It s a 1600 cfm system with 200 cfm of outside air 200 1600 12 5 of outside air.
Return filter grille cfm chart.
Return a return draws air into a return duct system with negative pressure compared to the space usually via a fixed grille but.
First let s define some terms.
Particle diameter strainers and filters mesh size vs.
Return filter grille specification chart.
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.
Table 4 2 return air duct installation sizes based on 05 inches of pressure drop per 100 ft round duct rectangular duct cfm dia.
The return air grill will also usually have a filter inside it to trap particulate matter and other contaminants in the atmosphere of your dwelling.
Particle diameter opening size.
Air intakes and outlets ventilation systems air intakes and outlets rules of thumbs.
D minus 2 3 4 d heavy guage steel construction concealed hinges equipped with filter retainers uses 1 nominal disposable filters finish.
Note also the return air grille sizing formula at the top of the chart.
Ventilation systems for ventilation and air handling air change rates ducts and pressure drops charts and diagrams and more.
The most common place you will find furnace filters are either in the unit or in the return air ductwork right next to the unit.
Then subtract the percent of outside air from each return air grille airflow in the system as calculated above to find the required adjusted return airflow.
You determine a return grille pressure zone required 340 cfm of return.
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.
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.
This comes in handy if your furnace is in an attic or otherwise hard to access area.
Situations may arise where you want or need to install the filter at the return air grille.
A return air grill will also look similar to the supply side grill and can only be differentiated by the flow of the air.
For the same 2 5 ton system with a filter grille the grille size would need to be what size asked rick we usually use a 20 x 20 for 2 5 ton said the tech 20 x 20 x 2 800 800 cfm well that s big enough for a 2 ton but a 20 x 25 may be a better choice.
