I removed a piece of the drywall from inside a closet. The house is insulated well, fiberglass batts that reach stud to stud. However, if this matters or not, the "U" studs are not insulated. What I mean is the insulation is the same as a wood stud house, reaching from stud to stud and on these "U" channel studs, the insides are thus open - no insulation. However, on removing one piece of siding, the house does have a fibered type material underneath the siding, although I am not sure what R factor it would be. As for heating, the house is in Maryland, about 1 1-1/2 hr SE of Pittsburgh and it does get cold here. The heating system is 3 years old, forced air fuel oil, and yes it does do the normal sooty fuel oil thing. I am checking with Trane on a different furnace filter to use. The one in place is just a piece of fiber filter material which I replace monthly.