How Does an Air Duct System Work?

How Does An Air Duct System Work

HVAC ducts and air vents are hidden components of your HVAC system, and they are responsible for ensuring adequate air circulation in your home. The hidden HVAC ductwork may malfunction, causing excess dust, uneven room temperatures, high electricity bills, and other air duct issues.

While some homeowners may keep up with regular HVAC maintenance and even air duct cleaning, they may not know the air duct system exists or how it works.

So, what is HVAC ductwork, and how does the air duct system work?

What is HVAC Ductwork? 

Air ducts or AC ducts are the collections of conduits responsible for supplying cold or warm air to cool and heat each room. The air ducts connect to the HVAC unit, which filters and heats or cools the air before sending it off to your rooms.

Therefore, HVAC ductwork installation is a vital component of your HVAC system. The air ducts reduce the strain on your HVAC equipment, prolonging its life and saving you money in energy costs. Proper air duct cleaning ensures fewer dust particles and eliminates excessive allergens and germs floating in the air.

If you are experiencing problems with your HVAC unit, it could be time to have an air duct repair or replacement. To understand why air duct replacement and repair may be necessary, let’s look at how the hidden air ducts work.

How Do Air Duct Systems Work? 

To understand how the HVAC ductwork functions, let’s break down the different components of your air ducts.

Pipes and Trunks 

The pipes and trunks are often the main channels connecting to an air handler and providing the conduit for warm or cooled air that flows into each room. The duct trunk is the large main trunk made of steel and flows from the furnace. On the other side, the flexible piping made of aluminum connects the trunk to each room of your home.

Duct Connectors and Specialized Transitions

During HVAC ductwork installation, the HVAC installers must connect the air ducts according to the shape of your house. The pipes and trunks mentioned above use duct connectors and specialized transitions to follow the correct paths and allow air to pass through your rooms.


The plenum is a significant component that stores air for the HVAC systems, and it is attached to various ducts. Your ductwork features the supply and the return plenums. The HVAC system fills the supply plenum with cooled or heated air sent through the ductwork. Ducts transfer the returned air to the return plenum, and the returned air flows to the outside through a flue or flows to the filtration before heading back to the system.


The flues carry the toxic gases created during the heating and cooling process and vent these gases to the outside. If the returned plenum fails to recycle the returned air, it is vented outside through the flue.

Refrigerant Lines 

The refrigerant lines occur inside the HVAC system, bringing refrigerant into the compressors. The refrigerant allows the HVAC unit to cool or heat your air.

Air Handlers

The air handler is the component where the blower fan and the filter move the air through ductwork. The air handler includes the heating and cooling coils.

Drain Pans and Lines 

Finally, the HVAC ducts consist of the drain pans responsible for draining water due to condensation in heating, cooling, and dehumidifying the air.


The HVAC ductwork plays a critical role in the air quality in your home. If your HVAC unit shows deteriorated functioning, maybe the HVAC experts should examine the ductwork and perform the necessary maintenance. Therefore, do not hesitate to contact a professional HVAC technician for proper HVAC ductwork inspection, repair, or replacement.


Frequently Asked Questions

When Should I Replace or Repair HVAC Ductwork? 

Contact HVAC technicians for air ducts inspection if you are experiencing hot and cold spots, little or no airflow from the supply vent, sudden surge of utility bills, loud noises from the HVAC system, or poor indoor air quality. The HVAC specialist will conduct air duct testing and inspection and recommend whether repair or replacement is the best option.

What are the Types of HVAC Duct Systems? 

The two main types of ductwork are flexible ductwork and rigid ductwork. The flexible round tubes feature steel wire helixes covered in flexible but durable plastic. Rigid ductwork features sheet metal or fiberglass-lined ducts.

Does Cleaning Air Ducts Make a difference? 

Air ducts get dirty over time and should be cleaned regularly. To ensure proper air duct cleaning, engage the services of a professional HVAC technician. A careless or untrained technician can damage the air ducts, leading to an increased cost of heating and cooling.