Plants are comfortable at sixty degrees and protected from frost at forty degrees. Drops in temperature at night may prove a need for heat to be supplied. Heat is lost through glass walls, the floor, ventilation, and cracks or openings. This loss of heat can be detrimental to the growth of the plants.
A propane heater in the greenhouse is a low cost solution. The burning gas also provides carbon dioxide needed by plants to use the sunlight and convert it to energy. Make sure there is ventilation in the greenhouse and fans are strongly recommended to prevent carbon dioxide pools that are harmful to humans.
Some plants need extra heat so installing a heated bench or warming cables will save the cost of overheating the whole greenhouse. A propane heater is a low cost solution but should not be used in greenhouses made from polyethylene film as the plastic can melt or catch on fire.
