How to Replace a Gas Furnace Vent Pipe

gas furnace
  • 5-10 hours
  • Advanced
  • 200-400
What You'll Need
4-inch galvanized metal duct as per requirement
Pipe crimping device
Elbow joints
Silicone caulk gun
Galvanized metal strap
A pair of thick rubber gloves
A stable ladder

Gas furnaces produce harmful gaseous products during combustion. One of these harmful agents is carbon monoxide, which in high concentration can cause death. Furnaces have vent pipes to avoid the building up of these gases in its operating area. As old vent pipes develop leaks that can culminate into a health hazard, it is highly recommended that you replace them. Follow the steps below to properly replace your gas furnace vent.

Step 1 - Take Appropriate Precautions

Turn off your furnace before doing any form of work. This will ensure that it doesn’t produce toxic gasses when you remove the vent pipe. To avoid injuring your hands when handling the sharp metal duct, wear your rubber gloves at all times. In case you need a ladder to reach up to the duct, deploy it carefully on an even surface so that it doesn’t topple over during work.

Step 2 - Remove the Old Vent Pipe

furnace vent pipe

Use a ladder to reach up to the pipes and remove it one piece after the other for convenience. The vent is composed of many pieces of metal ducting joined together by silicone caulk and screws. In any case, use the appropriate method to pry the pipes apart; a screwdriver is to be used to remove the screws and a knife to break the silicone caulk binding. Detach the metal hangers that support the piping from the ceiling and remove the pipe. Ask someone to help you, as the pipe can be long and too much work for one person to handle. Pull the pipe out of the outlet socket in the wall and inlet socket on top of the furnace.

Step 3 - Take a Few Measurements

Measure the required diameter and length of the metal ducting before purchasing it. Make sure that you use an accurate scale to make these measurements. Make a rough sketch to estimate the number of elbow joints needed to guide the pipe to the outlet. Only after noting and double-checking your measurements should you purchase the material for the new duct.

Step 4 - Install the Metal Duct

installing metal ductwork

Use the pipe crimper to attach one end of the metal duct to the exhaust outlet of the furnace. Guide it along the ceiling using metal straps that are attached to the ceiling via nails. Use elbow joints to help you guide the duct towards the wall outlet. To avoid leaks, use screws and silicone caulk to effectively connect the metal duct pieces together. Make sure that the piping doesn’t sag between metal hangers and that the pipe does not sag at the furnace exhaust outlet. This is done to ensure that the pipe leads the toxic gases up and out of the room.

Step 5 - Finish Up What We Started

It is advised that you call in a professional to inspect and approve your work. This is mandatory by law in some places and ensures that there are no leaks in the ducting.