slab | crawl | bsmt?
insulated at perimeter of slab | on outside of walls of crawl or bsmt?
were ducts sealed with mastic?
are elec boxes sealed to wall?
were penetrations into hse & attic sealed?
storm windows? [ they help protect expensive windows]
doors insulated & weatherstripped?
outside walls insulated?
hse wrapped against infiltration?
large gaps between framing & [window or door frames] ?
what are your DegreeDays?
compute kwh/DD/cu ft conditioned space --
[ just to know this usage -- U have other problems, now -- ]