I'd appreciate some Corgi insight please. I have a gas cooker in a kitchen within a house so it does not have an opening window or door to the outside. I do have a 6 to 8 inch diameter bore through the cavity wall from the kitchen to the outside world - it runs diagonally to make it passed the extension that was added to the house. This held a fan until I was recently told that there was inadequate ventilation. There is no air brick so what diameter of hole is required to comply with the ventilation regs. At the moment the kitchen is cold and drafty as there is a seemingly great big ventilation shaft. What diameter of vent is required and must the shaft be lined? I hope someone good folks can assist me.

