Hvac Duct Sizing

The chart assumes the blower motor and total effective length of the duct system to be adequate for a 1 friction rate.

Hvac duct sizing.

Calculate the duct size by using a duct calculator. You can also do this by checking for them online or by using a manual that is sold by distributors. In order for your forced air furnace to work properly you have to have the right sizes of duct vents in each room expelling air. Design cfm 4 cfm 6 cfm 8 cfm 10 cfm 12 60 6x4 60 4x6 90 4x8 120 4x10 150 4x12 90 8x4 110 6x6 160 6x8 215 6x10 270 6x12 120 10x4 160 8x6 230 8x8 310 8x10 400 8x12 150 12x4 215 10x6 310 10x8 430 10x10 550 10x12 180 14x4 270 12x6 400 12x8 550 12x10 680 12x12 210 16x4 320 14x6 490 14x8 670 14x10 800 14x12 240 18x4 375 16x6 580 16x8 800 16x10 950 16x12 270 20x4 430 18x6 670 18x8 930 18x10 1100.

Loss and flow in the ductwork. Air ducts friction loss diagram a major loss diagram for air ducts imperial units ranging 10 100 000 cfm. In ductwork the law of conservation of mass means a duct size can be recalculated for a new air velocity using the simple equation. This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications.

The furnace s british thermal units btus will help calculate the size it needs. For sizing the supply and return trunks select the duct size at the intersecting lines of the friction rate and the equipment cfm. While a duct sizing calculator built for a specific type of ductwork is the best possible method for sizing ducts the attached chart can be used in most single story homes with a centrally located unit and reasonable length duct runs. Installing the duct incorrectly will affect the heating capacity of the system as much as improper sizing.

If a room is 250 square feet the result will be a duct size of 8 inch round. Run the correct size from the furnace and be sure they are installed correctly. The duct vent size will depend on the size of the furnace and the size of your home so you know how many vents you need in each room. To size the branch ducts select the duct size at the intersecting lines of the friction rate and the room cfm.

Install the appropriate duct size connections. Larger volumes or higher static pressures should be dealt with on an individual. Using a duct calculator. Step 4 determine the cubic feet per minute and duct sizes for all the rooms.

Air ducts sizing air flow and required duct area. V 2 v 1 a 1 a 2 where v is velocity and a is area. Residential duct sizing guide key points to remember when using this guide the sizing chart is designed for estimating the airflow in an average system. Most technicians are skeptical about these numbers especially on the return air side of the system.

As the trunks are reduced use the total cfm of the remaining downstream branches. This will give you the size of the duct. Residential duct sizing guide the following duct sizes are based on a fraction drop of 10 inches per 100 feet of lineal duct.