How to Install a Gas Furnace Chimney

What You'll Need
Drill/Drill bits/Core bit
Duct materials
Tape measure
4-inch galvanized sheet metal ducting
4-inch galvanized elbows
Sheet metal screws
Tin snips
Pipe crimper
Galvanized hanger strap
High-temperature silicone caulk/Caulk gun
Gas leak detector/Carbon monoxide detector

A gas furnace chimney plays an important role in the functioning of a gas furnace. In fact, both the chimney and furnace go hand-in-glove and function as a system. The chimney’s role involves driving the system by ensuring that the flue gases are exhausted from the stove. It also, at the same time, pulls air into the stove. Most gas furnace chimneys are made out of sheet metal pipes that are galvanized. Installing a gas furnace chimney is a relatively easy DIY project, if you have the right tools and some know-how.

Step 1 – Preliminary Checks

The gas to the old unit should be turned off before you start doing anything. Once this is done, detach the old unit that you used for heating taking care not to cause any damage. Make sure you address any issues you have with your current duct work before you proceed. Ensure that the duct work is in good shape; else your new heater may not work properly. You also need to make sure your furnace is aligned with the duct work and gas pipes that already exist in your house. 

Step 2 – Attach the Heater and the Furnace

Next, hook up your heater to all the ducts. Care has to be done while doing this so as to make sure that your entire house gets heated evenly. You can first connect the plenum and ensure that the duct is properly attached with the help of a clamp. Then, hook up the new furnace to the gas line and turn the gas on. Check the instructions provided with your furnace to see if any construction is required before the installation process. Also make sure that there are no leaks with the help of a gas leak detector.

Step 3 – Install the Gas Furnace Vent

Measure the distance between the flue discharge on the furnace to the chimney, and accordingly buy a galvanized sheet metal duct and elbows. Then, drill a 4¼-inch hole into your chimney, and pitch your furnace venting towards your chimney at about ¼-inch per foot. Ensure that the hole is cored high enough to accommodate the pitch.  

Next, you will have to install the metal ducting. This can be done by connecting the pieces together. Simply insert the crimped end of one piece into the end of another piece that is non-crimped. Use metal screws to secure the connection. Adjust the metal ducting as needed, and use elbows to make the necessary turns and twists to get from the furnace to the chimney. Finally, with the help of a hanger strap that is galvanized ensure that you support your venting. Use high silicone caulk to seal the chimney to the furnace venting. 

Step 4 – Check for Leaks

Once everything is done fire up your chimney to make sure that there are no leaks. You can do this with a carbon monoxide detector.