"Rod" wrote in message
...
We currently have an older gas boiler which is open-flue. It is in a
cupboard (all right, a compartment) which has a door.

We wish to replace this door (because it is tatty). But we need to fit
ventilation grilles. I *know* I found calculations for the requirements
somewhere when last I looked. Now I can't. (I just find references to
sites which have the information for a fee such as BSI.)

The boiler is something like 12 to 15 KW. We need to provide air inflow
for combustion plus air in/out for moderating the temperature in the
cupboard. (I *know* we should get a condensing boiler... :-) )

What effective area ventilation grilles are required? Or where can I
find the calaculations?

--
Rod

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A compartment ventilated to a room or internal space requires 10 cm2 per
kilowatt (net) of the boiler maximum rated input at high level. Low level
requires 20 cm2 per kilowatt (net)
You should find the rating information on the plate fixed to the boiler.
Grills should be non closable and not covered in any mesh/flyscreen etc.