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    DuraFlex Chimney Liner Installation Guide

    DuraFlex by Simpson Duravent is a flexible relining system for masonry chimneys. DuraFlex SS (Stainless Steel) is for use with gas, wood pellet, oil, or wood appliances, including: fireplace inserts, furnaces, boilers, and water heaters. DuraFelex AL (Aluminum) is for use with natural gas or liquid propane category I, draft hood equipped appliances, and appliances tested and listed to use Type B Gas Vent for a wide range of applications, including: natural gas fireplaces, gas-fired furnaces, boilers, water heaters, and wall or space heating applications.

    DuraFlex SS systems are OMNI Listed to UL 1777 and ULC S635 (43-P-02-2). DuraFlex AL systems are UL Listed to UL 1777 (MH14420).


    • The inner pipe diameter should match the outlet size of the appliance.
    • Check the appliance manufacturer's installation instructions to confirm which types of vent configurations are permitted (i.e. horizontal, vertical, chimney reline, etc.). Also, check for any venting restrictions such as maximum horizontal run, minimum and maximum vertical rise, maximum offset, etc.
    • Be fire safe! Use proper support and bracing. Follow local building codes and have your venting system inspected.



    Planning Your Installation

    1. Verify the venting requirements of the appliance used. Choose the liner system appropriate for the appliance and installation.

    2. Refer to the Typical Installations for the type of liner installation similar to your situation. Identify the needed parts for installation.

    3. The size of the liner should match the outlet size on the appliance or the size of the vent/manifold that penetrates into the masonry chimney.

    4. Determine the length of liner needed.

    5. Make sure of a proper fit for the Top Plate of the reliner to provide a secure, leak-proof installation.

    6. If a free-standing appliance is used, select the vent or stovepipe pieces to connect from the appliance to the liner (refer to the appropriate item page for manual).

    7. Important! Check to be sure the installation complies with all local and national code requirements, including clearance to combustibles. Contact the local building inspector for permit requirements.

    Design Recommendations

    The following design recommendations are intended only as a general guideline to assist in the design and selection of liner components for your installation. Always read and follow Simpson Dura-Vent Installation instructions (enclosed with the cap or support box) before installing DuraFlex. Installation instructions can be viewed online by downloading the manual on the items page.

    Before relining a chimney, it should be cleaned and inspected to verify the integrity of the mortar and masonry. In addition, have a certified chimney professional determine if the masonry was constructed with 0" or 1" clearance to the surrounding combustibles. This is an important fire safety issue that may have an influence on how the liner is installed.

    Be sure to select the proper liner for the application.

    • DuraFlex SS is used for appliances that use oil, wood, or wood-pellets for fuel.
    • DuraFlex AL is for a non-condensing gas appliance.

    Refer to the appliance manufacturer for installation requirements affecting venting. Keep the vent path as straight as possible for best performance.

    About the Author

    Collin Champagne

    Approaching his 10-year work anniversary, Collin is one of our National Fireplace Institute (NFI) certified technicians and content manager for the eFireplacestore, eCanopy, and EliteDeals brands. He is a Master Hearth Professional, which means he is certified in all three hearth appliance fields—wood, gas and pellet.

    When not at work, he spends time with his wife, Lindsey, and his sons, Samuel and Eli, on their ranch enjoying their many animals. Completing projects around the ranch and spending quality time with his family are among his greatest joys. 

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