When I sold my sticks n bricks home, the new owners replaced the "thermal drapes" with mini-blinds and wondered why their heating bill was so high.
I had given them copies of my gas bills for the previous five years so they could see what to expect for heating costs. In the first winter; their gas usage was 50% higher than my five year average. Factored in was "heating degree days".
They also cut down two 40 year old silver maples which kept the house in the shade most of the day in summer. Yup that combined with removing the drapes resulted in electric power usage that was double mine.