I guess the anti freeze would not be a necessity, but something to consider. My pipes run in the attic where temps go below freezing, so their is an aquastat to keep the pipes temp set at 50 with 120v line voltage going directly to the pump, if the fire would go out and the triple doesnt allow less than the low limit water to pump, things would freeze. Now my boiler in the basement would take along time to get to freezing (if ever) compared to an outbuilding. Have it set to keep the pumps circulating if temps in the outbuilding get to freezing. Just a thought. Ever go away for a couple days ?