Ductwork installation can be a bit of a mystery to some people. We’re here to clear it up. Use our guide before you get started. We cover common HVAC terms and explain the installation process.

A Guide to Ductwork Installation

Most homeowners, especially new homeowners, can't afford to hire someone for ductwork installation. The going rate for someone to install your ductwork for you is about $60 an hour. Taking on a duct installation project DIY-style can save you quite a bit of cash.

Develop a Duct Plan

Ductwork Installation Initial Process with all materials set-up at a Mechanical Room

Image: CC by 2.0, MTA Capital Construction Mega Projects, via Flickr

A duct plan is an official outline for the entire duct system. Professionals use design software to lay out a plan that works well for the current structure of the home. You can invest in this software or work with a designer through freelance or contract agreement.

A duct plan should have the following:

  • Size of the ducts
  • Size for the holes
  • Location of the ducts
  • Location of the registers
  • Identify the return duct system

These vital points will set you up for success with any ductwork installation. Always be sure that your duct plan is as specific as possible.

You can take special precautions to ensure you won’t run into any issues during the installation process now. These special precautions can include things like running your ductwork center to the floor joists. Or, planning for at least 3 inches of wall clearance. There is no such thing as a duct plan with too much detail.

You’ll also want to use some HVAC best practices such as allowing a basement to have its own ductwork system. A basement usually needs its own return and supply duct system. The branches for the basement can connect with small strips of flexible duct and return to the primary duct system. But allowing the basement to have its own mapping is important.

Mark the areas on your duct plan where you want to use flexible duct for your connections. The flexible duct can hold well for years. But if you use too much in one area, it will wear out quickly.

You can also use the duct plan to make a note of where you have dropped ceilings or have other obstacles with building design such as pipes. Every home or office building will come with some set of design obstacles to overcome.

Start the Rough-In Stage

Workers inside Ductwork during the Renovation of the White House for Ductwork Installation

Image: Public Domain US, The U.S. National Archives, Flickr

The rough-in stage is the point where you begin to carve out the holes for the ductwork. You'll need a few tools, specifically a precision saw and at least 2 different sheet metal snips.

Exact cuts aren’t vital here. After you complete the installation of the duct system, you'll need to put up drywall and paint. You should worry about your cuts for a proper fit, rather than how they look. Doing this part of the job correctly will job with the right tools.

As you carve out your hole, be sure to measure regularly. You don’t want to stray from your duct plan.

By now you should start seeing the end-goal beginning to take shape. You don’t have any ducts up yet, but you should have everything opened up for a quick installation.

Remember that as you cut into the floor and walls for your holes, you’ll need to mark the places that are for supply registers and the holes for return air. The return air system is essential to the installation process but is one of the last concerns. Continue making room for the return air system and know that you’ll visit this part of the installation last.

Ideally, you'll have the holes that will be for returning air cut into the bottom plate of a wall. The best way to direct returning air is through the subfloor. You'll also want to use a metal frame for installation. The proper term for this metal frame is “plaster frame.” The plaster frame makes it easier to cut through drywall with precision.

Setting Stage

Men Working on a Rough-In Stage Ductwork Installation with all materials set-up at a Mechanical Room

Image: CC by 2.0, MTA Capital Construction Mega Projects, via Flickr

Another step of the rough-in stage is the setting. You want to set everything into place, including:

  • The Furnace
  • The air handler
  • The evaporator coils

Finally, you want to install the plenum. A plenum is the metal box that connects a supply duct to a furnace when your home doesn't have a central air conditioning system.

To install the plenum, you’ll want to insert them with a collar into the place where your ducts will connect. These act as a type of exterior cuff that will protect each joint in the ductwork system.

The Plenum and Collar

To fit a plenum and the collar together, you'll need to follow these steps:

  1. Cut a hole into the plenum near the fittings
  2. Insert the tab of the collar into the plenum’s hole
  3. Bend the tabs
  4. Tighten with metal screws

These 4 easy steps will help secure the primary aspects of your ductwork installation. The collars and plenum serve to deliver quality support and will keep your system bound together.

Main Trunk Line Installation

Workers installing a HVAC ductwork in the Cannon Building's west wing construction zone for Ductwork Installation

Image: Public Domain US, USCapitol, Flickr

Whether you’re working with square or round ductwork, you will use an installation method that requires you to connect multiple pieces. This is the step in the process when the project begins actually to look like ductwork.

If you’re working with round ductwork, you’ll want to set up your main trunk line like a zipper. Some people prefer round ductwork because you fold over the same section, rather than the interlocking you must do with square ductwork. You can work the seam together and close the edges with dampener clips.

But, square ductwork is a little different. With square duct, you'll want to assemble the main trunk line and mount it through the plenum collars you put in earlier. Square ducts rely on tabs and connections to interlock the pieces. The square ductwork uses 2 different connection methods. The round ductwork connects purely through dampener rings.

The Process

A square ductwork system uses an “S” or “drives” connection. In “S” systems a piece of metal folds over another piece. This folding results in a slot that lets a different duct slide into place.

A drives connection uses pieces of metal that fold onto themselves. These folded pieces also multiple ducts to slide together and lock on the sides. For drives, you must bend each tab, and you go through the system. It may seem like more work, but it's more secure than opting out of this step.

For square ductwork, you'll need to support the weight of the hanging ducts evenly. Many contractors or HVAC technicians feel confident when they secure the hanging ducts every 6 to 8 feet. Using suspending metal hangers, the installation process moves very quickly. You still want to stop and measure once in a while. Stick to your duct plan.

During the main trunk line installation, you will also install the end cap. An end cap is the final piece of the supply duct system.

Branch Supply Duct Installation

temporary plastic air duct leading out from a location where asbestos abatement is taking place for Ductwork Installation

Image: CC by A 2.0, Kurt Nordstrom, via Wikipedia Commons

After the main trunk link is in, you can start focusing on the branch supply ducts on ductwork installation. These ducts usually use round ductwork or pipes that attach onto the takeoff from the main duct. They do exactly what they sound like should do. They “branch” out from the main line to reach other rooms or different areas of the building.

Unlike the main trunk line which can be difficult to set up, the branch supply duct installation process snaps together. The branches connect with a simple joint that only needs 3 screws. Every 6 to 8 feet you do need a support bracket to help keep the system safe.

You must also cut each branch to length. For this step, you must reference your duct plan. After you cut each branch to the appropriate length, you need an elbow boot fitting to take the round brand supply duct back to a square duct at the registers.

The “boot” installs into the subfloor with nails that sit flush to the surface of the floor. This section acts as a large joint for each branch and provides stability to your duct system.

Return Ducts and Why You Need Them

Pilot Plant worker who cuts insulation for placement around the Munitions Demilitarization Building Filter Bank ducts for Ductwork Installation

Image: CC by 2.0, PEO ACWA, via Flickr

There are 3 things you need to build your return air system on ductwork installation:

  • A slot in the metal elbow for an air filter
  • A collar
  • A duct line

These pieces will work together to make up the start of your return air system. The main duct system has a cap on one end but is still open on the other. This is going to use the one-ended main duct system to direct airflow.

Moreover, it has a similar setup but uses design to inlet the furnace air. Then, it connects to the branch ducts and eventually back to the main trunk line. The return ducts often meet the branch ducts at the empty spaces between floor joists with panning.

The Set-up

Men Doing Ductwork Installation Along East Service Corridor

Image: CC by 2.0, MTA Capital Construction Mega Projects, via Flickr

Panning is pieces of metal that attach to joists and close the duct. This is important as it helps direct air flow. When panning attaches to a supply duct on one side, it must attach to the main duct on the opposite side.

Panning, and the return air duct system work to establish an air flow that is beneficial for the building.

The last step in ductwork installation is closing off the joists with panning. You must ensure that all of your return air holes are duct into the subfloor for easy panning installation. Afterward, you can cover the system in drywall and paint. Then no one will be the wiser. Also, the only difference is the amount of control over the heat and air in their building.

Hence, many people don't realize that the air grilles on their floors, or walls are the openings to these complex systems.

Assessing Your Ductwork Installation Ability 

Although the process sounds complicated when you look at it from start to finish, the steps are simple. Ultimately, you will have to assess your abilities and how comfortable you feel working with this type of job. But keep in mind that it is vital to start any ductwork job with the right tools, and a detailed duct plan.


Featured Image: CC by 2.0, LouisvilleUSACE, via Flickr