I have a new furnace for a seasonal cottage. The instruction book says that it should not be set lower that 60F/13C , as this might cause damage. I want to set it lower for when there is no one there-most of the winter. I left my old furnace (1970s) set at 10C and would like to do the same now.

What would the result be? Why is this required? I do not want to leave it this warm if possible.

Your thoughts? Thanks

Your new furnace could be a high efficiency furnace and as such will drain water as type of condensate. If you turn the unit down to low it could cause this condensate to freeze and damage the furnace.
Sixty degrees sounds a bit high but I would follow the book or call the factory to see why they printed that number. It could be a mistake.