1100sqft cottage, 3 bedroom 1 bath open concept kitchen, dining and living room and 10x8 mud/laundry room addition. 40 inch crawl space on piers, sand ground with 8 mil polly covering it, outer walls in crawl space skirted with wood and 2 inch Styrofoam, under floor is pink fiber held up with stapled strapped Tyvek. Cottage and garage are both 70's 2x4 stick frame, new insulation and vapor barrier when we bought and did a full gut reno on the cottage, also pulled the oil furnace and went to propane, pellet stoves in both cottage and insulated unattached 24x26 garage. We leave the furnace at 58 when were not there, no ducting underneath never had any pipes freeze. Turn the furnace up to 70 and pellet stoves on when we get there, up to temp within the hour and the furnace doesn't run again till about 12-24 hours after we leave (we usually leave the pellet stoves running after we leave till they run out of pellets).
We hang out in the garage living/party room 90% of the time, ceiling fan and window wide open with a fan in it on high blowing heat out, as even on lowest burn setting it's tough to keep it at 70 or under. Once that slab floor in the garage heats up it holds the heat well, usually only 4 days home before heading back up and it stays above freezing in there, usually around 10 deg, I think the coldest I've seen it was 5 deg.
Two 420 tank fills a year and a bag of pellets every 24 - 30 hours for each stove ($6.50 a bag) while were up. Cost for both propane and pellets is $1200 to $1500 a year. Small price to pay for the convenience of leaving it heated and not messing with draining plumbing. Growing up with a family cottage my dad would always shutter the place every week, usually always had to screw with getting the water going, 3 - 4 hours till you could get down to a sweater, furniture and bedding held the damp cold till well into Sat eve LOL
Never bothered to see what our cost would be shuttering every week and re heating from what ever temp it dropped too, I bet it wouldn't be a very big difference. Defiantly not worth the inconveniences to us anyways.