Yes, and I recommend it in sub-freezing weather. It will keep your water pipes from freezing, within limits. I've done it and was successful in weather in the teens, but would not rely on it for much lower temps.
"Those who expect to reap the blessings of freedom, like men, must undergo the fatigue of supporting it." Thomas Paine
'08 34' Classic SO, '12 Ram 2500 4X4, 6.7L Cummins.