Family farmhouse, in Michigan, over 100 years old. We're debating on what temperature to set the thermostat at during the winter months. We currently do not have a programmable thermostat and everything I've read says 55 degrees is okay when sleeping and/or not at home. 68 degrees when home. Would this also apply to homes with 15ft ceilings and plaster walls? There are newer windows on the first floor. I am not sure about the outside and interior wall insulation. Please help!!