Cold Air Return Duct Size

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

Cold air return duct size.

A typical supply vent is 4 by 10 to 12 inches and a typical return vent is 16 by 20 inches or larger. A return draws air into a return duct system with negative pressure compared to the space usually via a fixed grille but also often called a return vent or a return intake vent or for some of you old school folks from up north the cold air return. Use the following formulas. 4 tons x 144 square inches return air duct in square inches.

Cfm 10 x 4. Your 14 x 20 return air inlet 280 sq. For instance a 2 5 ton system approximately 400 cfm per ton would require 2 14 flexible return ducts or 1 very short flexible 18 duct to move the 1000 cfm required by the 2 5 ton system. Your filter size at the actual air handler is 20 x 20 400 sq in of air return.

There usually are fewer return vents but they are much larger. This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications. Calculate the return duct size based on the air conditioner s size and the type of duct you are using. In x in approximately capacity.

The size of the filter at the air handler gives a clue about the anticipated size of the air return that equipment manufacturer expected to have. Air return intakes sizes and capacities pdf nominal size. Houses often have two or more return collecting points each with a filter which join before re entering the heating unit. Capacities of air return intakes.

An hvac return air can be in the floor but they work much better on walls up about 7 feet. Larger volumes or higher static pressures should be dealt with on an individual job basis.