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I have a couple active powered air filters hooked up on my ductwork. They are rated for 625 CFM at 0.5" W.C.

The ductwork is only used for AC, for heat there is a boiler and baseboard radiators.

They are in bypass. On the return duct line, there are duct takeoffs for the filters intake and output. If they are on they pull are from one part of the return line, and blow it into a further down part. If they are off, the air just goes by them in the return ducts.

When the air handler is on, it works properly because there is only one way for the air to go with with the air handler, and it's moving a lot of air. The filter pulls some of the air out of the return, filters it, and blows the clean air back into the return ducts. That's been verified with a laser particle counter.

The problem is when the AC air handler is off,it seems a fair amount of the filtered air is simply cycling inside the vents. There is still some air coming out the supply vents, but nowhere near what the filters are doing.

The instructions recommend at least 6' to 16' between the intake and output, but it's only just barely 6' and I think that's causing the issue.

I am looking at putting a simple 20x20 inch duct damper in between the intake and output, so that when the air handler is off, none of the air cane cycle between the intake and output from the filters, the output can only go out the supply vents.


So I am trying to figure out the best way.

I was thinking either a normally closed spring return 24v motor activated open wired with the thermostat wire. So when the 24 volt common and air handler close at the thermostat it will go to the air handler and the damper motor.

I wasn't sure if I should use a motor open and motor close, or motor open and spring close damper.

Is it bad for the motor to be energized so long with the spring return. That's why I was thinking a motor open/close with a timer relay that would open/close it based on the thermostat wire, and than turn itself off.

I also wasn't sure if I should wire it directly to the normal HVAC transformer or if I should use a relay and another transformer. I need to check the rating on the current transformer. It looks like the damper motor uses 6 watts 8v

https://blackhawksupply.com/products/ewc-controls-20x20-nd-rsd-nc-rectangular-damper-20x20-nd-motorized-damper-spring-return-normally-closed

https://www.hvacquick.com/products/residential/Air-Filters/Air-Purifiers/Amaircare-Airwash-Whisper-675-HEPA-Air-Purification-Unit

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