I'm not suggesting adding anything. Homes have lots of stuff in them. Everything in your house becomes a thermal battery - tables, chairs, beds, walls, counter

I'm not suggesting adding anything. Homes have lots of stuff in them. Everything in your house becomes a thermal battery - tables, chairs, beds, walls, counters, clothes and so on. Just allow a range of temperatures and when energy is very low cost drive the indoor temperature to the upper range. Ideally you have a brick/stone home with good exterior insulation.