x 25-in. Return grilles are the best choice for a five-ton system in order to deliver 2,000 cfm back to the blower without causing the return to hemorrhage.

What size duct do I need for a 5 ton unit?

Using this approach, two 20-in. x 25-in. return grilles will be the right choice for a five-ton HVAC system in order to actually deliver 2,000 cfm back to the blower without causing the return to hemorrhage.

How big should my return air duct be?

Generally, if you are using a Duct Sizing Chart or calculator (such as the Trane Ductulator), size the re- turn ducts for 0.05 inches/100 ft (0.40 Pa/m) based on the expected airflow through that return air duct. The total sum of air from all the returns should be at least 250 CFM/nominal ton (33 l/s per-kW).

How much return air do I need per ton?

You can never have to much return air, as a HVAC contractor you want no less than 144 square inches per ton. Regarding the 3.5 TON VS 4 TON The average square foot per Ton is 400 so say the house is 1600 SQFT a 4 TON unit should work great.

How many CFM is a 5 ton unit?

A 5-ton system should have have 2,000 cfm, a 6-ton system should have 2,400 cfm, and so on and son. Measuring how much airflow measurements deviate from that math is a quick way to diagnose airflow issues in a residential duct system.

How many CFM is a ton of return?

The airflow is measured in cubic feet per minute (CFM). 350 to 400 CFM per ton of cooling is required for proper air conditioning system operation.

Can a return air duct be too big?

Can an air return be too big? No, an air return cannot be too big, except in extreme cases where a closed room is temporarily under negative air pressure. Return vents maintain air pressure, filter out debris, and are critical to the efficient operation of any HVAC system.

Should return duct be same size as supply?

Yes, return ducts are usually larger than supply ducts to ensure that air within the home is balanced. There are generally more supply vents in the system creating the need for return vents to be larger.

How many returns do I need for a 4 ton unit?

(Example: 4 (ton unit) x 144 square inches = 576 squared. The square root of 576 is 24. Therefore, your return air duct and grill size will be 24 by 24 inches.)

How many CFM does a 6 inch duct have?

“For example, most techs will tell you that a 6” duct will provide about 100 CFM.”

How do I know what size flex duct I need?

Measure the length and width of the room where the flex duct will be supplying the air. Multiply the length and width together to get the square footage of the room. For example, a 10-by-10 room will be 100 square feet.

Can flex duct be used for return air?

Flex duct is widely used for return air in commercial air conditioning systems. Flex duct is able to withstand a certain negative pressure of return air. When installed properly, a flex duct is a reliable and convenient ductwork solution. Flex duct often gets a bad rep because of airflow issues.

How many CFM is a 4 inch duct?

Reviewing the chart, a 4” pipe will convey 395 CFM at 4500 FPM. This means that a 4” pick-up on a machine will use 395 CFM from the filtering system; or, if you know that a machine will require approximately 400 CFM to remove the waste, you should use a 4” pipe for that purpose.

What size ductwork do I need for a 3 ton unit?

Multiply the tonnage, 3.5, by the total BTU per ton and this will give you the total BTU rating. Multiply 6 x 42 to determine the duct size of 252 square inches The clear are of the duct must be at least 252 square inches This measurement also includes the opening in the floor at the bottom of the return.