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I would insulate the outside walls with the rigid foam board insulation like you described first, but do not do the floor at this point in time. Then see what kind of improvement that provides. I'm not sure what I would do about the existing vapor barrier that's on the walls. If you leave it in place and put the foam board on top of it, then it's possible ...


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In most cases, you would have both a supply and return in the crawl. If the crawl is properly air sealed/encapsulated, then the air in the crawl should be the "same" as what is circulated in the home, so no issue with a return in there. If it's not properly encapsulated, then I would take the steps necessary to do so before adding a return as you may ...


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