Air & Moisture Barrier with unconditioned Crawl Space
Unconditioned Crawl Space
Only Power Source Available is Electric.
Fiberglass Insulation between Floor Joists.
A/C Ducting with Insulation in Crawl Space striped tight against Floor Joists.
Create and air & Vapor Barrier between Crawl Space and underside of floor.
Reduce thermal bridge from Floor Joists.
And, most important reduce heating costs.
Based on above what is best method to achieve goals?
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The best approach is to convert your unconditioned crawl space into a conditioned crawl space. All the necessary details are in this article: Building an Unvented Crawl Space.
If for some reason you want to use the second-best approach, you can install a continuous layer of foil-faced polyiso insulation on the underside of the floor joists. The polyiso should be installed with attention to airtightness, with taped seams and canned spray foam or caulk at the polyiso crack at the perimeter of the crawl space. It sounds as if the location of your ducts will complicate any attempt to implement this approach.