I have brought this up in past winters and I'll bring it up again. Sellers with a vacant house to sell need to recognize that cold snaps happen around here from time to time and trying to save on the heating bill by shutting down the furnace is a recipe for disaster. We are in a mild cold snap now with temps expected to dip into the teens in outlying areas and highs barely above freezing. It only takes 2-3 days in a row like that to freeze pipes in home that has the furnace turned off. Enter exhibit A, I showed a vacant mobile home yesterday that was 39º INSIDE the home. The thermostat was set to OFF rather than just lowered to say 58º or so. Keeping the house heated to 58º will literally cost $20-30 a month, but the nightmare scenario of broken pipes will cost thousands, and you might have to fight the insurance company if they find out YOU turned off the heat. I called the listing agent and told her about it; I asked permission to set the thermostat to 58º which I believe to be the minimum in our damp climate. 58º is widely accepted as ideal for keeping a vacant house from suffering damage. She agreed and disaster was averted. The listing agent did not realize the seller had turned the thermostat off entirely.
It would have only taken a couple more days for the pipes to freeze and burst causing thousands of dollars in damage. Had this cold snap been a real bad arctic style event that we occasionally get they would have already been burst by the time I arrived. We do get deep freezes here from time to time. If the seller is hell bent on turning off the furnace then they should have the home properly winterized by a professional. That will costs a few hundred dollars but will save a lot of money in the long run. Even modern well insulated homes will suffer heavy damage if left without heat for a long period as our damp cold weather will allow for moisture to form on surfaces allowing mold and mildew to thrive.
I have shown houses that had burst pipes when I showed up, one time back in December of 2009 I showed a very expensive mansion that had been repossessed by the bank and they had not winterized. Power had been shut off to the home. The extent of the damage was monumental. Heated travertine floors had been pushed up and broken by pipes breaking underneath and water was gushing through the ceilings from the upstairs, ice everywhere. The house easily had $200,000 in damage. That was a $2 million dollar home by today's prices, I think the bank had it listed at that time for $900k or so.
The rule is easy, 58º or winterize. Violate the rule at your own peril.