DuraVent 30deg Elbow Kit Use for offsets around obstructions such as rafters, ridgepoles, or joists. Offsets greater than 30 Degree are not permitted in accordance to the UL 103 standards. Elbow swivels at 360 Degree at base (angles are not adjustable). A pair of elbows is required to return an offset chimney back to vertical. Manufacturer's Limited Lifetime Warranty.