Choose the best electric greenhouse heater by selecting a unit with an appropriate heat output for the greenhouse size where it will be used, and that is equipped with a circulating fan and internal overheat protector. This type of unit serves to maintain a uniform temperature throughout a greenhouse, so that plants may be grown indoors without being exposed to the dangers of freezing. The continuous air circulation feature dissipates pockets of hot and cold air so that the inside temperature of the building remains the same for every growing table. They are safe for constant use, and are designed to shut off before reaching heat levels that can cause building fires.
The size of the greenhouse and local climate conditions tend to determine what size heating element is needed. An electric greenhouse heater can produce between 5,000 and 20,000 BTUs of heat to service small to large buildings respectively. Consumers may wish to use a heating calculator found online or at a local garden center, which factors in the size of the greenhouse, the outside and inside temperatures around the structure, and the insulating capacity of any lining materials, to determine how many BTUs are needed to adequately heat their building. A small greenhouse, for example, measuring under 6 feet (1.8 meters) along each wall, typically requires between 5,000 and 7,000 BTUs. This minimum requirement can vary for regions which experience extreme cold, and for plants that need very warm internal climates for growth.
An electric greenhouse heater with a fan that remains on constantly will distribute heat more effectively than one without this setting. Many heating elements are only equipped with fans that turn on while the unit is producing heat. Once the minimum temperature setting has been reached, the heat and fan stop running until the temperature begins to drop again. A fan that stays on after the appliance stops putting out heat will circulate the air in the building consistently. Heat is blown from warmer areas to cooler ones so that the temperature is uniform throughout and plants do not wither or freeze based on their proximity to the heater.
Heaters with an overheat protection feature prevent the appliance from becoming dangerously hot. An electric greenhouse heater generates a large amount of heat, and when the unit's motor gets too hot, it can short circuit the building's wiring and create electrical fires. Many greenhouse owners visit their structures a few times during the day, and are not present to constantly monitor the indoor heating element. A built-in overheat protection feature causes the device to turn off automatically when it is in danger of overloading the circuitry it is using, or when the heat output is approaching fire hazard levels. Owners can safely leave this type of unit on throughout the day without the fear of a fire hazard because of bad wiring or overly hot component housing.