Novel approach to oversized A/C blower?

Old 10-10-19, 02:53 AM
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Novel approach to oversized A/C blower?

I have a 1600 sq. ft. loft with 15 ft. ceilings and an open layout. When our 3.5 ton Trane unit died on us about 2 years ago, we had an AC Guy install a new 5 ton Trane. He didn't change the ductwork or turn the blower down just installed the unit and left.

Needless to say, our ducts are too small for the pressure and the entire system is REALLY loud. Like so loud you can't talk on a phone even though the vents are 13 ft. above your head. It cools great but it's unbearably loud.

I have asked three different AC guys to come out and quote me on new ductwork figuring it couldn't be too difficult of a job since all the ductwork is easily accessible and exposed. Nobody has gotten back to me--they are all too busy and apparently ductwork is the least enjoyable part of the job.

Finally, I had a young guy come in and quickly assessed the problem and came up with a brilliant solution. Or at least it sounds brilliant to me.

At the main output duct, he's going to punch a 12" hole and connect a 12" piece of a flexible duct that will connect to a Honeywell, variable static pressure controller on the input side. Then the output from the controller will reconnect on the input for the system. Kind of like a loopback from output to controller to input.

This gives us a lot more air moving through our system, lowering the pressure through our main ducts. And this can be turned up or down depending on how cold we want it, how quiet, etc.

It will also ensure a source of air going to the input supply in case something were to cover the vent and no air could get into the unit. Plus the new air will already be conditioned so it will make the air colder.

He says this will extend the life of my 5 ton unit because it is having to do so much work to pull air through a tiny supply and push it out tiny ducts to vents.

Is this a viable solution? Anything I need to be careful of? Thanks in advance for your help.
Old 10-10-19, 09:16 AM
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I'd just turn the blower speed down and be done with it!
Old 10-10-19, 09:21 AM
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Good question on how that will work.
You can't just slow the fan down or the coil will freeze up.
Old 10-10-19, 12:20 PM
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That 12in flex duct will only move 390cfm at .08 static. Your duct will still be under sized a ton. Plus you are going to short cycle the unit so you are going to work the equipment harder not easier. You might have freezing issues as well. Has anyone done a heat load to see the exact size of unit you actually need?
Old 10-10-19, 06:51 PM
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What was the reasoning to begin with in changing the 3.5 to a 5 ton?
Even if the duct is fixed the unit will likely short cycle itself to death.

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