There are other threads on this, I know. I've looked through then. I'd like to keep this concentrated on a particular topic which I think is worth revisiting, and probably relevant to most people.
My house temperature cycles as follows: thermostat to 55 F when away at work, and then spike up to 66 F for when active in the house, and for 62 F at bed time. I want to optimize.
From an efficiency standpoint, I would think the temperature should be as low as possible when unoccupied, as long as it's not so cold that the pipes freeze and our cat is significantly uncomfortable. From what I've read, cats/pets have fur and so are totally fine within any typical human indoor temperatures. Pipes freezing is variable and depends on the location in your house and insultion/etc. My pipes are mostly exposed and insulation in reasonably good... no pipes are located inside exterior walls; I do have pipes in a underhouse crawlspace, and I monitor the temperature. So, I'm not so concerned about pipes freezing.
What I am thinking about is the effect of more extremely temperature cycling on the house and whether this will cause bad things. For example, constant expanding/contracting of the building materials, and cycling humidity levels.
Along this lines, any thoughts/experience on the lowest practical away-from-house temperatures?