Air Conditioning Duct Size

Flex duct 05 on most metal duct calculator round metal pipe 06 on most metal duct calculators.

Air conditioning duct size.

A rule of thumb says ducts should carry 400 cubic feet per minute cfm of air for every one ton of cooling. The following duct sizes are based on a fraction drop of 10 inches per 100 feet of lineal duct. Duct sizing for air conditioning is a complex process using one of three methodologies. 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.

Larger volumes or higher static pressures should be dealt with on an individual job basis. So if you have a two ton system you need ductwork that will carry 800 cfm. This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications.