What size return do I need for a 2 ton unit?

Using this rule of thumb method you would need a 20 X 20 return filter grille for a 2 ton unit rated to move 800 CFM.

What size air return do I need for a 3 ton unit?





approximately 1200 CFM

If the actual airflow is unknown, use 400 CFM for each ton of cooling. A 3-ton heat pump has approximately 1200 CFM of air flow.

How much return air do I need per ton?

2: Sizing return grilles is easy; just use the 1 sq. ft. per ton or 100 sq.in. per ton rule of thumb.

How big of a return air do I need?

You should install 1 return vent per 200-300 sq ft of basement. This is not an exact figure; it’s a ballpark estimate. For an exact figure, you will need to consult with an HVAC specialist. Example: If you have a 500 sq ft basement, you will probably need 2 cold air return vents.

How many CFM is a 12 round duct?





CFM Sizing Chart For Metal Round Ducts (50-2,000 CFM)

Duct Size (Inches) Metal Duct Airflow (CFM)
10 inches 325 CFM
12 inches 525 CFM
14 inches 750 CFM
16 inches 1,200 CFM

Can you use round duct for return air?

Yes, you can use flex ducts for your return air. However, to maximize its usefulness, it needs to conform to technical specifications such as its insulation rating, pressure checks, dust filters, duct sizing and placement, and lastly, the installation requirements.

Can return duct be too big?

No such thing as too much return. It will not take in any more air than it pushes out, thus no such thing as too big. Its hard to imagine a return that is too big ,but you want the return to have some draw to evacuate an area.

How many vents should a 2.5 ton AC unit have?

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.

Can you have too many HVAC returns?



Having several return vents (ideally one in every room, but even two or three is better than just one) creates consistent air pressure. If you have one return vent, your home is fine. Keep the doors to each room open so air can properly circulate.

How do you increase return air flow?

5 Ways to Improve Airflow in Your Home

  1. Check Vents and Registers. One of the simplest things you can do to increase airflow in your home is to check the vents and registers in each room. …
  2. Turn on Ceiling Fans. …
  3. Schedule HVAC Maintenance. …
  4. Consider Duct Cleaning. …
  5. Invest in a Ventilator.

How much return air do I need for a 4 ton?



(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 much space does a cold air return need?

6-12 inches

So how much space does an air return vent need to work properly? Home Inspection Insider explains that an air return vent needs 6-12 inches of space in front of it, and recommends that you do not put large, bulky furniture like couches and bookshelves in front of an air return vent.

How many CFM is a 2 ton unit?

How Many CFM For 1 – 6 Ton Units? ( Chart)

Unit Tonnage: CFMs Required:
1.5 Ton Unit 600 CFM
2 Ton Unit 800 CFM
2.5 Ton Unit 1,000 CFM
3 Ton Unit 1,200 CFM

What size duct do I need for 2000 CFM?



2000 cfm (0.94 m3/s) of air flows through a 10 x 12 inches rectangular duct.

Does duct length affect CFM?

Texas A&M did a study on the effect of flex duct not pulled tight and the results are astounding. In my article on this research, I showed from their results that a 6″ duct moving 110 cfm when pulled tight will move only about 70 cfm with 4% linear (longitudinal) compression and about 40 cfm or less at 15% compression.

What happens if return air vent is too small?

If the return duct is too small, there are an inadequate number of return grilles or they are undersized, it can’t return enough air to recirculate back into the system. The average duct system has 25% less return air than required according to National Comfort Institute.

What happens if duct is too big?

Your system pushes air into the ducts, but the ducts are too large for it to build up any sustained amount of air pressure, and thus a “forced air” system doesn’t have any force. As a result, you get poor air flow and no matter how hard your system seems to be working, you don’t get to feel the benefit.

What happens if ducts are too small?



Ducts that are undersized will increase the static pressure, which will result in excessive noise as air moves through the system. It is often loud enough to be distracting, so it will not be difficult to overlook and should be addressed, as undersized ducts overwork the heating unit.

How big should 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).

Is it better to undersize or oversize ductwork?

Fundamentals of Good Duct Design
An effective duct design also takes these factors into consideration: Proper sizing. All the ducts must be sized to match the HVAC equipment capacity. Using oversized ducts will erode the system’s efficiency, while undersized ducts won’t carry the necessary volume of air.