I'd like to tighten the thermal envelope and get the best bang for the buck and tackle the weakest links first. There is no underfloor insulation. Cinder block crawl space, handful of small vents. Vapor barrier on ground.
The outside has been done in vinyl with some sheet insulation under and then the old black fiber board under that, probably nothing in the wall. Need to look. Maybe R4 total. Windows are new and OK.
As poor as all that is, it isn't hard to heat. It's only 900 SF, natural gas heater. Flexible, I believe uninsulated or low insulated duct.
I'm thinking of leaving the walls alone for now, blowing in some cellulose later.
My first impression on the floor was to push in some fiberglass. Now, I wonder if I shouldn't insulate the crawlspace walls instead. Rigid foam board shiny side out, perhaps spaced off the wall to add an extra R1, perhaps not.