Vent sizes for gas boiler in cupboard

chocolatepennyfarthing

Hi, does anyone know the amount and sizes of the vent/airways that should be on door to a cupboard in which a gas boiler is fitted.
Its a large brick built cupboard so vents need to go in door. (warm air heating system).

st999

My warm air heating unit is in a cupboard in the kitchen and I had the choice of getting a vent knocked out of an outside wall at a BG cost of £200 or removing the cupboard door.

I removed the cupboard door.

Before anyone starts I know I could get it done cheaper elsewhere, In fact I could have done it myself for free. Removing the cupboard door was the most MSE way.