Duct Surface Area Calculator
Click the "Calculate" button beside the Duct Surface Area input on the Duct Load Factors page to open this page. You must have a project open in order to open this page.
The surface area of ducts in unconditioned spaces is an important factor in determining the amount of loss or gain due to ductwork in the system.
OK Button: Saves the data on this page and returns you to the Duct Load Factors page. You must click OK to save your data on this page. It is not necessary to click the Refresh Surface Areas button before clicking OK.
Cancel Button: Discards any data you may have entered on this page, and returns you to the Duct Load Factors page.
Supply, Return: This page consists of one set of inputs for supply ducts, followed by those for return ducts. You can choose different options for supply and return if you like.
Main Options (User Defined, Get from Duct Design, ASHRAE Standard 152 and Custom): Your selection on these large radio buttons specifies how duct surface area will be determined. All of your inputs on this page are saved upon clicking the OK button, regardless of which main option you select for supply and return.
This method simply lets you directly enter the surface area.
Surface Area: Specifies the user-defined surface area that you want for the current duct load factor scenario, in square feet or square meters, depending on your project units setting.
This method makes it so the current scenario gets the duct surface area from the actual ducts you have entered for this system. The assignment of duct surface area will be made during calculations.
This method lets you find a very rough estimate of the duct surface area based on the floor area and number of returns.
Insert Below Button: Copies the "Current Calculated System Floor Area: value shown above this button into the Floor Area input.
Floor Area: Specifies the floor area to plug into the formulas shown below this input to determine the supply and return surface areas.
Keep surface area updated with system floor area (turns tracking on): Makes it so the duct surface area based on floor area is kept up to date as you enter new rooms or edit existing rooms in the system.
Number of Returns: Specifies the number of returns to plug into the formula for the return surface area. The maximum allowed number of returns is 5.
Supply Surface Area: Shows the calculated supply surface area using the following formula:
Supply Surface Area = Floor Area * 0.27
Return Surface Area: Shows the calculated return surface area using the following formula:
Return Surface Area = Floor Area * 0.05 * Number of Returns
Refresh Surface Areas Button: Optionally updates both the supply and return surface areas shown after you type in any new data. It is not necessary to click this button before clicking OK, since the surface areas will be recalculated anyway upon clicking OK.
This method lets you enter up to 10 rows of duct sizes and lengths in order to calculate total duct surface areas for supply and return. Simply select the shape and fill in either Diameter or Width and Height, then enter the Length for each size of duct that occurs in the current duct load factor scenario. The duct surface areas for each row are calculated using these formulas.
Shape: Specifies round or rectangular shape. For round ducts also fill in Diameter and Length. For rectangular ducts also fill in Width, Height and Length.
Diameter, Width and Height: Specifies the indicated dimensions of the duct, in inches. For round ducts you only need to fill in Diameter. For rectangular ducts you only need to fill in Width and Height.
Length: Specifies the length of indicated ductwork, in feet.
Total Surface Area: Shows the sum of the supply or return surface area rows. The supply and return surface areas will be copied back to the Duct Load Factors page upon clicking the OK button at the top of this page.
Refresh Custom Surface Area: Optionally updates the surface area shown after you type in any new data. It is not necessary to click this button before clicking OK, since all surface areas on the page will be recalculated anyway upon clicking OK.