The 28 HE cannot use
plastic drain piping for the flue.

Very interesting but not relevant as original poster hasn't got a 28HE

At the risk of supporting IMM on this one,

That must kill you; an amateur supporting a pro.

No, obviously sometimes you say something sensible. You can't always be
wrong. Indeed, I quite like the way that there is often a kernel of an idea
in much of what you say, but it is often not thought through and you always
back yourself into a corner by not admitting which parts are sensible and
which are not, possibly not even to yourself.

Also, the tendency to believe anything said by a man in a white coat, with
no recourse to scientific evidence, is quite endearing.

Christian.