How to Install a Flue Pipe in a Furnace

What You'll Need
Work gloves
Sheet metal screws
Cordless drill
Flue glue or hi-temp silicon
Single walled galvanized steel elbows
Single walled galvanized steel pipe get the precut
Galvanized steel hanger

If you decide to purchase a gas or wood burning furnace for your home you will need to know how to install a flue pipe. Installing a flue pipe is the most important part of the installation of your new furnace. Without it, smoke and other toxic materials will build up inside the house. These toxins can have a deadly effect.

You will need to have an existing fireplace chimney to accomplish the installation. If you do not, you will need to also install a vent pipe similar to the one you have for the bathroom. Do not run your stove vent pipe through your bathroom vent pipe because the pipe for the furnace will build up heat and the methane gas is flammable.

Step 1: Measure

You will need to measure how far it is from the furnace to the old flue on the side of the chimney. If you look along the sides of your chimney, you should find a cover where there was a flue installed at a previous time. Remove the covering these are usually just a round piece of metal screwed in place.

Once you have your measurements, you will need to go to the local hardware store and purchase the correct length and diameter of pipe. Do not forget the elbows so you can turn the corners easily. The correct diameter should match the furnace on one side and the old flue on the other. If these sizes are different you can usually purchase a pipe with the two sides different to make the match.  
Step 2: Install the Pipe

Insert one of the elbows into the old flue on the chimney and attach it. You can use both the screws and cordless drill for this or just use the flue glue or hi-temp silicon. It is best to do both to maximize safety and stability. You will need to wait at least 1 hour for the glue to dry before going on.

While you wait for the adhesive to dry, attach the other elbow to one of the pre-cut pipes you purchased using the glue and the screws. Once you do that you can attach the other pipe to the other side of the elbow in the same manner. You should have an L-shaped single piece. Set this aside and allow it to dry.

Step 3: Attach the Pipe

When everything is dry, you can attach the L-shaped pipe you built to both the furnace and the chimney. You will need to use both the screws and the glue for this also.

Wait for all of the glue to dry for at least 12 hours before use.  You may wish to insulate the flue pipe next. That however is a different tutorial.