How to Vent a Gas Furnace

man repairing a furnace
  • 4 hours
  • Intermediate
  • 50-150
What You'll Need
Gas furnace ventilation pipe
Tape measure
Elbow joints
Screwdriver
Silicone caulk

The vent pipe of your gas furnace plays an important role by carrying all toxic gases created during the combustion within the furnace out of the building. You should know how to vent a gas furnace and get rid of the harmful gases, for the health and safety of anyone living in your building.

By preventing these gases from contacting other combustible items, your vent will also prevent other possible fires.

Identify Your Vent

When venting your gas furnace, you need to know the different kinds of vents that can be installed. A direct vent will directly throw all the air into the atmosphere. Most old gas furnaces use such a mechanism, while modern furnaces use the B-pipes. These pipes are not only environmentally friendly for residential use, but also authorized for use by regulatory bodies and insurance companies.

Take Proper Measurements

Measure the distance from the furnace vent to the chimney. Purchase the correct size metal vent pipe from a home improvement store and make sure you get enough elbow joints to give the vent's path the necessary twists and turns. Use your measurements and plan the path out ahead of time so that you will know exactly how much material you will need.

The diameter of the vent pipe should always be larger than that of the gas furnace flue, ensuring that no gas escapes from the pipe. The vent pipe must overlap at each joint to prevent gas from leaking. Gas furnaces usually come with their own specifications. Adhere to them even if you are building the vent on your own.

Make the Attachments

Starting at the furnace, connect the various pipes by using the elbow joints, working your way towards the chimney. Be sure that each end of the pipe that is crimped faces the chimney. Crimping allows one pipe to connect to the next more easily.

Secure the Vent in Place

Using at least four sheet metal screws, connect the pipes together and screw tightly. If the length of the pipe is more than five feet, support the weight of the pipe with galvanized hanger straps. Simply screw in the ceiling joist and attach the galvanized hangar strap onto it using a screw before looping it under the pipe. Then, take it back again to the ceiling joist where you can screw it in.

Seal the Joints

It is extremely important to ensure there is complete air-tightness at all the joints and sections. Use silicone caulk to seal all joints and seams on the metal pipe, as well as on the gas furnace and chimney.

DISCLAIMER:

If any gaps remain and the vent isn't airtight, the toxic gases will leak back into your home. This undermines the entire purpose of venting the furnace in the first place.

Taking care of the vent on your gas furnace is extremely important, but working improperly and damaging your vent can have catastrophic results. If you're not sure you have the necessary expertise to handle the equipment, tools, and materials required to vent a gas furnace, don't hesitate to hire a professional.

Step 1 - Know Which Vent Type You Have

When venting your gas furnace, you need to know the different kinds of vents that can be installed. The first is the direct vent, which directly throws all the air into the atmosphere. Most old gas furnaces use the direct mechanism.

Modern furnaces use Type B pipes, which are more environmentally safe. They are also authorized for use by regulatory bodies and insurance companies.

Step 2 - Take Measurements

Measure the distance from the furnace’s vent to the chimney. Make note of any odd obstacles, twists, or turns that may obscure the path between the vent and chimney.

These measurements and observations will ensure that you buy enough materials, such as piping and elbow joints, when attempting to construct a vent pipe for your furnace.

The diameter of the vent pipe should always be larger than that of the gas furnace flue, ensuring that no gas escapes from the pipe. Gas furnaces usually come with their own specifications, try and adhere to them even if building the vent on your own.

Step 3 - Crimp Your Pipes

Crimping allows the pipe to connect to the next without any trouble, and overlapping the piping at each of these joints prevents any gas leakage.

If your pipes have crimped ends, make sure those ends are always facing the chimney as you assemble the pieces.

Step 4 - Connect the Pipes

Attach your first piece of pipe to the furnace and ensure there are no gaps or leaks for toxins to escape. Work your way up toward the chimney, creating the vent by connecting pipes using elbow joints.

Using at least four sheet metal screws, connect the pipes together and screw them in tight. If the length of the pipe is more than 5 feet, you may need to support the weight of the pipe using galvanized hangar straps.

Step 5 - Seal the Deal

It is important to ensure that there is complete air-tightness at all the joints and sections. Use a heated silicone caulk to seal all joints and seams along the metal pipe, the gas furnace, and the chimney.