when it is abnormally cold like it is now I would say don't leave your house unheated as,apart from being cold it could cause problems that you wouldn't expect.
My ex husband was a heating engineer and years ago we had a cold spell rather like the one we are experiencing now.He was called out to a lot of places where their heating pipes had actually frozen overnight.He insisted we kept ours on constantly just turning the thermostat down overnight.I was sure our gas bill would be huge but it really didn't seem to have made a difference.
Dec