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Discussion Starter #1
I have an AprilAire 500 humidifier that is installed in a very tight utility space. The original installed did not place a bypass duct on the unit becuase of the confined limits of the tiny closet. I suspect that we do not get the full benefit of humidification without the bypass duct.

I have looked at the space I have there and determined that using an oval duct takeoff would fit between the two PVC intake and exhaust pipes. Then convert to 6" round semi-rigid flex duct, and proceed up to the AprilAire connector. I would need to modify the PCV Exhaust vent, removing a sweep elbow and replacing it with two 45 degree fittings to move the pipe away from the AprilAire intake connection.

My dilemma is cutting the oval hole needed for the takeoff fitting. I do not want to drop drill chips down inside the A-Coil just below the plenum where the hole must be made. I also cannot locate a 6 inch oval duct takeoff fitting with a "scoop" inside the plenum. I have seen discussions where the scooped fitting will direct more airflow into the attached duct connection.

Pictures are attached. Suggestions or ideas?
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You could use a hole saw as they cut metal and the cut piece stays inside the round cutter head. I would use one at the top of the hole and one at the bottom. Then buy some good quality offset snips ( not cheap ones as the jaws bend and then they are useless ) and finish the hole.

Or you could just do a bunch of 2" hole saw holes and yeah it may not be pretty but it will work. You don't need no scoop and it is just a small amount of pressure and flow needed anyway. The high pressure of the supply is more than enough to do the job. I also leave the bypass damper half way open on mine. You don't need a hurricane blast flowing thru it and too much can blow water off the evaporator wick inside the humidifier.

 

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I usually just use an angle grinder with metal cutter wheel. Makes a lot of noise, but it just drops a bunch of harmless dust. You do have to make sure there is nothing behind there for the grinder wheel to damage, because she'll go through a copper tube real fast!
 

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Discussion Starter #4
UPDATE:

I had our Heating & Cooling Service Company come out and install the ductwork yesterday. You can feel the "warmth" in the bypass duct going into the Aprilaire Humidifier.
Humidity level immediately started increasing in the entire building by about 1% every couple of hours. This morning, we are above 40%. (but it is warmer and rainy here, too...)
I always suspected that not having the bypass duct was limiting the amount of humidity we could get into the building. This verifies my hunch was correct.
The furnace closet was so small that it originally seemed impossible to find enough space, but with the correct arrangement of duct fittings, it worked.
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Looks good to me.

I hate using that plastic pipe for the bypass and the metal flex pipe is the cats azz. (y)
 
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