Hey HVAC pros and experienced DIYers — I could really use some guidance.

We have a 4-ton, 14 SEER Champion condenser (Model TC4B4821S) paired with an 80% AFUE gas furnace + cased coil, all located in the attic above our master bath.

Our home is 1833 sq ft (4 bed / 2 bath) in Rogers, Arkansas.

I have had extensive health problems since 2018 (whether coincidence or not, I’ll never know but that’s when we got our HVAC system installed).  I started suspecting a hidden mold issue when my diseases are well controlled by MAX meds, but I continue to be extremely tired all the time.  

Anyway…Recently we discovered extensive mold throughout the supply duct system, likely caused by a combination of:

• Poor ductwork design  

• Oversized equipment (system short-cycling, not dehumidifying)  

• Flex duct runs that were… honestly ridiculous  

We’ve already spent thousands on remediation/testing the home, (originally trying to find the source of mold, all the while it was hvac).  Recently replaced windows that were growing mold between panes, and we’re now at the point where we have to replace the supply duct system ourselves due to cost.  We will be paying to have the plenum replaced and installed, but not the ductwork because we simply cannot afford to. 

What I’m Looking For:

Help planning a proper supply duct layout (flex or hybrid metal/flex) that will:

• Improve air distribution  

• Reduce humidity/mold risk  

• Be reasonably efficient without going insanely over budget  

Current Setup (Supply is a mess)

The existing ductwork is all flex and poorly routed — crisscrossed, multiple exits off the supply plenum, basically impossible to defend & definitely shouldn’t be copied with new ducts.

Returns (Not Being Replaced)

Return system seems OK:

• Master return: 14x14 w/ 10” duct  

• Hall return: 20x30 w/ 16” duct  

Attic Info

• Blown-in cellulose, \~8–10”  

• New roof in 2022  

• Soffits now properly exposed (previously completely covered with blown in)

• 3 roof vents + 1 gable vent  

If anyone is willing to share best practices or even a basic starting layout for supply runs from an attic system, I’d be extremely grateful.

Thanks in advance — we’re trying to do this the right way after years of bad installation.

1st pic attached attempt to show layout/approx room sq ft and vents/return locations. The rest show prior vent runs throughout attic and closeups of the plenum connections.

DIY Duct Redesign Help Needed (Mold Issue + Oversized System)