How to Install a Furnace Flue Pipe

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Things You'll Need

  • Single-wall galvanized pipe

  • Single-wall galvanized elbows

  • Sheet metal screws

  • Cordless drill

  • Aviation snips

  • Pipe crimper

  • 1-inch galvanized hanger strap

  • Work gloves

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Natural gas furnaces are efficient appliances and widely used to heat homes. When burning a fuel for combustion, that combustion gas must be carried outside. Furnace flue pipes exhaust these toxic combustion gases out of the building. Without exhausting these gases outside, they will build up in the home and harm the occupants. When you install a furnace flue pipe, you are ensuring the comfort and safety of the occupants.

Step 1

Measure the distance from the furnace to the chimney. You should already have a connection on the chimney where the old flue pipe attached to the previous furnace.

Step 2

Purchase single-wall galvanized pipe and elbows from your local home improvement store. These must match the size of your furnace's flue pipe outlet.

Step 3

Install the flue pipe to the chimney connection, starting at the furnace. The flue pipe is connected together by inserting the "crimped end" of each pipe into the "non-crimped end" of each pipe. Each joint is screwed together with at least four sheet metal screws. Cut the galvanized pipe as necessary with your aviation snips if you need a length shorter than the standard lengths. Crimp one end of the cut piece with your pipe crimper.

Step 4

Hang your flue pipe from the ceiling joists using 1-inch galvanized hanger strap. Screw one end up the hanger strap to the ceiling joist and then loop it around the flue pipe. Take the other end of the strap up to the ceiling joist to the location you want to fasten it and cut the excess strap off. Screw that end to the ceiling joist. The hanger should look like the letter U and the flue pipe should sit in the middle of the U.


If your chimney doesn't have a location for the flue pipe, you may need to core a hole with a concrete coring machine into the chimney. The size would depend on your furnace's flue pipe connection. You would core a hole 1/4 to 1/2 inch bigger than the outer diameter of the pipe. The pipe then slips into the hole and is sealed with a high-temperature silicone caulk.

Pitch the flue pipe up toward the chimney. This allows the hot combustion gases to to move into the chimney easier. Hot air will want to rise, so that is the reasoning for pitching the flue pipe upward.


Furnace flue pipe is extremely sharp. It can cause severe cuts and injury if handled improperly. Wear work gloves when handling flue pipe.


Elizabeth Knoll

Elizabeth Knoll has been writing full-time since 2008. She has a deep love for gardening and has spent a vast amount of time researching that subject. Her work appears on various websites. Knoll received a certificate in Early Childhood Education from Moraine Park Technical College.