As per header...............

The new combi condensing boiler has a 10 litre pressure vessel but does
not say what the maximum system volume is before you need to add an
additional expansion vessel.....

Also although I know the number of metres of 22mm and 15mm pipe I have
used (and hence can calculate the volume), how can I do this for the 14
Rads when the brochure does not state their internal liquid volume?

My pipe volume is 50% higher as I have two heating zones, upstairs and
downstairs so am using more 22mm tube than usual.

I have a tactic for measuring the system volume when I finally fill the
system... read the water meter before and after, and subtract... :-)

Regards,

Stephen.

On 17/01/2012 21:59, Stephen H wrote:

The new combi condensing boiler has a 10 litre pressure vessel but does
not say what the maximum system volume is before you need to add an
additional expansion vessel.....

Also although I know the number of metres of 22mm and 15mm pipe I have
used (and hence can calculate the volume), how can I do this for the 14
Rads when the brochure does not state their internal liquid volume?

My pipe volume is 50% higher as I have two heating zones, upstairs and
downstairs so am using more 22mm tube than usual.

I have a tactic for measuring the system volume when I finally fill the
system... read the water meter before and after, and subtract... :-)

There is a formula you can use...

If V is the expansion volume in litres, p1 is the absolute starting
pressure, p2 the maximum pressure, and e is an expansion factor based on
maximum system temperature, you get:

Total system volume = V x ( 1-(p1/p2) ) / e

For a system max temperature of 85 deg C, e is 0.0324

If you fill your system to 1 bar that gives you an absolute pressure of
2 bar (i.e. add 1 bar atmospheric to it)

If you decide the maximum pressure you want to run at is 2.75 bar, then
that's an absolute pressure of 3.75.

So your 10 litre expansion vessel allows:

10 x ( 1-(2/3.75) ) / 0.0324 = 144 litres



--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
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On Tue, 17 Jan 2012 21:59:30 +0000, Stephen H wrote:

As per header...............

The new combi condensing boiler has a 10 litre pressure vessel but does
not say what the maximum system volume is before you need to add an
additional expansion vessel.....

Also although I know the number of metres of 22mm and 15mm pipe I have
used (and hence can calculate the volume), how can I do this for the 14
Rads when the brochure does not state their internal liquid volume?

My pipe volume is 50% higher as I have two heating zones, upstairs and
downstairs so am using more 22mm tube than usual.

I have a tactic for measuring the system volume when I finally fill the
system... read the water meter before and after, and subtract... :-)

Regards,

Stephen.

The PDFs on
http://www.stelrad.com/uk/downloads.php
give the volumes for Stelrad radiators.
Assuming that yours are similar, the figures should be near enough.
--
Peter.
The gods will stay away
whilst religions hold sway

On Jan 17, 9:59*pm, Stephen H wrote:
As per header...............

The new combi condensing boiler has a 10 litre pressure vessel but does
not say what the maximum system volume is before you need to add an
additional expansion vessel.....

Also although I know the number of metres of 22mm and 15mm pipe I have
used (and hence can calculate the volume), how can I do this for the 14
Rads when the brochure does not state their internal liquid volume?

My pipe volume is 50% higher as I have two heating zones, upstairs and
downstairs so am using more 22mm tube than usual.

I have a tactic for measuring the system volume when I finally fill the
system... read the water meter before and after, and subtract... * * :-)

Regards,

Stephen.

IIRC it is usually somewhere between 2% and 5% (but I honestly have
only little idea on this and would recommend you find an official
source). It really depends on what is the maximum circulation
temperature your system has been designed for. Although it might be a
reasonable idea to fit a bigger expansion vessel to cope with a one-
off burn-up of 90 deg C, in practical terms, you should not ever
require an average system temp over 70degC and it would be fair to
assume that this, 90degC, would be a rare requirement, the current
expansion vessel will either cope with it or you will lose some
heating water through the pressure relief valve. If you ever require
these high temperatures and you suspect there has been a water loss
(due to a high pressure indication), then it would be a good idea to
leave the heating on constant at a reduced burner setting to reduce
the contraction of the water, during the exceptional cold spell. This
would mean if a top-up is required because a top radiator did not
heat, it would only be the once when the weather was warmer.