repair person opening ac duct

Everyone wants an effective HVAC system, but not everyone has a ton of extra room to install one. Window air conditioners and standing air conditioners can be bulky and annoying. Old-school radiators make strange noises, take up space, and can even be dangerous for children. If you have a 2×4 wall cavity, then you have enough space to learn how to run HVAC duct in 2×4 wall that can make your home comfortable in all types of weather. Wall air conditioners are great for people that don’t have windows that will work for an air conditioning unit made for windows.

Follow this guide to understand how to run an HVAC duct into a 2×4 wall cavity so that you can install a wall air conditioner.

What is an HVAC Duct?

An HVAC duct is a cavity in the wall the leads to the outdoors using metal tubes. These can run all through houses and apartment buildings, so every area of your space can be comfortable even if it isn’t near a window.

Installing one of these should be done by a professional as it involves a lot of knowledge on ductwork and a great deal of construction. The ductwork needs to be placed between studs and joints in the wall. It needs to have a clear path through the walls without being interrupted by vital foundations. This gets complicated which is why it’s best to leave it up to a professional.

How Do HVAC Ducts Work?

HVAC systems use heating and cooling coils to adjust the temperature of the air. Then using a type of fan, it blows the desired air into the living spaces. As this happens, the undesirable air is pushed into the ductwork vents to make your space comfortable no matter what season it is.

Parts of the HVAC system

These are the main parts that make up your ductwork for the HVAC system.


how to run hvac duct in 2x4 wall
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The ducts have one large main trunk that has all the other pipes shooting off it to direct the cool or warm air where it needs to go.

The trunks and pipes of these systems are made of galvanized steel usually. Then there is flex piping ductwork that is usually made of aluminum and is more flexible so it can be fitted into corners and tight spaces throughout your walls.

Trunks and pipes are just the beginning of the kinds of ductwork in your home. There are stacks in addition to the trunks and pipes and many more types of ducts that function differently to provide air to all the different parts of the home or building.

Duct Transitions

Duct transitions are the parts of the ductwork that allow the pipes to flow throughout your home and enter all the desired spaces.

Not all houses use the same layout, so there isn’t one perfect ductwork system for every home. A professional can determine the best path for the ductwork and utilize different duct transitions to accomplish this.

Duct trunks and pipes are connected with take-offs, turning vanes, cleats, and other specialized connectors and can end with angled boots to stop air from escaping.


Flues are the part of the system located half inside and half outside of the house or building. These need to be well-insulated so no air can seep in through the cracks in the sides. Another reason it is so important to use a professional is that insulation is vital to making the HVAC system work as it should.


A plenum is a giant box that stores air and connects to all the ductwork. Most systems have two of these boxes, one that pushes the desired air out into the building, and a return plenum that takes in the undesired air.

The heating or cooling coils send the air into these boxes for temporary storage until the air is pushed out into the home. When this air is pushed out, the air that was in the room is pushed into the air vents, like a dryer vent, and goes to the return plenum to be run through the coils or let outside.

Drain Pans

Drain pans are important because HVAC systems use water to cool or heat the air, depending on the system. They catch excess water and condensation so that it doesn’t leak through walls and damage the ductwork system.

Drain Lines

The drain lines are what direct the excess water to the drain pan. They are located within the pipes and lead to the drain pans. Without these, the water would seep into your wall resulting in mold, mildew, and other health risks. This is one of the reasons properly installed ductwork is so important to a healthy home.

Refrigerant Lines

The refrigerant lines draw refrigerant into the compressors, which are how the HVAC system can cool or heat the air. These refrigerant lines are the same ones found in refrigerators.

Air Handler

The air handler is where the heating and cooling coils are located along with the blower fan. This moves the air throughout the ductwork pushing it into different areas and dispersing the desired air.

Most air handlers also contain a filter so that the air you breathe is purified and doesn’t contain any harmful toxins.

Bottom Line

Running an HVAC in a 2×4 wall cavity is quite an undertaking but will result in a more comfortable home with ideal temperatures for every season. A 2×4 wall is a great location for HVAC ductwork.


How Often Should I Replace Ductwork?

Ductwork and HVAC systems can last longer when properly maintained. Make sure to change filters every three months at the least. Doing this regularly, means your system and ductwork should last 10-15 years depending on the quality of the materials.

Can I Do It Myself?

If you have experience with construction and HVAC, you could take on this project. But we recommend hiring a professional to ensure insulation and installation are done properly so you can enjoy your HVAC for a long time.