I had to fire up my LP heater. The two electric heaters couldn't keep the temperature above 45 F in the exposed greenhouse. The lean-to (orchids only) greenhouse is holding at 55 F. It may be a long night. It is ONLY 27 F here with a wind-chill of 16 F, but is supposed to get down to 13 with a wind-chill of 7. The wind is really blowing.