the boiler has to push steam/boiling water along a
complicated pipe run to vent the higher the pressure in the boiler.
Non-combi domestic boilers are not pressure devices and normally not
rated much above 1 Bar or about 30' of water. Header tank in loft,
boiler on ground floor and you have not far short of 1 Bar before it
starts to get boil...

--
Cheers new...@howhill.com
Dave. Remove "spam" for valid email.