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.)
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?
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.
David