Air Conditioning Duct Size

The following duct sizes are based on a fraction drop of 10 inches per 100 feet of lineal duct.

Air conditioning duct size.

This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. Ducts should provide ample air flow to keep you comfortable without overworking your hvac system or costing you. Larger volumes or higher static pressures should be dealt with on an individual job basis. Duct sizing for air conditioning is a complex process using one of three methodologies.

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. Field duct sizing chart.