How important is insulation on ducting underhouse on heating/air systems, customer said older unit worked better, but new system not as noticeable, also house @ 2,000 sq ft, unit is a train-modelxv90, sound right f home size? thanks mike s.

If the ducts are run under the house itself in a crawl space, insulation is a must! When the heat isn't running, those ducts fill up with cooler air so when the heat comes on, it pushes that cool air into the house first. And there is terrific heat loss in the duct work if in a crawl space.