Hey guys, this is Luke from AirDuct Cleaning ATL. In the previous discussion, we talked about the spider duct system.
Now we’re going to discuss duct cleaning techniques for the trunk line system and how the process works step by step.
Spider System vs. Trunk Line System
So when designing an HVAC duct system, the two really only options you have are the spider system and the trunk line system.
The spider system is a more modern and flexible approach. Air supply starts at the plenum and then spiders off via the flex duct, which branches out like the legs of a spider and runs to the individual vents in each room. This is a more flexible option as the flex duct tube is not rigid and it’s easier to install and easier to move around any obstructions in the attic.
The other system is a trunk and run system, also known as trunk line. The trunk and run system starts in a main trunk that leads to several other branches or runs of that main trunk. Each branch is made out of duct board. The trunk and run can be more labor intensive and time-consuming. It can provide a better R-value (insulation value). However, the trunk and run systems have pretty much gone out of style in attics and homes nowadays because they have become much tighter, smaller spaces.
In summary, the spider system offers a more economic and flexible install for tighter attics, while the trunk and run system may in theory be more rigid or last longer. In this home that we’re working in right now, it has a trunk and run system. So, we’re going to show you how we approach cleaning that step by step.
Explanation
- Tools you’ll likely need for trunk-and-run cleaning: inspection mirror, flexible duct brush, HEPA vacuum, nuisance-filter media, personal protective equipment (gloves, mask).
- When to choose spider over trunk: tight attic space, lots of obstacles, faster/cheaper install required.
- When trunk-and-run might still be preferred: projects prioritizing insulation (higher R-value) and quieter, more rigid ducting.
- Safety note: always turn off HVAC power before accessing the plenum or ducts; consider professional help for major cleanouts
Our Trunk Line Cleaning Process
All right, so our process for cleaning a trunk line is pretty much the same as a spider duct cleaning.
Step 1: Floor Protection
We start with floor protection and plastic sheets. These are laid down to keep any dust or debris away from the owner’s furniture or any valuable items that they have.
Step 2: Vent Removal and Cleaning
After we do that, we remove all the vents (also known as cans).
This is what the can looks like without the vent.
We take those vents outside and clean them off with soap.
While someone is cleaning the vents with soap, another team member vacuums the inside of the cans — and in this case, the entire drop line — using the HEPA vacuum to get everything nice and clean.
Step 3: Negative Air Machine & Brush Cleaning
After we vacuum the cans and the trunk line, we hook up our negative air machine to the duct system.
We then feed in a 20–30 foot rotating brush head to stir up any remaining dust or debris that we couldn’t reach by hand with the vacuum.
Step 4: Encapsulation
Once the duct system is thoroughly vacuumed and brushed, it should be clean of any dust or debris.
We then go through and encapsulate it with our IQ8000 encapsulant, which helps seal and protect the interior of the ducts.
Step 5: Reassembly and Cleanup
After encapsulation, we seal up the duct system, reinstall the vents, and clean up the floors — and we’re done!
Accessing The Trunk: Cutting and Cleaning
What I’m doing right here is cutting into the trunk line. That way, we can access the downstairs duct system. We’re going to cut open holes throughout this whole trunk, vacuum, whip, and then encapsulate. So, this is what a trunk line system looks like. This runs probably about 8 ft down that way and then banks to the right and about 5 ft this way into the actual ahander. So, what we do to clean this trunk system is I’m going to cut holes into this trunk line about every 2 feet so we can get in there and get every every inch of it with our vacuums, our whip, and the encapsulate.
Negative Air Setup and Sectioning
All right, now we got everything vacuumed out, the cans in the trunk. So, our next step is to hook up negative air and then whip out all the trunk line. This system is a little difficult because we have a upstairs and a downstairs feed from the trunk line. So, what we’re going to do is kind of break it in two. We’re going to block off right here. We’re going to block off the upstairs from the downstairs so we have better suction from our negative air machine and we can get more of that dust and debris out of the duct system. So, we’re just going to put a piece of duct board or a cardboard plug right here so that our negative air machine is only pulling air from half the duct system and not the entire trunk line. Yeah. So, this is our negative air machine. This is what gives us the negative air pressure and sucks that dust and debris out of the duct system.
Encapsulation With IQ8000
All right. So, our next step is encapsulation. We use this paint sprayer here. Put it in a bucket of IQ8000. This is our Schmice encapsulent for duct systems. What we do is we go into the plenums and the cans and we spray on with this paint sprayer a thick layer of this white encapsul. And what that does is it both soaks into the duck board and creates a new lining for the duck board and it also is a antimicrobial encapsulate so it kills any leftover microbial growth.
Resealing and Wrap-Up
All right. So, after we encapsulate the trunk line, this is a section of our trunk line here. What we do is we have to reseal the holes. So, see, we have to reseal these holes. What we do is we use spray glue around the perimeter and then tape over it with foil tape and then brush over it with a water-based mastic seal. And then at that point, our ducks are sealed.All right. Now I put in the caps sling. All we have to do is put a vents and clean up. The house is smelling nice and fresh. So this is a duck clean with the trunks of it. Green box out
How often should I have my air ducts cleaned for both spider and trunk line systems?
We generally recommend an inspection every 1 to 2 years and a full cleaning every 3 to 5 years, depending on dust load, pets, recent renovations, smoking, and allergies. Trunk line systems with older duct board can hold onto dust and fibers a bit more, so if you notice buildup at vents, musty odors, or visible debris in cans, it’s a good sign to schedule sooner.
What is a negative air machine and why do you section off upstairs and downstairs?
A negative air machine creates powerful suction so debris dislodged by our brush and whip tools is pulled out safely instead of drifting into your home. When a trunk serves multiple floors, we temporarily block one side so the machine focuses on a smaller section. That stronger pull captures more dust and reduces the chance of re-depositing fines deeper in the run.
Is cutting access holes into the trunk line safe for my system?
Yes, this is standard best practice for thorough cleaning on trunk-and-branch layouts. We make small, strategically placed openings, clean each section comprehensively, and then reseal with spray adhesive, foil tape, and water-based mastic. Once cured, those patches are airtight, durable, and often tighter than some original seams.
What does the IQ8000 encapsulant actually do inside the ducts?
After vacuuming and agitation, we apply IQ8000 as a white coating that soaks into duct board and creates a fresh inner lining. It helps lock down any remaining microparticles and includes antimicrobial properties to inhibit leftover microbial growth on the surface. Used correctly, it improves the surface integrity of older duct board without restricting airflow.
Will encapsulation reduce airflow or leave a smell?
Applied properly at the manufacturer’s coverage rate, encapsulation does not narrow the duct or affect static pressure in any meaningful way. There may be a mild “new coating” scent during application and curing that dissipates quickly with ventilation. When we’re done and the system is back on, most homeowners notice a neutral or fresher smell.
How long does a full trunk line cleaning take?
Most single-system homes take about three to six hours, depending on access, number of branches, and how much sectioning we need to do. Homes with upstairs and downstairs trunks, tight attic spaces, or heavy debris loads can run longer because we’d rather be thorough than rush.
Can I DIY trunk line cleaning?
Without proper negative air, controlled agitation tools, and the right resealing materials, it’s easy to release dust into the home, damage duct board, or leave leaky patches. We’re happy to show you exactly what we do, but for trunk-and-run systems, professional equipment and technique make a big difference in results and cleanliness.
