I am making some changes to my kitchen and adjoining dining room (no door
between them), and as my CH boiler is situated in the kitchen thought I
would just check the ventilation requirements. I have the installation
instructions for the boiler (Potterton Kingfisher, CFL70 - conventional
flue) and this states that the free area should be 84 cm sq.

Now when I did math at school, 84 cm sq meant a square measuring 84cm x
84cm, whereas 84 sq cm is only a little over 9cm x 9cm, a big difference. I
hope that the instructions actually mean the latter? If not I might just as
well take the back door off its hinges and freeze in the winter!

Just as an aside, the boiler is currently ventilated via openings at the
back to the underfloor space (between 5ft and 2ft all over the house) and
from there via 7 air bricks around the walls. This would be well in excess
of the 84 sq cm, but is there anything in the regs that disallow this?
BGas/Transco have a couple of times shut the boiler off cos they didn't
realise where the ventilation came from, and I wasn't home when they visited
to explain things.
David.