How to Connect Heating Ducts

What You'll Need
Start collar
Heating ducts
Duct tape
Metal clamps

You need good heating ducts in your home to effectively distribute warm air from the furnace around the house. If you’re replacing ducts or adding new ones you can easily do the work yourself. Although it's not complex, it can be a tricky job and you need to have the right size of heating ducts. If they are too small or too big and you won’t be heating the room in the most efficient way.

Step 1 - The Right Ducts

Before you buy the heating ducts you have to figure out what size heating ducts you need for the different rooms. Go on the basis of needing one cubic foot per minute of air, or CFM, for each square foot of the room.

At the hardware store, calculate what diameter of heating ducts you need for the different rooms. They will all come in standard lengths of 25 feet. If you go for a duct with a 4 inch diameter it can carry 30 CFM, with 8 inch carrying 230 CFM, 12 inch heating ducts carrying 680 CFM and 14 inch heating ducts carrying 1000 CFM. You can also purchase other diameters offering CFMs in between those figures.

Step 2 - Cutting

The first thing you’ll need to do is assemble the duct work to go from the furnace to the rooms. To do this you’ll need to cut the heating ducts. Use a pair of scissors for this. When you have to put pieces together you’ll need to fold back the insulation on the heating ducts as well as the jacket then put a 4 inch metal sleeve on the heating ducts to join them. To hold the heating ducts in place on the metal sleeve use duct tape, wrapping it twice around each piece. Add a pair of clamps on each side for more support then cover them with the jacket and the insulation for the best look and least heat loss. You should also run duct tape around all of the seams.

Step 3 - Installation

As the heating ducts go inside the walls of the house you’ll need to start by installing the vertical sections within the walls followed by the horizontal sections. The initial piece will be connected to a collar, letting it connect to a horizontal piece. Pull back the insulation and then put on the collar. Wrap duct tape around it and then use a metal clamp over that before returning the jacket and the insulation.

Step 4 - Support

The home heating ducts will have to be supported. There shouldn’t be a sag of more than 1.2 inch over 5 feet. You can use wire wrapped around the heating ducts and attached to the joists or rafters. There are also special metal hangers available.

Have the holes cut in the floors of the rooms and fit metal collars inside them. Attach the heating ducts to these with duct tape and cover the holes with grilles of the correct size.