HVAC Duct Parts: A Comprehensive Guide

Your HVAC system helps keep your home at a comfortable temperature year-round. But most of the ductwork is hidden within the walls of your house, making it easy to forget about—until it stops working. This guide will teach you about the different HVAC duct parts so that you know how they work, how to maintain them, and when to call a pro for repair.

What Are the Different Parts of HVAC Ducts, and How Do They Function?

An HVAC duct system comprises numerous parts, each of which plays a role in moving heated or cooled air from the central HVAC unit through the home. When properly installed with all the right parts, an HVAC duct system maintains a comfortable temperature throughout the house. Here are the various parts of HVAC ducts and why they’re essential.

1. Air Handler Unit

An air handler unit (AHU) is a large metal box that produces hot or cold air and attaches to the ductwork to move the air around the home. AHUs have heating and cooling elements, blowers, filters, and dampers. Depending on your home’s setup, the AHU might be inside or outside your home.

2. Damper

An HVAC damper is a valve or plate that helps regulate airflow from the AHU to the duct pipes. Dampers let you create different zones in your home to regulate airflow and conserve energy. For example, you might have one zone for the living areas and another zone for the bedrooms, so you’re not heating or cooling rooms you’re not actively using.

3. Duct Pipe

The duct pipes are where warm or cool air travels through the home to a register or vent in each room. Air ducts are typically installed in the house during construction but can often be fitted retroactively in older homes built with radiators instead of central heating and air.

4. Trunk

An HVAC trunk is a duct connected directly to the furnace and/or AC unit, letting warm or cool air into the duct pipes. Trunks are typically housed in a home's basement, though they may be located in the attic if the home doesn’t have a basement.

5. Plenum

The plenum is an essential part of an HVAC duct system. Each system has two plenums: a supply plenum and a return plenum. The supply plenum draws warm or cool air from the HVAC unit and distributes it through the duct system to different rooms in the house. The return plenum takes the air from each room to the central unit, where it is filtered and sent back to the room as cold air.

6. Vent

The two main ways hot or cool air enters a room from HVAC ductwork are through a vent or register. A vent can be installed on a room's floor, wall, or ceiling to distribute air. A register vent allows you to control the airflow, while a regular vent does not.

7. Return

A vent return takes stale air from a room and channels it back to the AHU, where it can be re-heated or cooled and cycled back through the ductwork to the vents in each room.

8. Transition

An HVAC transition connects ductwork seamlessly to ensure steady airflow throughout the home. Transitions are required to connect the trunk to the duct pipes and can also be used to connect different-sized ducts.

9. Elbows

HVAC elbows join duct pipes around corners. They can be rigid, where they’re manufactured to be a certain angle, or adjustable to be used for different angles. Elbows help maintain steady airflow through an HVAC duct system.

10. Diffuser

HVAC diffusers are installed at the end of the ductwork, allowing the heated or cooled air to enter a room. While a register usually forces the air out in one direction from the floor or baseboard, a diffuser spreads the air out so it’s more evenly distributed around the room. Diffusers can increase the efficiency of an HVAC duct system.

11. Flue

A flue pipe helps vent gases from a gas-powered furnace away from combustible objects to the outside of the home. This helps prevent dangerous gases from entering your home and reduces fire risk. Flue pipes are made of insulated metal and can be run through the chimney or the home’s roof if it doesn’t have a chimney.

12. Boot

A boot is a fitting connecting the home’s ductwork to a vent or register in a room. The boot is circular on one end (connecting to the duct pipe) and rectangular on the other (connecting to the vent or register).

How to Maintain the Different Parts of HVAC Ducts

Maintaining your HVAC duct system helps it perform at its best for longer. The best way to ensure your HVAC duct system works efficiently is to schedule an annual HVAC inspection. The technician will also recommend any repairs or replacements to keep your system chugging along.

In addition, check that the vents and registers in your home are not obstructed by furniture, rugs, or anything else that could impact the airflow into a room. If the vents are blocked, the blower inside the AHU will need to work harder and can become overloaded, shortening its life.

Air duct cleaning can also help ensure your HVAC system is in tip-top shape. However, while some HVAC pros recommend regular duct cleaning, the U.S. Environmental Protection Agency (EPA) recommends only doing it as needed. If you notice mold growth, a rodent infestation, or particles blowing into the room from the HVAC vent, it’s wise to contact a professional who cleans air ducts. Otherwise, an annual inspection is all that’s needed.

Changing your filter every 90 days can keep your HVAC duct system in good working order. If you have pets or residents in the home with allergies, change your filters every one to two months instead. Your HVAC technician can recommend the proper interval to change your HVAC filter.

Cost to DIY HVAC Duct Repair vs. Hiring a Pro

Ductwork repair costs $200 to $2,100, depending on the repair needed and the type of ducts you have. On average, you can expect to pay $660 for ductwork repair when you hire a local duct installer or repair technician. DIYing duct repair can save you money on labor, but we don’t recommend it unless you know what you’re doing.

For example, changing the filter or installing a new vent could be a DIY project for a novice. But repairing a leak in the ductwork or replacing loose sections of duct pipes is best left to a professional. If you don’t fix the problem correctly, your ducts may not work efficiently and could become a health hazard.