Kitchen ventilation

I Am just starting to refit our kitchen, there is a 9"x9" hole in the wall (ducted straight to outside) where the previous owners removed the bricks and didn't bother to put on a grill on the inside. As the first part of the refit the old boiler has been ripped out, this had a conventional flue which went straight up the chimney, the new boiler will be room sealed. I would like to block up the hole in the wall as the wind howls through this and keeps the kitchen cold (there is no rad), 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? 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?

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.

Cheers

Martin

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

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'

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However I am aware that there are some

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.

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.