On Sun, 9 May 2004 20:45:09 +0100, "Vortex"
wrote:

Hi,

Shortly I want to upgrade my gas central heating from "vented" to "sealed"
(primary reason to eliminate the loft tank to make way for a future loft
conversion.....secondary benefit is that I'll be able to put a rad up
there.)

Both good reasons, and there are several more if you look in Ed
Sirett's FAQ on it.



On investigating the "tide marks" in my header tank I calculate system
expansion to be about 3 litres in normal use. This is consistent with a
system volume of about 100 litres...which seems plausible to me (4 bed
house).

Good old bes.ltd.uk sell expansion vessels in 8, 12, 18, 24 litre (and
larger) sizes.

Is there a rule of thumb for specifying the correct expansion vessel? At
first glance an 8 litre one would seem adequate...but the price difference
is so minimal I'm inclined towards an 18 litre one (there's plenty of
space). Is there any penalty in using a vessel that's too large?

You can certainly go larger, and there is no reason not to do so. I
have a boiler with a 10 litre vessel built in, but on calculating the
size, it might have been marginal, so I added another one also of 10
litres.



While I'm at it I want to put in "bleed valve" on a spur off the main boiler
flow (actually this is where the fill and vent pipes will be removed) for
easy introduction of Fernox. Is this normal practice? Seems to make a lot
of sense to me.

Yes you can do that, although you may prefer to put it at a higher
point. If you are adding a normal system dose of MB-1 it's 4 litres
and depending on layout and drain arrangements, you might not have
enough capacity below this point.

You will also need vents at high points anyway to let air out. These
can be manual or automatic.




David



..andy

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