Ac Duct Sizing Chart

Air volume equivalent round air volume cfm 4 6 8 10 12 duct inches cfm 50 6 x 4 550 75 6 x 4 675 100 8 x 4 6 x 6 6 100 125 10 x 4 6 x 6 7 125.

Ac duct sizing chart. Duct system sizes and airflow quick chart created date. A rule of thumb says ducts should carry 400 cubic feet per minute cfm of air for every one ton of cooling. So if you have a two ton system you need ductwork that will carry 800 cfm.

Then we just add up the volume flow rates for all the branches downstream of this. To do this make sure you start at the main duct which is furthest away. Ductwork chart main duct flow rates.

Calculations are for 60 f dry air at sea level from 5 to 3000 cfm approximately standard air which is 0 075lb da ft. For the main duct g we just sum branches l and i. Most technicians are skeptical about these numbers especially on the return air side of the system.

The chart should not be used to design complete duct systems. One six inch round duct is good for about 120 cfm a six inch duct carries about 150 cfm and eight inch carries about 200 cfm of cool air. The sizing chart is designed for estimating the airflow in an average system.

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. The chart assumes the blower motor and total effective length of the duct system to be adequate for a 1 friction rate. Then we can start to size the main ducts.

To insure proper distribution of air volume dampers must be used. Rectangular duct is rounded up to the nearest 1 4 inch.