The 4" Wall Thimble is for use with 4" venting, through-the-wall installations. It provides a non-combustible clearance for vents when installing in combustible locations. It is adjustable from 3 1/2" to 6" to accommodate different wall thicknesses. The interior dimension is 4 3/4", while the outer dimension is 8 1/2". As with all of our B Vent components, it can be used with natural gas or liquid propane, Category 1 appliances.
A 1" clearance to combustible materials must be maintained.