The One Duct Leak You Didn’t Expect

Sometimes, you just get lucky. Sometimes, you get sent out to install a unit in a closet! Although these types of installs have their challenges, at least for me, they have appeared easier on the surface. There is no return ductwork, as the unit sits on a platform. We are rarely disconnecting ducts in the attic to replace the plenum. So, aren’t we simply focusing on ripping out the old box and putting in the new one? Sounds like we might be home by lunch!

To some degree, yes. But there is one area that often gets overlooked when replacing closet/upflow systems: the dirty, damp, creepy area under the platform. Why do we need to deal with these spaces? Well, there are a couple of reasons. 

This quote from writer Wendell Berry has been pinned to the top of my phone notes list for the last few weeks:

“By the excellence of his work, the workman is a neighbor.”

It can be easy when we are fixing and replacing systems day in and out for a lot of our work to become rote. But let’s remember what it is we do each day. We are working on, upgrading, fixing, renovating, and generally trying to improve HVAC equipment and, by extension, people’s lives. 

You are being a good neighbor by caring for the homes you work in and taking those extra steps to make sure the work you do is thoughtful and durable. Now, not all of us get to choose how much influence we have over the scope of work, but as the ones on-site, we do have quite a bit of control. What can we do?

Return Grilles

One area where we can make big improvements to airflow for closet units is making sure the return grilles are properly sized. (Your customer will probably explode with joy with just how much quieter the system is from doing this.) 


Sometimes, the platform itself is made of thin plywood, has rotted out from water damage, or just looks terrible. Take the time to determine if it needs to be replaced. 

Air Sealing The Return

Credit: Building America Solutions Center

This picture is worth a thousand words. If your wall cavities under the platform are not blocked off with duct board, sheet metal, spray foam, or whatever material you choose to use, you’re going to draw some nasty stuff into that space under the platform.

Not only will you be drawing in dirt, but you actually have return duct leakage! On a system that has “no return duct!” Have you ever measured the temperature difference between the return grille and the blower cabinet on a closet upflow unit like this? Without some solid air sealing you will be adding load to the home as well as creating pressure imbalances between the living space and outside. This can lead to increased infiltration, comfort problems, and, gasp—that terrible word—organic growth.

So take some of that extra duct board you brought with you to the install and seal up those wall cavities. Set up that customer’s home for success for many years to come.

Matt Bruner



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