Even with a good furnace, freeze alarm dialer, etc. power outages
happen, furnaces break, and at cold temperatures a freeze can happen in
minutes. If you think about 5 gal per minute that is 3000 gal in 10 hrs,
7200 in 24 hrs. If it happens when everyone is asleep many thousands in
damage will be guarnteed. If I leave for a day in just 1 minute I shut
the main , open a house drain and all sinks. I have a good furnace but
everything breaks sometime. Bottom line it is not worth the risk of
leaving water under pressure entering your house, even in the summer if
it is vacant.