One Quick Fix For Low Airflow From Your AC Or Heating Vents

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If you’re reading this, congratulate yourself! You’re one of the tiny minority of property owners (homeowners) who are interested in the why, what, and how of keeping your home more comfortable, and improving Indoor Air Quality!

Hey, I get it. Go back and read our story on the “About” page, and you’ll quickly see that I was part of the huge majority of adults who never, ever thought about insulation and air ducts efficiency, unless it was to help someone in our church.

That all changed for me, when shortly after Easter in 1998 my father-in-law had this immortal conversation, “BIRD, how much insulation is in your attic?”

“Heck if I know, Charlie!”

“Son, you need to check it. If you can see the ceiling joists, you gotta add insulation.”

Abbey was 11, Beau was 7, and the three of us added cellulose insulation to our attic, and a 2nd attic two weeks later, (Another pastor wanted it done, because I had bragged about how much improvement it brought to our 1976 house).

And (unbeknownst to us) our family business was birthed in our hearts – and we didn’t even know it at the time!

What I’m trying to say is, there’s no shame in not knowing what we don’t know.

Now, let’s jump into our subject:

One trick for getting MORE airflow through our AC or Heating vents.

This only applies if you have flex ducts. Most of us have flex ducts, or a combination of sheetmetal and flex duct systems.

A flex (flexible) duct is a thin plastic liner with a coiled wire embedded in it. (Think of a slinky). Around the outside of the plastic duct is a fiberglass-insulated sleeve. Older flex ducts have about 1” insulation, and newer flex ducts may have up to 2”. There is a wrapper around the entire duct, which could be a shiny foil wrapper, or a grey or black colored poly wrapper.

The Problem With Strapping Air Ducts

Here’s the problem: installers use thin nylon straps to suspend and support the flexible ducts all over your attic, or under your floors.

These straps can easily create constriction points where they squeeze the ducts. Put two or three over-tightened straps on a single duct, and airflow can be really reduced!

When I see pinched and squeezed flex ducts, I add this service to our attic insulation upgrades. Our clients love the 2nd-mile service from me, because nobody ever takes the time to evaluate their air ducts!

And the huge majority of insulation companies only install insulation. No other services are provided. It’s sold like a commodity.

That’s the difference between being a SOLUTION-DRIVEN company, and a Product-Driven company.

It adds a few minutes to my site visit to check the ducts, and only adds about $50 – $100 on average – to their invoice – for me to fix those tight spots in their air ducts!

Here is my quick remedy for pinched and squeezed flex ducts that are resulting in low airflow:

Place a piece of metal flashing between the nylon strap and the flex duct. I call this piece of metal flashing, a “shim”.

The metal flashing (shim) will spread out the pressure, and prevent the strap from cutting into the flex duct, and constricting airflow.

Probably 3/4s of the time, I have to cut the original nylon strap and re-strap the duct with my own (improved) design, and include the shim.

This is especially important when a strap is used to create a “turn” or corner in a duct. I’ve seen these straps cutting into a duct so tightly that it was reducing airflow 30% or 40%!

Restrap the air ducts, using shims – and presto! You’ll be getting better, improved airflow from your vents!

You can see from the first photo, the duct is being pinched by the strapping, which doesn’t allow airflow to efficiently blow through the ducts. The photo below has one of Bob’s “shims” placed so the duct is no longer pinched and airflow is moving the way that it should!


Reduced Airflow in Flex Ducts is Common

Yesterday I joined our crew who was performing an Attic Bump-up Service, and installed 16 shims in our client’s air duct system!

Improving airflow in his air ducts was discussed in his virtual appointment. So it was already on our minds.

While in his attic for my site visit, I asked him & his wife to point to the rooms that were most uncomfortable.

They showed me the two bedrooms that were most difficult to heat and cool. With my eyes, I studied the air ducts that supplied AC and Heat to those rooms.

Using my laser pointing device, I showed them half a dozen constriction points in those ducts, and recommended that I restrap and shim those air ducts.

“Since this is your 2nd time to use our service, how about I “shim these air ducts” for FREE, to show my appreciation. Would that be a blessing for you, as my way of saying Thank You for calling us again?”

We all need to feel appreciated, and it brings me much joy to help our clients.

  • Using Applegate Bora Spray cellulose insulation, we improved their attic insulation to R-50.


  • We sealed and improved the insulation in their kneewalls. And blocked the joist bays in the floor system at the base of the kneewalls.


  • I re-strapped the air ducts and added shims, for improved airflow efficiency in their duct system.


  • We installed our Pull-Down Attic Stair Zippered COZY.

The entire job took Beau, Chris and me 3 hours. And that was from backing into the driveway, to pulling out after clean-up.

Have you got a room suffering with low airflow from your vents? Before you call the HVAC guy, use my “SHIM” trick instead, save your money – and be comfortable!

Thanks for reading!

Bob Bird

Bird Family Insulation


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