Duravent Stove Pipe DuraBlack Increaser, 6"-7"

A stovepipe increaser is a fitting that transitions from a smaller diameter stovepipe to a larger diameter chimney or stovepipe. The 6DBK-X7 is needed specifically when a wood stove or solid-fuel appliance has a 6-inch flue collar outlet but the Class A chimney system or ceiling support box it must connect to is 7-inch diameter. This size mismatch occurs when an appliance with a 6-inch outlet is installed beneath a 7-inch Class A chimney — either because the chimney was originally installed for a larger appliance, or because the chimney size required by the installation configuration is larger than the appliance outlet. The increaser resolves the mismatch by accepting the 6-inch DuraBlack stovepipe from the appliance on the small end and providing the 7-inch connection to the chimney or fitting on the large end.

DuraBlack is a single-wall stovepipe — it has only one layer of metal between the hot flue gases inside and the combustibles outside. The outer surface of DuraBlack pipe reaches very high temperatures during operation, approaching the temperature of the flue gases inside, which is why a large 18-inch clearance to combustibles is required to prevent ignition of nearby wood framing, walls, and other combustible materials. DuraTech Class A chimney pipe by contrast is a double-wall system with Thermal Tech ceramic refractory blanket insulation between the walls — this insulation keeps the outer wall surface cool even when the flue gases inside are at full operating temperature, which is why only 2 inches of clearance is required. This fundamental difference in wall construction is why DuraBlack is restricted to the short interior connector run from the appliance to the chimney, while DuraTech handles all sections that pass through building structures.

No. DuraBlack single-wall stovepipe is approved only for interior connector use — the short run of stovepipe that connects the appliance flue outlet to the base of the Class A chimney system at the ceiling support box or wall thimble. DuraBlack must not be used in any section of the vent run that passes through a ceiling framing assembly, floor assembly, attic space, wall cavity, or any exterior location. These sections require DuraTech Class A chimney pipe, which is listed for use in these locations by UL 103 HT and has the double-wall insulated construction needed to maintain safe clearances in proximity to building framing. Using DuraBlack stovepipe in place of Class A chimney through these sections is a serious fire hazard and a code violation.

DuraVent's installation guidelines and general building codes recommend keeping the single-wall connector stovepipe run — the DuraBlack section from the appliance to the Class A chimney — as short as practical. A shorter connector stovepipe run minimizes the amount of exposed hot single-wall pipe within the living space, reduces the clearance envelope required, and improves draft performance by getting the flue gases into the insulated Class A chimney as quickly as possible. The appliance manufacturer's installation instructions will specify the maximum permitted connector pipe length for the specific appliance — this varies by appliance and jurisdiction. The connector stovepipe including the 6DBK-X7 increaser must remain within the approved connector length specified for the appliance and comply with all applicable clearances to combustibles throughout the run.

A DuraBlack connector stovepipe run using the 6DBK-X7 typically includes 6-inch DuraBlack straight pipe sections from the appliance flue outlet up to the increaser, and potentially 6-inch DuraBlack elbow sections if the run must change direction between the appliance outlet and the chimney connection. The 6DBK-X7 increaser then transitions the 6-inch run to 7-inch diameter at the connection to the 7-inch Class A chimney ceiling support box or wall thimble. A separate chimney adapter may additionally be required at the ceiling support box to mechanically fasten the DuraBlack stovepipe into the support box's connection interface — the DuraTech ceiling support box requires a specific DVL/DuraBlack chimney adapter at its bottom to accept the single-wall stovepipe. The entire connector run must maintain 18 inches of clearance to all combustible surfaces throughout its length.

Yes. DuraVent offers DuraBlack increaser fittings in multiple size combinations to address the various diameter mismatches that can occur between appliance flue outlets and chimney diameters. The 6DBK-X7 transitions from 6 inches to 7 inches. The 6DBK-XS8 transitions from 6 inches to 8 inches for appliances with 6-inch outlets connecting to 8-inch Class A chimneys. Other increaser combinations are available across the DuraBlack and DVL stovepipe lines to cover different small-to-large diameter transitions. The correct increaser must be selected to match the specific diameter of the appliance's flue collar on the small end and the specific diameter of the Class A chimney or support box on the large end — both dimensions must be confirmed from the appliance's documentation and the installed or planned chimney before ordering.