i was at my mates and he lives in a social housing block,anyways he'd just had his gas fire done (dfe),cp 12. and he got a copy and i had a look,the engineer had put n.c.s. regarding terminal/chimney stack, to me it was a normal stack with an aliminum ?terminal,the kind you can join to a liner,does any body no why this would be n.c.s.