we have a 2300 sqft 80+ yr old house that has little insulation and single pane wooden windows. Last year we would set the temp on our t-stat over night to <40 deg to stop the furnace from turning on. Winter gas usage was over 175 therms a month last year so I am wondering if it's actually less efficient to let the indoor temp drop to 50 at night and then bring it back up to 63 in the morning, than to say keep the temp at 60 overnight.
our furnace is 90+ efficiant natural gas forced air 95,000 btu i believe. It's slow, raises the temp about 4 - 5 deg per hour.
What we were told way back when,is that you save one percent(of the gas that you would be usingt) for every degree that you set back over a 10 hour span.It is not a lot of gas per day,but it should be enough to see a differance at the end of a month.