§ 27-894 Thimbles.
AC § 27-894
(a)When passing through combustible constructions, bent connectors constructed of type B gas vent material shall be installed so that the clearances required by the standard are maintained.
(b)Vent connections made of single-wall metal pipe shall not pass through any combustible walls or partitions unless they are guarded at the point of passage by ventilated metal thimbles not smaller than the following: (1) For equipment conforming to standards – four inches larger in diameter than the vent connector.
(2)For equipment having draft hoods – six inches larger in diameter than the vent connector.
(3)For equipment without draft hoods – twelve inches larger in diameter than the vent connector.
