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.
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.
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.
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.
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.