Fabrication & Installation of HVAC duct work

[bigo46]

Hey,
I'm new at this but seeking advice from anyone proficient at this type of work. I have an existing home that I purchased a few years ago that I want to install HVAC ducting in. I purchased a TRANE 13 seer packaged unit for this house which has no central heating or cooling (Wood frame home built on concrete pillars in 1956) It has a simple gable style roof with a 4 on 12 pitch. It does have an accesible attic although room is limited. I will be running 11 registers off of the supply(Plenum) duct and I prefer to run the supply in the attic space. My question is how big should my supply duct(Plenum) in the attic be? My work space up there is limited so assembling a plenum in the space is not practical. It's possible to cut an access at either end of the gable and slide in a prefabricated plenum. What type of material is commonly used? The approximate size of the house is 1100 sq ft. It has single pane windows and no insulation in the attic. Insulation batts will be installed prior to constructing and installing plenum. Should I leave this project to a professional or can it be accomplished by myself?

 

[berkshire]

bigo46 (Marine/Ocean)
You have too many unknowns for a simple answer on this forum.
For example where are you going to place the furnace/ air handler.
I would suggest getting a professional involved.
B.E.

 

[MintJulep]

I have seen some awful hack jobs done by "professional" HVAC installers. Cutting collar ties, flex duct everywhere...

 

[berkshire]

MintJulep (Mechanical)
That brings to mind the old saw , That Noah's Ark was built by an amateur and the Titanic was built by professionals.

As far as the question about Plenum size is concerned there are knockdown plenums that can be assembled in the attic, but first you have to know the airflow requirements.
B.E.

 

[willard3]

You haven't even said where this building is; this will make a big difference in any answer.

 

[flyrfan]

You should hire a pro to do this work IMO.

There is more to installing a home HVAC system then banging sheetmetal together!

Who's doing the cooling & heating load calcs?
Who's sizing the ductwork to ensure you don't exceed your unit's ESP?
Who's going to properly install the refrigerant piping in accordance w/ industry practices? If you screw this up, you'll be throwing away lot's of money for someone to repace your compressor!
Who's going to charge the system? Federal Regs require you to be EPA certified to handle/purchase refrigerants.

This is not a DIY activity. Do yourself a favor and get competitive prices.