Cold Air Return Duct Size

In x in approximately capacity.

Cold air return duct size.

Most technicians are skeptical about these numbers especially on the return air side of the system. There usually are fewer return vents but they are much larger. 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. The following duct sizes are based on a fraction drop of 10 inches per 100 feet of lineal duct.

Use the following formulas. 4 tons x 144 square inches return air duct in square inches. 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. A typical supply vent is 4 by 10 to 12 inches and a typical return vent is 16 by 20 inches or larger.

An hvac return air can be in the floor but they work much better on walls up about 7 feet. 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. Click or tap here to get free bids in hours from local hvac companies to have new return air ducts installed in your home. Your filter size at the actual air handler is 20 x 20 400 sq in of air return.

Your 14 x 20 return air inlet 280 sq. Houses often have two or more return collecting points each with a filter which join before re entering the heating unit. Size of air conditioner example. This equal friction method of duct sizing should be adequate for normal residential furnace heating and air conditioning applications.

Air return intakes sizes and capacities pdf nominal size. Cfm 10 x 4.