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.

Why Is My Air Conditioner Not Blowing Cold Air?

Not getting cold air on a hot summer afternoon is one of the most common air conditioning challenges. It happens at the most unexpected times, and it can be a precursor to a much bigger AC problem. Therefore, it should not be ignored. Better yet, you should strive to prevent it from happening in the first place. If it does happen, you need an urgent solution that is inexpensive and effective. While it’s possible to fix AC not blowing cold air by yourself, it’s always recommended to consult with an HVAC technician. But first, let’s first look into what’s making the air conditioner struggle to blow cold air. 

Reasons Why the Air Conditioner Is Not Blowing Cold Air

There are many reasons why your AC is not blowing cold air,  but there are a few basic situations that lead to this problem. These are: the AC is running but not cooling the house, the AC is running but blowing hot air, or the AC is not running at all.

Scenario 1: The AC Is Running but Not Cooling the House

For air conditioning units that contain an outdoor unit, this scenario occurs when the unit is blocked or clogged. Since the unit is sucking air from the sides, it tends to suck up the surrounding materials. This is what leads to blockage. Subsequently, the clog prevents the condenser fan from drawing air into the condenser, pulling heat from the interior. This process is essential and works to lower the temperature of the air circulating in the house.

How To Fix This:

In this scenario, the condenser is usually clogged with dirt, leaves, or debris. As you might have guessed, the obvious solution is cleaning. Mild dirt and debris can easily be cleaned with flowing water and a hose. First, switch off the power supply from the switch located near the condenser. Then proceed to spray water from the inside out until the condenser fins are free of the clogging material.

Scenario 2: The AC Is Running but Blowing Hot Air

The primary function of an air conditioning unit is to regulate the indoor air temperature of the room. In most cases, this regulation involves cooling indoor air when the temperature is too high. It gets to a point when the AC blows hot or warm air instead of cold, raising the heat inside your home. Unless you have a reversible air conditioner that provides heating and cooling solutions, you don’t want this to happen. But when it does, there are several reasons. These are:

  1. Incorrect thermostat setting. A manual thermostat usually requires adjusting when there is a temperature change. When these settings aren’t toggled appropriately, it can mess up the AC cycle. 
  2. A power problem. At times, cables get unplugged, and switches get flipped. 
  3. Low refrigerant. Refrigerant is responsible for the cooling properties of your entire AC unit. When it’s low, it causes pressure in the evaporator coils to drop, thus forming ice on the coils.
  4. Dirty air filters. Air filters found on the air vents accumulate all sorts of foreign material that eventually limit airflow in the house.
  5. Blocked air registers and return vents. When there is not enough air flowing inside the house, the AC will blow in hot air.

How To Fix This:

Adjusting temperature readings and modes on the thermostat is a good place to start. Alternatively, you can switch from a manual to an automatic thermostat that will adjust itself accordingly. Also, make sure connectors and switches are turned on. Then, change the air filters regularly and keep return vents open when needed. Last, call a qualified technician to fix the refrigerant leak and inspect other causes of the AC blowing hot air. 

Scenario 3: The AC Not Running Completely

This is another cause of the AC not blowing cold air. Where this is a more uncommon scenario, it can happen for a number of reasons. Your AC might be experiencing a maintenance problem that requires inspection, or it could be a switch that’s turned off. It’s also worth noting that most of the reasons we discussed above can lead to the complete failure of the whole unit. But don’t panic.

How To Fix This:

If you have basic AC troubleshooting skills, you could solve the issue of the AC not running at all. Otherwise, you might have to contact an HVAC technician to come and inspect the problem and possibly provide a fix. All in all, the issue of AC units not supplying cold air can be easily and permanently fixed. 


Weather conditions continuously make air conditioning systems essential household appliances. Therefore, when something is not working right, it robs you of peace of mind. Consider the issue of the AC unit not blowing cold air. Situations like these require prompt action to prevent further damage. As you have seen, with the right approach, it can be fixed. More importantly, we understand that problems like these can be intimidating. That’s why we are always ready to help. Are you feeling stuck? Contact us today.