I did the same thing two winters back with a $300 kit from one of those online stores. The best part was the report telling me my attic needed more insulation, which I could see with my own eyes from the ladder. What actually paid off was renting a thermal camera from Home Depot for $60, that thing found a bad seal around my basement door that was leaking cold air all winter. Fixing that cut my bill by about $30 a month.