HVAC Tips / January 19, 2021

How HVAC Duct Design Factors Affect Airflow

The ductwork is an integral part of an HVAC system. The ducts deliver fresh air to targeted areas of the house and direct stale air back to the HVAC. Thus, the quality of duct design is critical to your HVAC’s performance and efficiency. Below are some factors that affect duct design and how they affect the overall airflow within the house.

What is Ductwork?

The purpose of ductwork for your HVAC system is to allow proper air distribution throughout your home. The ductwork consists of a system of ducts (the material used) that allows air to travel through heating, ventilation, and air conditioning (HVAC) equipment.

Duct work refers to when repairs or work needs to be performed on the ducts. There are typically three types of duct work; cleaning, insulating, & sealing.

When it comes to cleaning you can also include painting services from as it can allow proper air distribution.And having a good duct design is crucial to having proper airflow and typically consists of 7 components. 

HVAC Design incorporates:

  1. The shape
  2. The size
  3. Fittings
  4. The material used
  5. How it’s routed
  6. What codes are required

7 Components of a Duct Design

1. Duct Shape

The cross-sectional shape of the duct channels affects the flow of air. Ducts typically come in three shapes:

  1. Round
  2. Rectangular
  3. Oval

The cross-sectional shape affects the following:

  • The number of corners: This affects airflow speed.
  • The amount of duct material: This determines duct weight.
  • The surface area of the duct that comes in contact with the air: This determines air friction (and hence airflow speed).

Round ducts are usually the best in all these aspects. However, the technician may use a different shape, depending on other facts, such as the available space.

2. Duct Size

The duct size is the cross-sectional area of the duct. The duct size determines the volume of air that can pass through a section of the duct at any time. HVAC technicians typically express duct size (cross-sectional area) in square feet. A bigger duct delivers more air than a smaller one.

3. Duct Fittings

Duct fittings refer to the attachments or connections that are part of the duct system. Examples of fittings include:

  • Elbows used in corners
  • Connectors
  • End cups
  • Reducers for changing duct size

Fittings that protrude into the duct channel affect airflow. For example, airflow in an elbow is not as smooth as airflow over continuous sections of the duct. Thus, HVAC technicians strive to keep the fittings to the minimum number.

4. Duct Length

Duct length determines how long the air has to travel before reaching the target room (for supply ducts). The house’s size, location of the HVAC unit, and duct design all affect each duct channel’s overall length. However, long duct sizes reduce the flow rate. Thus, HVAC technicians always strive to use the shortest distance to minimize duct length.

5. Duct Material

Friction exists between the duct’s interior surface and the air flowing inside the duct. Smooth surfaces present less friction than uneven surfaces. Thus, smooth materials are better for duct construction than rougher materials.

Other factors, other than smoothness, affect material choice. For example, an ideal material should be:

  • Lightweight
  • Flexible
  • Inexpensive
  • Durable

With all these factors considers, common duct materials include galvanized steel, aluminum, and fiberglass.

6. Duct Routing

Duct routing refers to the specific location and direction of each duct channel. Factors that determine duct routing include:

  • Location of the ducts
  • Number of elbows
  • Location of the HVAC unit

For example, heated air is lighter than cool air. Thus, a duct system that rises is best for warm air delivery but not cold air delivery. The routing also determines the number of corners or elbows, which affect airflow friction.

7. Duct Codes

Lastly, the government also has a say in your HVAC system, including duct design. Duct codes determine:

  • Duct sizing
  • Duct routing
  • Duct design
  • Duct leakage

The codes affect both safety and efficiency of duct systems. For example, most counties in California require pressure testing during HVAC installation or replacement. Note that the HVAC codes prescribe the minimum requirements, but there is no harm in exceeding the minimum standards. Don’t forget that these codes may change with time.

Contact Mauzy to Get Your HVAC System Installed or Cleaned Today!

Having proper heating and air conditioning installed as well as maintained air ducts is important to the air quality in your living space. We will design and install your HVAC system, including the duct system, for maximum efficiency.  Already have an HVAC system but not show why there is low airflow? Consider having your HVAC system inspected and cleaned.

 Contact us for a quote as the first step towards professional and affordable HVAC services in San Diego.

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