[DavidDeBord]

See if this helps

:cheers:

 

[DavidDeBord]

They have flex going from the package unit to the supply and return and it isn't in the best of shape either

There's part of Your Problem.

Any duct coming from a Package Unit,for Mobile Home/ Modular applications absolutely needs to protected from the Weather, & have minimum restriction for air-flow.

 

[DavidDeBord]

It's a doublewide and they currently only had one return and it was a 12 by 20. I was planning on increasing that one

"12 by 20" Floor Grill, or 12 x 20 Duct?

If it's a floor grill, what size duct is connected to it?

 

[DavidDeBord]

Also the doublewide doesn't have the vapor barrier underneath and most of the insulation is gone that's why I waa leaning toward a 3 ton and i was going to replace the flex with round pipe

Your Load Calculations have to be for what is "Existing", which has to include the floor insulation falling down. The original unit "may" have been correct for when the insulation was intact, but, now it is inadequate.

Installing Metal piping is an excellent improvement but, it should at the least be 26G, with External, Weather resistant insulation. All in all, Your local Building Department, can tell you want they want to see at the job-site.

 

[DavidDeBord]

That 12" x 18" can be converted to Round Pipe, but in most cases, it's going to be far larger than 10", or 12" Round pipe.

And I Agree Kdean, ... If an Installer intentionally reduced the Duct Size specified by the Manufacturer , just to save a $, or did it out of a Lack of Knowledge, ... then Many Problems are soon going to occur.