Every night my automatic thermostat reduces my home temperature from 68 to 55 degrees. I like cooler sleeping and wondered if I could turn it down even lower. But is there a point where the savings earned by reducing the temp will be offset by the time it takes to warm the home in the morning? Can I go too low? I have a forced air furnace with natural gas fuel. The furnace is 3 years old but is not a super efficient model. It still has a metal flue to the outside.