On Sat, 12 Aug 2006 16:43:53 +0100, Doctor Drivel wrote:

The primary does not have to be vented at all. The cylinder can be
heated via a coil and the primaries a part of a sealed unvented system.
The only time they require venting, is if the cylinder is being heated
directly.

The primary _does_ have to be vented if you are using an ordinary
direct cylinder which is what we were talking about. Or actually what
_you_ were talking about and what I followed up on.

I know, you know, you know that I know and I know that you know that
thermal stores can be heated indirectly, but this is not what we were
talking about.