On Fri, 10 Oct 2003 12:51:04 +0100, a particular chimpanzee named
"Martin Crook" randomly hit the
keyboard and produced:

...the new boiler will be room sealed... and it is probably too close to
where the new flue will have to exit the wall - could anyone clarify the
minimum distance for me?

A boiler flue should be at least 300mm between an opening for a
fanned-flue, or between 300mm-600mm to the side or above an opening
for a natural draught flue depending on the output (see diagram 3.4 of
AD 'J' [http://tinyurl.com/qjn7])

However I am aware that there are some
ventilation requirements for kitchens, so do I have to make another vent
somewhere else (presumably cavity sealed, ie ducted to outside) if I block
it and what size does it have to be? In addition there is no cooker
extractor at present, do I have to put one in or can I leave it without - as
it is now?

The ventilation opening would have been sized for the boiler rather
than for background ventilation, so it would be acceptable to reduce
the size of the vent opening to 4000mm² (IIRC, a 225mm x 75mm air
brick with a closeable grille, or trickle vents in a window)

You're not required to provide an extract fan if there isn't one
already, but as one who's lived in houses with and without them, I
would recommend that you do. The existing open-flued boiler acted as
an extract fan, and you may find that the condensation level will rise
once it's removed.

As an aside, what should I do about blocking the disused chimney, I would
rather seal this up, as I don't want a gaping hole above the new boiler, I
was just going to plasterboard across the entrance and make it part of the
existing alcove ceiling that the boiler sits in. If I do this do I need a
vent into the chimney stack to keep it dry, there is an existing hatch on
the outside, which I presume was for sweeping, I could easily put a grill on
this.

You definitely need to ventilate the chimney (usually by a small
grille internally); not sure if that should be by a grille in the
outside. I would have thought that might lead to problems by
introducing cold air into the flue causing (rather than removing)
condensation, and negating any stack effect.
--
Hugo Nebula
"You know, I'd rather see this on TV,
Tones it down" - Laurie Anderson