how to install a chimney liner for a gas furnace

Installing a chimney liner for a gas furnace is an important step to ensure safe venting of combustion gases from the furnace to the outside. It is crucial to follow safety guidelines and local building codes when doing this installation. Here’s a general guide on how to install a chimney liner for a gas furnace:

Materials You’ll Need:

  • Chimney liner kit suitable for gas furnaces (flexible or rigid)
  • Chimney liner adapter and cap
  • Gas-rated sealant
  • Aluminum foil tape
  • Wire brush or chimney cleaning tools
  • Vent pipe (if needed)
  • Measuring tape
  • Screwdriver and screws
  • Utility knife
  • Work gloves
  • Safety glasses
  • Ladder or scaffolding


  1. Safety Precautions:
    • Before you start, turn off the gas supply to the furnace and make sure it’s cool. Also, ensure that the chimney is clean and free of obstructions.
  2. Choose the Right Liner:
    • Select a chimney liner kit that is appropriate for your gas furnace and complies with local building codes. The liner can be either flexible or rigid, depending on your chimney’s configuration.
  3. Measure the Chimney:
    • Measure the length and diameter of the chimney to determine the appropriate liner size. The liner should fit snugly inside the chimney.
  4. Prepare the Liner:
    • If you’re using a flexible liner, unroll it and straighten it out as much as possible. If you’re using a rigid liner, ensure it is cut to the correct length.
  5. Install the Adapter:
    • Attach the chimney liner adapter to the top of the furnace’s flue collar. Secure it using screws and ensure it is airtight. Apply gas-rated sealant around the connection for added security.
  6. Insert the Liner:
    • Carefully insert the chimney liner into the chimney from the top, with the adapter end leading. Have someone assist you from below to guide the liner down the chimney.
  7. Secure the Liner:
    • At the top of the chimney, secure the chimney liner to the chimney crown using appropriate clamps or hardware provided in the kit. Make sure the liner is centered and well-supported.
  8. Seal the Joints:
    • Seal the joints between sections of flexible liner using aluminum foil tape or approved chimney liner sealant. Ensure there are no gaps or leaks.
  9. Install the Cap:
    • Attach the chimney liner cap to the top of the liner to prevent rain, debris, and animals from entering the chimney. Secure it in place as per the manufacturer’s instructions.
  10. Connect to the Furnace:
    • Connect the other end of the chimney liner to the adapter on the furnace’s flue collar. Ensure a tight fit, use approved sealant, and secure it with screws if necessary.
  11. Inspect and Clean:
    • Visually inspect the entire installation to ensure all connections are secure, and there are no gaps or loose parts. Clean up any debris or excess sealant.
  12. Reconnect Gas Supply:
    • Turn the gas supply back on and check for any gas leaks around the furnace connections. Use a gas leak detection solution to verify there are no leaks.
  13. Test the Furnace:
    • Turn on the gas furnace and observe its operation. Ensure that the flue gases are properly venting through the chimney liner.
  14. Comply with Codes and Regulations:
    • Ensure that your installation meets local building codes and regulations, and if required, have it inspected by the relevant authorities.

Chimney liner installation for a gas furnace should be done carefully and in compliance with safety guidelines and local codes. If you’re not experienced with this type of installation or if you have any doubts, it’s advisable to seek the assistance of a licensed HVAC professional or chimney specialist to ensure a safe and proper installation.

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