What Size Supply Duct for a 5 Ton Unit?

When installing a 5-ton air conditioning unit, one of the most crucial aspects to consider is the size of the supply duct. The right duct size ensures efficient airflow, optimal cooling performance, and prevents unnecessary energy consumption. In this article, we will delve into the factors that influence duct size, the standard sizes available, and how to determine the best fit for your 5-ton unit.

Understanding Duct Size

Duct size is typically measured in inches and is denoted by a two-digit number, such as 10×6 or 12×8. The first digit represents the width of the duct, while the second digit represents the height. The size of the duct is crucial because it determines the airflow capacity and the overall efficiency of the system.

Factors Influencing Duct Size

Several factors influence the duct size for a 5-ton unit, including:

Room size and layout
Number of supply registers
Return air duct size
Length of the ductwork
Friction loss

Room size and layout play a significant role in determining the duct size. Larger rooms or rooms with high ceilings may require larger ducts to ensure adequate airflow. The number of supply registers also affects the duct size, as more registers mean more air needs to be distributed. Additionally, the return air duct size should be proportional to the supply duct size to maintain proper airflow balance.

Standard Duct Sizes for a 5-Ton Unit

Standard duct sizes for a 5-ton unit typically range from 10×6 to 12×8 inches. However, the ideal size may vary depending on the specific factors mentioned earlier. Here is a table showcasing the standard duct sizes and their corresponding airflow capacities:

Duct Size	AFUE (Airflow per Unit of Energy)
10×6	300-400 CFM (Cubic Feet per Minute)
10×8	400-500 CFM
12×6	400-500 CFM
12×8	500-600 CFM

As you can see, the 12×8 duct size offers the highest airflow capacity, making it a suitable choice for larger rooms or spaces with high ceilings. However, it is essential to consider the other factors mentioned earlier to determine the best fit for your specific situation.

Calculating Duct Size

Calculating the duct size for a 5-ton unit involves several steps. Here’s a simplified process to help you determine the appropriate duct size:

Determine the total square footage of the space to be cooled.
Calculate the required airflow per square foot, which is typically between 20-30 CFM.
Multiply the total square footage by the required airflow to determine the total airflow needed.
Divide the total airflow by the airflow capacity of the standard duct sizes to find the most suitable duct size.

For example, if you have a 1,000-square-foot room and want to achieve an airflow of 25 CFM per square foot, you would need a total airflow of 25,000 CFM. Dividing this by the airflow capacities in the table above, you would find that a 12×8 duct size is the most suitable option.

Conclusion

Choosing the right supply duct size for a 5-ton unit is crucial for ensuring optimal cooling performance and energy efficiency. By considering factors such as room size, layout, and airflow requirements, you can determine the most suitable duct size for your specific situation. Always consult with a professional HVAC contractor to ensure accurate calculations and proper installation.