How do you know what size grille to get?

In order to determine the size of the tonnage you have, simply divide 980 by 400 CFM per ton. Doing this for this space will yield a tonnage of 2.45. Always round up and we have a tonnage value of 2.5. A return air grill should be sized for an air speed of 300-500 FPM(feet per minute).

What is the formula to calculate cfm?

CFM = (fpm * area), where fpm is the feet per minute. To find the cubic feet per minute, substitute the FPM value with the area after the area is squared.

What size should my return duct be?

In a rule of thumb sense the return duct should be the same size as all the supply ducts combined. But a rule of thumb is just an initial guide, not anything to bet your comfort on. You have to consider the length of duct and the type of duct.

How big does a transfer grille need to be?

The transfer grille sizing includes allowance for one 32″ by 1/2″ door undercut. Figure 1: Transfer grille sizing for 14″ wide grille with 80% free area, with 32″ x 3/4″ included Figure 2: Return air free area required to maintain less than 3 Pa pressure difference across door

What should the dimensions be for return grilles?

For return grilles, we state the dimension parallel (running the same direction as) with the louvers first and then the perpendicular dimension second.

How big does a gas grill filter need to be?

Usually two grills 20″ X 25″ each would be used. The second formula works in all residential applications. Using 2.00 cfm per square inch the velocity of air across the filter will not exceed 300 fpm in 1 through 5 ton units. In applications of limited space, the disposable filter may be located in the return duct.

How big of a space do you need for return air grill?

So, to solve the problem of the correct size return air grill an example will lead you to the solution. Let’s say you live in a 1400 sq ft space and the ceilings are 7 ft high. The total air volume of this space is 9800sq ft.

For return grilles, we state the dimension parallel (running the same direction as) with the louvers first and then the perpendicular dimension second.

The transfer grille sizing includes allowance for one 32″ by 1/2″ door undercut. Figure 1: Transfer grille sizing for 14″ wide grille with 80% free area, with 32″ x 3/4″ included Figure 2: Return air free area required to maintain less than 3 Pa pressure difference across door

How to calculate the size of a filter Grill?

To calculate the filter grill size, divide the airflow, (CFM), by 2. 1200 / 2 = 600 square inches One filter grill or the total area of all grills must equal at least 600 square inches of area to adequately supply the system with the air needed to operate. 1 ton of cooling = 12,000 BTU 1 ton of cooling = 400 CFM (approximate)

So, to solve the problem of the correct size return air grill an example will lead you to the solution. Let’s say you live in a 1400 sq ft space and the ceilings are 7 ft high. The total air volume of this space is 9800sq ft.