3 Opener Width

What is the width of the existing opener in your room?

this helps us determine the size vent needed and quantity in each room

Because the regulations only stipulate a certain amount (5000EA) of ventilation is needed per habitable room you will only need vents in two of the openers if the openers are less than 700mm wide. 

If any of your openers are larger than 700mm you can just fit 1 vent and this will suffice