In article ,
Ian Stirling writes:

I'm fairly sure it's fine. It'd be a couple of meters higher than the
existing one, which is not over a path, or anywhere close to a boundary,
and further from windows/openings than existing ones.
I was more wondering about routing the condensate.

Sounds OK to me. IIRC, mine required 21mm (overflow pipe) indoors,
and 32mm minimum outdoors where it might be subject to freezing.
I guess the loft might get cold even when boiler is on, so you
might want to take precautions. You could probably put 22mm pipe
insulation over the 21mm overflow pipe in the loft. Might want to
keep the length of run to the 110mm soil stack as short as possible,
particulary the outdoor part of it. Condensate is still slightly
warm on mine when it runs into the pipe, so it would probably be
quite difficult to get it to freeze inside the loft area.

--
Andrew Gabriel