Don’t Forget to Calculate Duct Liner Weight

Maybe it seems obvious – adding duct liner insulation to a duct system will increase its total weight. But that added weight is something that’s often overlooked. And many times, it’s important. Engineers and designers sometimes need to know how much an entire system will weigh when installed, for structural reasons.

So how do you calculate the weight of duct liner per square foot? It’s based on the density of the product. With a little bit of math, you can figure out the weight per square foot of duct liner, and from there, determine how much weight you’ll add to a duct system when the liner is installed.  

To calculate the weight per square foot of duct liner:

1. Determine the square footage of duct liner being installed.  For rectangular ducts, this would be the width times the height times the length of duct in feet. 
   
   (2 x W (ft) x L (ft)) + (2 x H (ft) x L (ft)) = total square footage of duct liner
   
   To covert inches to feet, divide the “inch” values by 12.
   
   (2 x W (inches) x L (ft)) + (2 x H (inches) x L (ft)) = total square footage of duct 12 inches/ft 12 inches/ft liner
   
   
2. Determine the volume of the duct liner being installed. Multiply the total square footage of duct liner in feet (Item #1) by the thickness of the insulation in feet to determine total cubic feet of duct liner installed.
   
   Total square footage of duct liner (feet) x thickness of insulation (inches)
                                                                                   12 Inches/foot
                                                           = total volume in cubic feet of duct liner 
   
   
3. Determine weight of duct liner being installed.  Multiply the total volume in cubic feet of duct liner (Item 2) x density of duct liner in pounds per cubic feet (pcf).  Contact JM to confirm density of duct liner.
   
   Total volume in cubic feet of duct liner x density in pounds per cubic feet = weight in pounds of duct liner installed
   
   
4.  Determine weight per square foot of duct liner installed.  Divide the weight in pounds of duct liner installed (Item 3) by the total square feet of duct liner installed (Item 1).  Once you have the weight of one square foot of duct liner, you can multiply that by the total number of square feet of liner planned for use in the project to determine total weight.

Example 1, 24”W x 24”H x 20-foot-long duct insulated with 1” thick Linacoustic RC

1.  To determine total square feet of duct liner installed:
   (2 x 24”/12”/ft x 20 ft) + (2 x 24”/12”/ft x 20 ft) = (2 x 2 ft x 20 ft) + (2 x 2 ft x 20 ft)
                   = 80 sq. ft +80 sq. ft. = 160 sq. ft. total duct liner installed
   
   
2. To determine volume of duct liner being installed:
   (1” thick) x 160 sq. ft (Item 1) = 0.083 feet x 160 sq. ft. = 13.33 cubic feet of duct liner installed
   12”/ft.
   
   
3. To determine total weight of duct liner installed:
   13.33 cu. ft. of duct liner (Item 2) x 1.5 lb/cu.ft (density of 1” Linacoustic RC)
               = 20 lb total duct liner installed
   
   
4. To determine weight per square foot of duct liner installed:
   20 lb total duct liner installed (Item 3)            = 0.125 pounds/sq. ft 
   160 sq. ft. total duct liner installed (Item 1)
   
   

Example 2, 20”W x 30”H x 15-foot-long duct insulated with 2” thick Linacoustic R300

1.  To determine total square feet of duct liner installed:
   (2 x 20”/12”/ft x 15 ft) + (2 x 30”/12”/ft x 15 ft) = (2 x 1.67 ft x 15 ft) + (2 x 2.5 ft x 15 ft)
           = 50.1 sq. ft + 75 sq. ft. = 125.1 sq. ft. total duct liner installed
   
   
2. To determine volume of duct liner being installed:
   (2” thick) x 125.1 sq. ft (Item 1)     = 0.167 feet x 125.1 sq. ft.  = 10.425 cubic 12”/ft feet of duct liner installed
   12”/ft 
   
   
3. To determine total weight of duct liner installed:
   10.425 cu. ft. of duct liner (Item 2) x 3.0 lb/cu.ft (density of 2” Linacoustic R300)
         = 31.275 lb total duct liner installed
   
   
4. To determine weight per square foot of duct liner installed:
   31.275 lb total duct liner installed (Item 3)      = 0.25 pounds/sq. ft 
   125.1 sq. ft. total duct liner installed (Item 1)

This helps in part to calculate the added weight for the insulated HVAC ductwork.  Remember to include the weight for hardware such as channels, supports, hangers, etc., if applicable.

Click here for more information on JM’s complete line of duct liner solutions.