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Connecting Duct Board Plenum to Air Handler [Explained]

It’s quite difficult to work with duct board plenums and an air handler. However, having an HVAC system in your home is pretty beneficial.

What should you do while connecting duct board plenum to air handler

Firstly, you’ve to get all the necessary tools. Then position both the air supply and return plenums to the air handler. Lastly, connect them to the air handler by using foil tape. And don’t forget to rub the tape down for a better result.

Now, this is just the basic info. To connect the two properly, you need some details. That’s why we’ve provided a step-by-step guide for you. 

Therefore, to install the HVAC system safely and smoothly, keep reading!

What Are Duct Board Plenum & Air Handler in HVAC?  

The duct board plenum and air handler are important parts of the HVAC system. What’s an HVAC system, you may ask? 

Well, HVAC is basically the short form of heating, ventilation, and air conditioning system. It ensures decent indoor air quality and thermal comfort. 

But to operate the system-

You’ve to connect the duct board plenums and the air handler properly. 

The air handler is the device that manages the indoor air throughout your home. 

Then you’ll find two duct board plenums for each HVAC system. One is called the supply air plenum and the other is the return air plenum. 

Furthermore, these two plenums need to be connected to the air handler. Otherwise, your HVAC system or air handler won’t function. 

How to Attach Duct Board Plenum to Air Handler? [3 Easy Steps]

Now, attaching duct board plenums to your air handler isn’t a piece of cake. You’ve to know all the essential steps to connect the two. You don’t want to make a mistake like using a flex duct for return air. So, pay attention-

Get All the Necessary Tools 

Well, to start your work, you need to grab the essential tools.

Tools and safety gear will keep you safe throughout the process. Because not following safety precautions can be dangerous.

Not wearing a respirator when cutting asbestos siding can cause lung diseases. 

So, let’s see the tools you’ll need:

  • Gloves 
  • Goggles 
  • Bricks or 2×4’s 
  • Aluminum foil tape 

Now, the foil tape is the main equipment for connecting your plenums to the air handler. Thus, you’ve to use good-quality aluminum foil tape. 

For your comfort, we’ve mentioned our favorite tapes for this job:

Product 1
Product 2

So, don’t just wait! Hurry up and get these tools. 

Position the Supply Plenum & Connect It to the Air Handler 

Now, once you’ve got the tools, you can get to work. 

So, first of all, you need to grab the supply air plenum. And position it to the hole that’s close to the blower access cover. Because that’s the spot where your supply air plenum should be connected.   

Then we suggest placing some bricks under your plenum. This way, you can prop up the very end of the plenum. And easily connect it to the air handler as it’ll be all leveled! 

Now, for the attaching part, you need to get the foil tape. Use 3-4 strips of it to seal the plenum into place. 

And that’s all for the supply air plenum! 

Position the Return Air Plenum & Attach It to Air Handler

After the supply air plenum is connected to the air handler-

You’ll be left with the return air plenum. Now, you’ll see another hole. And this one will be on the opposite side of the first hole you worked with. 

It’s located where the filter access of the air handler is. So, position the plenum to that hole. And use the same tools to level it. 

Once it’s all set, grab the tape again. And connect the plenum to the air handler. 

By the way, it’s better to press the tape strips down properly. Thus, we suggest using a hand applicator squeegee. 

Now to help you, my friend, here are our top picks regarding the squeegee:

Product 1
Product 2

Therefore, grab the squeegee to rub the tape down. And your plenums will be perfectly connected to the air handler! 

Important Tips on Connecting Plenum to the Air Handler

So, that’s almost everything you’ll need to know to connect the two. But it’s important to know some extra detail. 

Because these can be pretty effective while connecting the plenums to the air handler. Thus, here are some of the important tips regarding this issue:

  • When picking a glove, it’s better to use nitrile ones for this job. This type of glove is useful even while insulating ductwork in your garage.
  • While taping the plenum to the air handler, don’t hesitate to use more strips. Because this way the duct board plenums will hold the air handler tightly. 
  • Use a little bit of force while using the squeegee. Pushing down the tape with it will give you a great result.

So, these were some of the extra info that you should know! Therefore, keep these in mind while working! 

But if the work is too much for you, hire an expert to do it. This way your work will be done in no time. And to be honest-

It’s less expensive than putting new siding over asbestos siding

So, that’s all! Now, just decide whether you want to do it yourself or not!


Question: How do you seal a plenum?
Answer: Well, the answer is simple. To seal the plenum in place, use tape. However, you can’t just use any kind of tape. Aluminum foil tape is best suited for this. Also, make sure you avoid duct tape. Because its adhesive can be broken down due to the heat. 

Question: Can foil tape be used inside the duct?
Answer: Yes, you can. It won’t create any mess or problem. Because the heat won’t damage it. And the tape will also keep the connection intact. 

Question: Can I use Hardcast Mastic to attach duct board plenums to the air handler?
Answer: Well, it can be used. But it can get messy. Also, it gets super hard when it dries up. That’s why it’s better to use foil tape. 

Question: How long will the sealing last?
Answer: To be honest, we can’t tell you the exact time. However, we believe the sealing will last for at least 10-20 years. So yeah you can say it’ll last for long enough. 

Wrapping Up

Well, that’s everything on connecting the duct board plenum to air handler. Hopefully, you’ve understood how to attach them both. 

Were you able to connect the duct board plenum to your air handler

And good luck with improving the air quality in your home!