DIYer Duct Work Advice/Direction


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Old 04-17-19, 06:14 PM
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DIYer Duct Work Advice/Direction

Hello all,

I am a DIY homeowner (for most things). I had an AC system installed a year ago, long story short the people put in a 3ton, it didn't cool the house properly, so they went straight to a 4 ton. (Don't ask) The 4 ton is too big for my home (1650 sq feet, 10 ducts). Even more so is the main trunk line is extremely too small for the unit. (11x14 external, and drops even smaller towards back of the house). After having two people not wanting to do the job, I figured I would do it my self.... and I know it will be done right. The job is fairly straight forward - the trunk line is about 45 feet straight and sits on wooden stands. I can almost stand up for the entire job, and I have access near both ends of the trunk line. Correct me if I am wrong, but I should be able to just lay out the new trunk line and then make my connections.

Anyways, I am looking for some help to what parts will be needed and to make sure I size it right. I have been told to go with a minimum of a 16" trunk, but I thinking to go with 18". I will list my home details below to help determine this. While getting a feel for the job, I recognized the old duct work to the trunks is very lightly insulated so I might as well replace that. Taking the vents off and measuring say a 7" hole, I would assume I then need 7" duct work, correct? BTW everything will be R8 insulated.

Most importantly, I am not sure what I need to connect the trunk line to the air handler. I am hoping someone can point me in the right direction of that. My air handler is a York AE60DX21. Also what part do they make for the end of the trunk line that I will need to close it off?

On a side note, will 100 yards of foil, a gallon of mastic, and 150 yards of fiberglass tape be sufficient for this job?

Thank you in advance for any and all help provided!

Trunk Line 11H x 14W
Bedroom 1 7" Duct
Bedroom 2 7" Duct
Bedroom 3 7" Duct
Bathroom 1 5" Duct
Bathroom 2 5" Duct
Living Room 1 7" Duct
Living Room 2 7" Duct
Dining Room 1 7" Duct
Kithchen 1 10" Duct
Laundry Room 1 7"
 
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Old 04-18-19, 02:58 AM
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It would help to know where in the world you are since the climate makes a big difference in the size of the A/C unit. By my rough calculations, the 3 ton may have been too large especially where I live and the construction of the house. How did you know that the A/C unit was too small? Was it working properly? Being a good "tin knocker" is more than just buying some ducting and putting it in Where are you getting the needed duct size from? 11X14 is an odd size for trunk line. Is the duct insulated on the inside? Please add much more information. The younger A/C boys will be along to help.
 
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Old 04-18-19, 04:10 AM
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I am in the Tampa Bay Area. House faces west/east with no shade, so gets blasted with heat all day. Fresh insulation blown about 18 months ago. I had a three ton, went bad right before Irma hit so had a company put in a new three ton. I think they did it wrong and just slapped a 4 ton in (didnít charge me anything more) 🤦*♂️. Original trunk line 11x14 with insulation. Ducts off trunk line to vents look to be metal with very little insulation. Just looking at Home Depot to get all the duct work and supplies.
 
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Old 04-18-19, 04:53 AM
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That AHU sounds like a 5ton. So you have to deal with 2000 cfm of air. IMO you need to do a heat-load to see exactly what size unit you need. I feel you are going to have major humidity issues if this unit is over sized like it sounds like it is.
 
 

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