Where to locate HVAC ducts in vented crawlspace – GreenBuildingAdvisor

I’m in climate 4c (Pacific northwest) and looking to put HVAC ducts in a vented crawlspace of a future build.  Vented crawlspaces do well here in the PNW and I prefer to not condition it. Attic is also vented.

My contractor gave me two options:

1. Run insulated HVAC ducts in an open web floor truss system

2. Run insulated HVAC ducts in a chase running under the floor system

Will these options be a recipe for moisture issues?  I’m worried that if/when HVAC ducts leak, I’ll have a wintertime situation where warm air will hit the cold floor truss framing, condense, and lead to moisture issues.

There is also option #3 – condition the crawlspace, and run ducts in the open web floor trusses, but that comes with its own challenges (radon mitigation, dehumidification, etc).

Janelle