Hvac Return Duct Size

An hvac return air can be in the floor but they work much better on walls up about 7 feet.

Hvac return duct size.

Click or tap here to get free bids in hours from local hvac companies to have new return air ducts installed in your home. Visual inspection for prior attempts to improve return air such as holes cut into an existing return air duct or worse openings cut to admit more makeup air into the air handler from an un conditioned space such as an attic or crawl area. You need close to 600 sq. Use the following formulas.

Calculate the size of your ducts vents by multiplying the length by the width. Round ducting comes in standard sizes ranging from 4 9 inches in diameter to just over 41 inches in diameter with sizing also depending on airflow needs per cubic foot per minute and velocity. We like to have 200 ton. Calculate the return duct size based on the air conditioner s size and the type of duct you are using.

For example if the vents are 5 by 10 inches the total cmf for the vents is 50 cmf per vent. There usually are fewer return vents but they are much larger. Your return ducts are just right but the return grills are way to small. Step 5 divide the cmf per vent by the total amount of cmf for your furnace.

4 tons x 144 square inches return air duct in square inches. Nominal size in x in approximately capacity cfm 10 x 4. 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. A typical supply vent is 4 by 10 to 12 inches and a typical return vent is 16 by 20 inches or larger.

Most technicians are skeptical about these numbers especially on the return air side of the system. Design cfm 4 cfm 6 cfm 8 cfm 10 cfm 12 60 6x4 60 4x6 90 4x8 120 4x10 150 4x12 90 8x4 110 6x6 160 6x8 215 6x10 270 6x12 120 10x4 160 8x6 230 8x8 310 8x10 400 8x12 150 12x4 215 10x6 310 10x8 430 10x10 550 10x12 180 14x4 270 12x6 400 12x8 550 12x10 680 12x12 210 16x4 320 14x6 490 14x8 670 14x10 800 14x12 240 18x4 375 16x6 580 16x8 800 16x10 950 16x12 270 20x4 430 18x6 670 18x8 930 18x10 1100. A mismatch in return air inlet grille or duct size will reduce the system s effectiveness.