[ddsrph]

The photo shows the top (output end of my new Trane 1 1/2 ton heat pump air handler. As you can see the opening is bigger on the sides than the fan output duct by about 3 to. 4 inches. I am going to build a plenum to connect to my round ductwork the size of the full cabinet opening but was wondering should I have it cover the side openings or should they be left as part of the plenum space?

Thanks
JM

 

[Bitters]

Duct it to the top of the A/H.

 

[ddsrph]

Duct it to the top of the A/H.

Do you mean the full air handler top meaning it will be bigger than the opening?

Thanks
JM

 

[Bret86844]

The smoother the transition the less pressure is lost. If you can get a square to round transition piece to connect the outlet (narrower area) directly to the round duct, that would be best. However if you are just building a box at the end of the fan outlet and then your round duct is tapping off from a random side, it doesn't matter at all how you connect it.

 

[ddsrph]

Brett, Bitters
Thanks for the replies. The air handler is sitting on a framed in return air box
And I only have about 12 1/2 inches to work with between the top of air handler and a 90 degree 12 inch elbow pointing downward. The plan is to build a rectangular
Box to cover most of the top and then use two twelve inch flat to round taps held together by a six inch wide flexible connection. The two round taps which I will trim will take up about 6 1/4 inches of my 12 inch working space making the box about 6 inches tall. If advisable the two small spaces next to the fan duct will remain open and communicate with and be part of the plenum?

 

[beenthere]

Yep. Make the plenum to match the top opening of the air handler. Not just the fan opening.

 

[supers05]

Manual will specify. BT is right.

Cheers!

 

[Bret86844]

If advisable the two small spaces next to the fan duct will remain open and communicate with and be part of the plenum?

That is fine. Once you go with a plenum setup, you are basically just pressurizing the plenum and it can be whatever size you'd like. You only need to match the fan outlet if you are sending the air straight out the end into a duct.