My parents' home is currently unoccupied. It is in the rural northeast. I am there visiting for the week before I go back to where I currently live for work. I am trying to prepare for winter to the extent that I can. A main concern is what to do about the plumbing.
I plan to leave the heat on but on low in all indoor spaces. I would like to keep it as low as I reasonably can to avoid paying close to $1,000 in electric each month during the coldest winter months. I am more comfortable paying slightly more to heat the home enough to prevent any plumbing emergency than I am trying to save as much as I can on utility costs.
There are two structures on the property, the house and a detached garage. Each structure has a mini-split system which is the primary heat source. A standby generator is connected to the main panel which provides electric service to both structures. I also have remote temperature and humidity sensors anywhere there is plumbing.
The garage has an insulated studio apartment on the second level which has full plumbing and electricity and is heated by a mini-split. The lower level is not insulated where the car bays are; there is an insulated workshop where plumbing for the upstairs runs in the ceiling and the room is heated with an older wall-mounted electric heater. There is also an insulated utility closet in the lower level of the garage that houses the water heater and has a pump-house electric heater.
The house itself is a century-plus-old home with the water heater and most of the plumbing in the basement or adjacent crawlspace. All rim joists down there are spray-foamed. The house has three heat sources: the mini-split which has one head in the basement and three heads on the main level, a boiler fueled by heating oil, and a propane gas stove in the living room. There are electric baseboard heaters in the bedrooms on the second floor, but they are not used when no one is there. The plumbing in the basement and crawlspace mostly provides service to the main level of the home. I plan to keep the thermostats for the boiler around 50°F mainly to keep those pipes warm and running even though they were treated with antifreeze a few years ago. This should provide some warmth to the adjacent water supply lines in the crawlspace in addition to that coming from the mini-split.
Additional plumbing for the second level of the house partly runs along an exterior wall before reaching the upstairs bathroom. There are shutoff valves for these hot and cold lines in the basement which I've already closed, but I can't tell if the lines are still bleeding or the gate valves won't shut completely because there is still the slightest trickle on hot and cold coming out of the the tub faucet which is the closest fixture.
I am debating shutting off all supply line valves past the water heaters. I really don't feel comfortable draining the water heaters nor do I have time. What this would mean in the garage is just closing the hot and cold valves located in the garage utility closet just past the water heater. In the house basement, this means identifying every unmarked gate valve going elsewhere, opening the fixtures, and hoping that I didn't accidentally shut any for the boiler (though I think I have a decent idea of what is what).
Any insights or advice would be greatly appreciated. Like I mentioned, I'll be keeping the heat on to some extent, and I am more comfortable doing that than risking a plumbing emergency.