I've just built a stud wall covering a 22mm gas pipe running up behind it, creating a box section measuring 2.4m x 80cm x 15 cm. The pipe comes in at the bottom through an external wall via sleeving and exits the top through a hole big enough to put my hand through in the ceiling, into the floor upstairs. I believe this stud wall will need to be ventilated?? Can anyone advise on vent sizes please?