How to Bring a Furnace Flue Up to Code

Roof

• 1

  Measure the height of your chimney flue to ensure that the top of the chimney is at least 3 feet above the roof. The chimney flue must also be 2 feet above anything else located within a 10-foot horizontal radius in order to avoid roof fires caused by sparks. This includes other parts of your roof, or nearby buildings.

• 2

  Install a cap or roof assembly on Type B gas vents according to manufacturer’s instructions.

• 3

  Use tables found in the National Fuel Gas Code manual to determine how far Type B gas vents with a cap 12 inches or smaller should extend above the surface of the roof. These heights vary by several feet depending on the pitch of the roof. Vents with caps larger than 12 inches must be at least 2 feet above the highest point on the roof.

• 4

  Inspect the chimney for rusted metal or damaged masonry, depending on the type of flue you have. Check for missing or damaged caps or missing or damaged top seals or crowns on top of a masonry chimney.

• 5

  Inspect flashing for signs of damage and repair or replace, if necessary. Install flashing around prefabricated chimneys that don’t already have it in order to keep rainwater out and prevent moisture damage.

Liners

• 6

  Hire a chimney sweep or other professional to inspect the chimney liner for signs of softening, cracking or other damage. Repair or replace, depending on the type of flue the furnace connects to.

• 7

  Ensure that the chimney liner is the correct size for the furnace. A certified chimney sweep can help you determine the best liner for your system. Liners that aren’t sized correctly lead to a buildup of creosote and carbon monoxide.

• 8

  Hire a certified chimney sweep to install a liner on chimneys that lack them. Gases produced by burning fuels are acidic and eat away at chimney walls. Chimneys without liners are at higher risk for fires and may also allow poisonous gases like carbon monoxide to leak into the house.

Other

• 9

  Inspect any part of the flue that’s located outside a building wall to ensure that there’s at least one-inch clearance between metal flues and combustible materials and two-inch clearance between masonry chimneys and combustible materials. This includes insulation.

• 10

  Seal any gaps you find with lightweight aluminum flashing and heat-resistant caulk. Build a metal dam between insulation and nearby chimney pipes or masonry chimneys.

• 11

  Hire a certified chimney sweep to inspect your chimney, chimney connectors and cleanouts at least once a year. Clean and repair as necessary.