We have run with the furnace on 45.
Disclaimer, many will urge you to turn the propane off at fuel ups.
Listen to all the pros and cons, then, make your call.
Before I started taking my violets, we ran in extremely cold weather with NO furnace on, but loaded with food and toiletries, etc. Only thing that seemed to really suffer (temporarily) was the olive oil, it like congealed, when it warmed up, it reconstituted itself. I could not tell in using if this hurt, I don't think it did, but, then, I am no gourmet cook, eh??
Now if you are considering running with water, that is another story, when we left the sticks on Jan 3d with 4 below actual temps, we went sans water (carry a couple of gallons of fresh water in old milk containers to flush with). One reason we did sans water, is that we were of no mind to pull a hose out of the pole barn, fill Tana's tanks and then try to get that hose thawed out for storage back in the pole barn. Call us lazy, but that just did not appeal at 4 below!
Enjoy your winter away!!