A helpful explainer
I've been researching this and have landed on just leaving it on a reasonable temperature. We used a geo-fenced smart thermostat with our boiler in a cold climate and were 100% for turning the heat down in most circumstances. Now we are in hot humid NC with a heat pump, a dog, no insulation, and a spouse that works from home. Outside is never more than 30 degrees from our set temp (77 cool, 62 heat) and we need dehumidifying in the summer. I've not installed a smart thermostat yet (need to run a C wire), but given the circumstances and slow temp changes and my research, I'm not inclined to set the temp up/down further, except when on long trips. (My lovely neighbor takes care of our dog for free while we are away, but she sets the temp down to 66 (for the dog?) and doubles our electric bill, but I can't question her about it!) I am looking at attic insulation once I've done some electrical work and an attic exhaust fan plus some air sealing, but am not seeing a huge need as our electricity is <$150/month and no gas, which makes solar less compelling (also not expecting to be here terribly long).
The BTU savings doesn't include the amount required to rewarm the house so the savings is a bit less. Any chance you can do a spreadsheet showing the kilowatt hours or cubic feet of natural gas required to rewarm the house?