House: built in 1912, central Ohio. 2 story, 2000 sq ft. w/ newer insulated windows but minimal to no insulation in walls.
Furnace: 90+ nat. gas forced air, 3 years old, correctly sized.
Our "comfortable" temp is 69 degrees. How much should this be lowered during day (at work) or night (asleep)? How much would be too much?