This is The Return Duct Size For 5 Ton AC Unit!

By - Ron Singh

Updated -

Determining the return size for a 5-ton unit is very important for accurate dimensions. Return air ducts channel the air from your room back to the air handlers.

The size of return you would need depends on the size of your duct, so what is the size of return you would need for a 5-ton unit?

Your 5-ton unit ac would need a return duct size of 22” diameter for a round duct and 19”×19” or 20”×22” if you want to install a rectangular duct. This size is suitable for the return duct for the 5-ton unit.

What Return Duct Size Does a 5-Ton Unit Need?

Return Duct Size For 5 Ton Unit

The size of the return air duct you would be getting for your 5-ton unit depends on if you would want a round or rectangular duct; the timely round return for your 5-ton unit is 2” in diameter, while for a rectangular duct, you would need a duct of 20” ×18” width by height.

Using the correct duct size for your device would save you from a lot of stress that comes with changing a duct in the future and several other issues. 

The proper installation of your air conditioning unit would go a long way in helping you enjoy your ac.

You should ensure that you have enough air vents to take out the hot air from home and enough vents to bring back warm air into the home; these vents are known as supply vents and return vents.

Improper sizing and installation of these return air vents can lead to an increase in your electricity bills. 

Follow these steps below to determine your air conditioner’s proper return duct size. 

#1. Step 1– Know the Tonnage of Your Air Conditioner

You can locate the tonnage of your air conditioner on the data tag, which you can find on the outside unit of your conditioner.

So, if you previously didn’t know the tonnage of your conditioning unit, you can get it on your data tag. 

#2. Step2– Determine the Shape of the Return You Would Be Using 

While some people prefer round return ducts, others prefer circular ones; so the next step is determining the shape of the return duct you would want to be using so it would be possible for you to get the correct size estimate. 

#3. Step 3– Calculate the Duct Size 

Now that you know the tonnage of your ac and the returned shape you would want to be using, you can calculate the return duct size based on these factors. The formula for calculating the return duct size for the rectangular duct is; 

Size of the air conditioner (let’s say 5 tons) multiplied by 144 sq/inches = return air duct you would be using in square inches; and for the round ducts, the diameter of the duct multiplied by 3.142= the return air duct in square inches. 

#4. Step 4– Determine the Grill Size 

The resulting answer is always squared when you multiply the size by the standard, which is either 144 or 3.142.

So, to determine your grill size, it would be the square root of your return duct size—for instance, 4 tons multiplied by 144= 576.

So, the grill size would be the square root of 576, which is 24. Therefore, the return duct and grill size would be 24 × 24. 

Next, you must convert the round duct area to square feet. In most cases, you would need these measurements to be square feet for your work to be more accessible.

So, if you want a round return duct, you can also convert these diameters to square feet by following these simple steps. 

  • Measure the diameter of the widest point on your round return duct. Let’s use 24 in this case. 
  • It would be best if you now got the radius by dividing the resulting diameter by two. 24/2= 12. 
  • After getting the radius, you should multiply it by itself to get the fair value of the radius; for instance, if your radius is 12, 12×12= 144. 
  • So, after getting the radius square, multiply it by 3.142, and now, you have the area of the round duct in square inches, that is, 144×3.142 =452.4 square inches. 
  • To get the value in square feet, divide the area by 144 to get the measurement in square feet. That is, 452.4/144 = 3.1 sq/ft. 

Following that procedure, you have successfully converted from diameter readings to square feet. 

How Much Return Air Do I Need Per Ton?

If you are unaware of the actual airflow, then you should work with 400 CFM as the airflow for each cooling flow.

So, if you are dealing with a 5-ton ac unit, the heat pump must be about 2500 CFM of airflow. With this table provided below, you can calculate the return air you need for your ac tonnage. 

Heat Pump in TonsMinimum Duct Size in Square Inches Minimum Return Size in Return Inches 
1 ½ 108300
2 ½ 180500
3 ½ 252700

When your control ACs do not have enough air vent for return airs, you notice that your room develops all sorts of problems ranging from cold spots to hot spots and premature failure of specific components of the ac.

Some factors influence the number of airs that return to the house; sometimes, the problem is not from the air vents.

Some of these factors include; 

  • The number of HVAC zones that you have in your homes. 
  • The size of your home and the dimensions. That is why I advise that you install the right size of ac and return the air duct to your home. 
  • The number of stories your home has. 
  • Get a lower return air duct for your air conditioner. 
  • Getting the wrong duct type and size for your house. 

What Happens When the Return Air Duct Is Undersized?

If the air going back into the house is too small, then the static energy in the house would be increased.

When this happens, you will face many issues, from the cooling, to the state of your air conditioner.

There are several ways you can remedy this issue, but the best method would be to remove the duct and install a new one the same size as the ac. 

Your HVAC system is responsible for cooling and heating the air circulated when it moves in and out of your house.

So, if you install a smaller size return air duct for your ac, the HVAC system won’t be able to work correctly. 

For instance, a 5-ton system would need a return air of 2000 CFM, but if you install the wrong return air duct, that amount of air would not be able to get into your home, leading to several hot and cold spots. 

Your duct size is essential in maintaining comfort in your home. And that is why you should install the right return air duct size. 

If you install the wrong return air duct size, your HVAC system is affected because the heating and cooling system would be affected.

When this happens, it may not be easy to cool out your AC sometimes, and if this persists, your ac can get spoiled in the long run. 

Apart from affecting the heating and cooling system, the discomfort you would be experiencing would be intense because a lower amount of cool air gets to the home.

Knowing that the return air duct in your home is undersized is very easy because the level of air getting into the house would be less. 

You can increase the air that returns into the house in several ways. These methods include; 

  • Modifying one or more of the return air vents in your home. 
  • Installing a new return air duct that can deliver the right size of your air to your homes. 

Remember, you are trying to get your system to deliver 400 CFM of air per ton and have to get into narrow paths like the hallways, so you would want to modify the amount of air that gets in a bit more to about 450CFM per ton. 

Can a Return Air Duct Be Too Big?

A return air duct can never be too big as there is no such thing as too much return. In extreme cases, a closed room is under negative temperatures, but that doesn’t mean your return is too big. Again, your home condition is the case here. 

What the return air duct does is that it filters out the debris and maintains air pressure, so the system maintains the exact amount of air it moves regardless of the number of air returned or how big they are. 

To determine your home duct size correctly, you should use a duct size calculator. For a 12×12 room,

First, determine the square footage of the room 12×12= 144 sq/ft, and when you use the duct size calculator, you will realize that the room would need 4×8 inches of air supply to match the average CFM rate given. 


Determining the return duct size for your ton unit, either 5,4 or even 3 ½, is very easy once you have got the hang of the calculations.

However, if you get confused at some point, call on a professional to help you calculate because once you have gotten the wrong value, changing it can be challenging and stressful.

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