Skip to Content

Can You Use Flex Duct For Return Air: Let’s Find Out!

Flex ducts have recently become very popular. They’re a cheaper and easier alternative to conventional ductwork. Although they provide features similar to conventional duct materials, there are a few nudges here and there. 

So, you might ask: can you use flex duct for return air? 

Yes! You can use flex ducts for your return ducts. However, you have to make sure it fulfills all the necessary criteria. These include pressure checks, proper wrapping, and marking, airflow control, etc. 

In this article, we’re going to discuss everything you need to know about flex ducts. Let’s begin! 

Knowing How Flex Ducts Work 

Knowing how flex ducts work is key to deciding whether we can use them or not. Flex ductworks are generally made of lighter metal compared to the steel or aluminum of ductwork. Common materials include rubber, PVC, polyurethane, etc. 

To ensure malleability and strength, most ducts are given fiberglass insulation. As a result, the metal doesn’t break or leak, unless at tough angles. So there will be no hindrance for return air.

Return air needs to pass through the ducts and back into the system. Otherwise, the air conditioning itself won’t work properly. Flex duct is an affordable, easy-to-set-up way to help the return airflow back.

The lighter material ensures that the hot air passes through easily. The material prevents any overheating and prevents breakage. Since it can be bent to fit desired places, it’s ideal for running ductwork through floor trusses.

Using Flex Duct for Return Air: 3 Key Factors

Let’s ask ourselves the all-important question! Can you use your flex ducts for the return ducts in your air conditioning system? 

The short answer to this is yes! Flex ducts are a great addition to your air conditioning system. However, compared to conventional ductwork, it’s extremely technical. 

So, you need to ensure a few factors before getting into it-

Quality of Insulation 

The quality of insulation is very important for any ductwork system. To begin with, the insulation of the return duct is crucial. Any problems with the insulation will overheat the entire system due to the hot air.

Generally, we recommend that your ductwork should have the R12 insulation rating. However, most premade flex ducts are not available in R12, so you have to improvise. Your flex ducts need to be insulated and wrapped separately for better insulation. 

For this reason, use at least a plated filter or any sturdy material like Aluminium for insulation. Thus, knowing how to split flex ducts is crucial.

Pressure Control 

Pressure is another key factor in your ductwork. Too much pressure and your entire system might stop working. Again if the pressure is too low, the system won’t work. So, you need to control the pressure efficiently. 

When it comes to pressure control, the ratings on your air conditioning system are important. Most household air conditioning systems have a pressure rating of -0.25” to -0.5”. So, your ductwork needs to match this rating. 

We recommend that you remain on the safe side when it comes to choosing ducts. Suppose your system has a rating of -0.25. Then, make sure your ducts can withstand up to -0.5 This will prevent accidents in case the pressures surge up.

Make sure you have a clear idea about the pressure ratings of your duct. You have to set it up according to your pressure ratings. Otherwise, you can damage your system for the worst.


The biggest enemy for your return air is dust. If dust gets into the setting, it would slow down the entire system. Also, the dust could accumulate inside the machine and cause it to overheat. So, having a good filter in place is crucial for the duct as well as the system.

You can also add vents to your existing ductwork. This will be helpful if the system keeps overheating. In that case, make sure all the vents have proper filters.

If you’re wondering which duct to use, we got your cover. Check out our suggestions for the best filters for ducts here-

Product 1
Product 2

These are the best products out there in their price range. We hope you find them useful! 

Using Flex Duct for Return Air: 3 Easy Steps 

Setting up the flex duct for return air is fairly simple. Follow these steps and you’re good to go! 

Step 1: Measure and Cut Your Flex Duct 

The first step is to measure how much duct you need. Measure the distance between the columns where the duct will stay and the distance from your system. Make sure you’ve marked the ends and cut them off. 

Use a utility knife to cut the ducts, and then snap the wire with wire cutters. Take your time to measure and cut your flex duct carefully. Quite often people cut longer ducts for the sake of safety. However, this is actually riskier.

The friction in the ducts can damage the airflow as well as raise the temperature inside. So, make sure the measurement is accurate. The more extra duct you have laying around, the riskier it gets. 

Step 2: Add Mastic Glue 

On the end of your column, add a generous amount of mastic glue. Then, slip the duct’s inner core over the collar and into the glue. Make sure the duct is at least 1 inch deep into it and let it set.

Afterward, apply duct tape to cover the area and close any gaps remaining. 

Step 3: Connect the Ends 

Take the other end of the duct and stretch it up to the other end. Make sure there is no bunching up or sagging in the duct. Afterwards, similarly add mastic and connect it to the other end. Cut off any excess and you’re set! 

With that, we’ve discussed how to use the flex duct to its best! 


Question: Does return air need to be ducted? 

Answer: Absolutely! Otherwise, the return air won’t be able to circulate and go back to the system. Thus, increasing the temperature of the house drastically. 

Question: What happens if there is not enough return air?

Answer: If there is not enough return air, your system simply won’t work. The circulation will be disrupted and your system won’t keep up with the demands.

Question: What if I don’t have enough return air? 

Answer: If you don’t have enough return air, you need to improve the circulation of your house. Get your ducts cleaned and create a source for extra air. You can turn the fans on using outside air to help you out.

Final Word 

Ensuring proper circulation of your return air is important. If the air doesn’t transmit properly, it will only cause your system more harm than good. 

So, can you use flex duct for return air? Keep in mind that it depends on a lot of factors. 

In this article, we’ve discussed such factors to help you make your decision. We hope it helps you.