Return Grille Size Cfm

It s a 1600 cfm system with 200 cfm of outside air 200 1600 12 5 of outside air.

Return grille size cfm. Always round up and we have a tonnage value of 2 5. First let s define some terms. You determine a return grille pressure zone required 340 cfm of return. A return air grill should be sized for an air speed of 300 500 fpm feet per minute.

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. For example a 5 ton unit should have a 30x36 grille 2 18x30 filters. Ventilation systems for ventilation and air handling air change rates ducts and pressure drops charts and diagrams and more. Return a return draws air into a return duct system with negative pressure compared to the space usually via a fixed grille but.

Wxh wxh wxh wxh wxh wxh wxh wxh 80 6x6 7x5 9x4 90 7x6 8x5 10x4 100 7 8x6 9x5 11x4 125 7x7 9x6 11x5 13x4 150 8x7 9x6 12x5 15x4 175 8 8x8 9x7 10x6 13x5 17x4. So if your furnace puts out 800 cfm you need 400 square inches of filter grille area. 4 ton unit x 144 square inches 576 squared. Air intakes and outlets ventilation systems air intakes and outlets rules of thumbs.

You may round this number off to 300 cfm. 340 cfm of return air x 87 5 298 cfm. Particle diameter strainers and filters mesh size vs. Table 4 2 return air duct installation sizes based on 05 inches of pressure drop per 100 ft round duct rectangular duct cfm dia.

Therefore your return air duct and grill size will be 24 by 24 inches. In order to determine the size of the tonnage you have simply divide 980 by 400 cfm per ton. The square root of 576 is 24. 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.

Return air should be sized at 200 square inches per ton according to airmate and other filter. Calculate the square root of the total. Most technicians are skeptical about these numbers especially on the return air side of the system. Proper sizing and orientation of grilles registers and diffusers may seem like such a simple thing but it s an area where confusion and mistakes are commonly made.

400 fpm is the median air speed for this calculation. For proper operation plan on 2 cfm per square inch of filter grille area. Particle diameter opening size.