Abstract: A chimney having concentric tubular walls defining an annular pressurized space includes a sealing arrangement having a flexible boot with one edge connected to one of the walls. The top hood or cover supported on the inner wall of the chimney includes a lower annular surface which extends over the outer wall. Spring biased support members supported on the outer walls are connected to an annular seal ring to which a second flexible edge of the boot is connected and supports the same in sealing relation against the lower annular surface of the hood to seal the annular space and accomodate relative movement of the walls resulting from natural elements.