Hi I have just installed a spinflo gas cooker with two rings and a grill I was going to put a couple of mushroom type roof vents above cooker but when I was in caravan shop asking for advice there was a chap in shop from Scottish caravan services who told me I had to calculate area of van against btus or bthus (I think it was something like that) for carbon monoxide can anybody give me some guidance please. I obviously want to do the right thing to complete my conversion........Bruce