When is an exhaust thimble required?

Ventilated thimbles are mandated by NFPA-37 where exhaust piping penetrates through combustible walls or combustible roofs. Even in seemingly “non-combustible” walls/roofs, it may be a good idea to provide an insulated thimble to protect against burning of roof sealers, coatings, stucco, etc. Wall and roof thimbles are available in carbon steel or stainless steel. You may request a proposal for a wall or roof thimble here.