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Old 05-06-2012, 02:20 PM   #1
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new ducts, air handler and compressor

I have a 2.5 ton air handler and compressor that will be charged before the summer. The air handler is residing in the attic outside the envelope. I'm going to suspend it from the roof joist so I can blow insulation under the air handler once everything is working properly.

I'm going to do the duct work myself and have an AC tech charge the system. All of my neighbors with similar town homes have a 2.5 ton system and say if works great.

I have 3 bedrooms and a full bathroom upstairs. I also have a dining room, living room, kitchen and half bath down stairs. I wasn't going to run a duct to the down stairs bathroom because it's very small(3 x 5 feet).

The questions I have are the following:

I need a return and supply plenum from the air handler in the attic. I've seen some plenum kits for about $60. Would you advise that I have a sheet metal shop make these and cut the holes or buy some sheet metal and cut the holes myself?

It looks like I will need 7 holes cut in the supply plenum to handle the 4 upstairs room and the 3 downstairs rooms. Is this correct?

Also to get to the first floor, I was going to run the duct work through the upstairs closets to the first floor ceilings. Should I install a connector that I can put in the second floor ceiling to connect the insulated duct work to and then run un-insulated duct work to the first floor since this duct work is in the envelope? Or, should I run insulated duct work all the way to the first floor ceiling?

If I do run insulated duct work to the first floor ceiling do I need a connector between the attic and the second floor or should I run a continuous insulated fex duct to the first floor?

Once I get the duct work done, I can braze the copper, run electrical to the compressor/AH and then have the tech charge the system.

Thanks for any advice?



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Old 05-06-2012, 02:27 PM   #2
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Do you know how much cfm each room requires? You're going to need to know that and then what size ducts to run to each room to deliver the required air.

Continuous duct would be best.

If you know that dimensions of the air handler's openings than most hvac supply houses will carry the pre-manufactured plenums for the unit.

They'll also have a duct hole cutter to make the holes, attaches to a drill. Don't forget manual air dampers so you can balance the air as needed, installed right at the plenum.



Last edited by Doc Holliday; 05-06-2012 at 02:30 PM.
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Old 05-06-2012, 03:31 PM   #3
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might want to install an emergency pan under the unit and pipe it with no trap out to the front of the house.just make sure your duct work is tight especially on that return so you get true space air and not attic air...
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Old 05-06-2012, 05:35 PM   #4
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I'm going to copy the exact same size ducts as my neighbors house which is very similar to mine. I think they have one 5 inch duct in each upstairs room but 7 inch duct work going to the first floor. I will check tomorrow.

So, I guess I will run 1 continuous insulated duct to the first floor without.

What should I use to seal the continuous flex duct going through the attic(2nd floor ceiling)? I don't want cool air going up into the attic.

I'm definitely putting a pan under the air handler and have a 2nd backup drain in case the AH drain gets clogged. I think this is code.
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