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Old 04-11-2021, 03:47 PM   #1
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Join Date: Dec 2020
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M.O.C. #27665
Improved A/C Intake Ductwork

I have been disappointed with my living room A/C system ever since I purchased my 2013 3625RE Montana. I have considered replacing the unit with something more powerful, but could not find anything. On hot days, the unit never did well. I even set the bedroom unit, which seems to work better and shares the distribution ductwork with the living room unit, to the low 60s so that it could assist the living room unit. Alas, I learned to accept the shortcomings of my A/C.

At one point, I attempted to improve airflow by cutting off two of the vanes from each of my living room rotating ceiling vents (photo 1), so there would not be as much backflow pressure. That seemed to help a little bit, allowing more air to flow through the living room vents. But it was no panacea.
A few months ago, while watching a YouTube tour of the Montana production line, the host made a comment that interested me. He was talking about how Keystone has done a lot of studying and configuring of the ventilation system over the past few years, and suggested that adding a return duct to the system, 36 inches up from the edge, would significantly improve the performance. That started me thinking: Maybe it wasn't the outflow of air that was the issue, it was the inflow of air into the unit that needed work. So, I decided to take on a small improvement project.

First, I purchased two new return vents of the same size as the originals, and used them to trace an outline of where I wanted to cut my ceiling. I wanted to cut out only the square areas above the actual grill vanes, and leave a perimeter and center member so that the ceiling could help prevent my filters from being sucked into the duct. Then I took my oscillating cutter and cut open the ceiling, exposing the ductwork. A boxcutter was used to cut the soft "duct" material gain access to the inside of the duct as shown in photo 1. Repeat for the second square hole.

The first thing I noticed when I cut open the ductwork was that the duct had collapsed, resulting in a significant reduction in allowable airflow. You can see in photo 2 how much of a sliver remained. No wonder my A/C was not working well…it couldn't breathe! To solve that problem, I cut foot-long lengths of thin 1.5" OD schedule 40 PVC pipe, which I used to prop open the ductwork. The pipe runs from the original duct to the new duct to minimize the amount of collapse between the two. Another pipe runs between the new duct and the A/C unit, preventing the duct from collapsing as shown in photo 3.

Using foil tape, I taped the ductwork to the ceiling to maximize the opening, and taped the PVC in place between the ducts as also shown in photo 3. I then used the grillwork as a stencil and cut a new filter from semi-rigid active carbon-based filter material to match. The filter is held in place by the ceiling and the grill screws so that it will not be sucked into the duct.
Repeat on the other side of the ceiling unit.

The end results are dramatic. There is so much more air flowing through my living room system, that we actually adjusted our temperature settings by a degree or two. The system is a little bit noisier, with the new ducts much closer to the fan unit. If noise is a concern for you, I might just double the existing openings, keeping them close to the edge and further away from the A/C unit. For me, the better cooling more than outweighs the additional noise.
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Old 04-11-2021, 03:51 PM   #2
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M.O.C. #20472
I’ve done in the return air ducting but never thought about this in the supply duct.

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air conditioner, intake, return

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