Guess it's too late to ensure the lines are below the frost line??? Since the boiler is in a garage I would suggest antifreeze for the system. Your installer can recommend what to use. That way, if the system or elecrticity ever fail you'll be covered. Also, you can then run the Circulator on the thermostat. If your installer plumbed the bypass loop, boiler shock PROBABLY shouldn't be an issue. 100 pounds of coal or more a day during COLD weather would not be unusual. 30 minute run times to heat the boiler water back up not overly excessive since the water is constantly circulating.Are you using the boiler for domestic hot water? How much dead ash is on the grate under an extended full burn?