Seems is always a HOT (oooo, Carol, could not resist,
sorry) topic.
We prefer not to run with furnace on, but, have done so when we leave MI in 4 below and Tana is loaded with my violets. Run at lowest setting.
Best idea is to leave before the temps get that low, or lose the violets. Losing the violets is low on the list of possibilities.
Do what feels best and safe to you. Have a great time in your Monty.