A greenhouse is a very useful space for the serious gardener because it allows year-round growing, regardless of the outside climate. In the coldest of temperatures, however, even a well-insulated greenhouse may need an auxiliary heat source to keep plants comfortable. There are several different kinds of greenhouse heaters available, including paraffin heaters, gas heaters, forced-air heaters, steam heaters, and electric heaters. Each type of heater performs best when space requirements and fuel availability are taken into consideration.
One relatively inexpensive heater is the paraffin heater. It works best in fairly small greenhouses or plant sheds and runs on a form of crude petroleum which is usually less pricey than other fuels. The crude petroleum necessary to run the paraffin heater may be difficult to find, however. The heater will not automatically shut off when the desired temperature is reached, and if frequent monitoring is not possible, one of the other types of greenhouse heaters may work better.
Gas heaters are very popular greenhouse heaters because the gas or propane used to fuel them is relatively easy to find. This type of heater also works best in smaller spaces because it does not have a fan mechanism to push air around a large space. Ventilation is very important with a gas heater, which gives off fumes and may damage plants. It is also important to find a gas heater with a tip-over shut off to reduce the risk of fire.
For heating large spaces, one of the most efficient types of greenhouse heaters is the forced-air heater. Usually fueled by gas, electricity or solar power, forced-air heaters use fans to blow air throughout the entire greenhouse. They require a duct system with access to outside air and can be connected to a thermostat to ensure an optimum temperature without constant monitoring. An added benefit of a forced-air heater is that the ductwork and fans can be used to ventilate the greenhouse in the heat of the summer, as well.
Steam heaters are popular with greenhouse owners who are concerned with fumes from other kinds of greenhouse heaters. Using either coal or natural gas, water is heated outside of the greenhouse and blown in through a ventilation system, keeping all fumes and smoke outside the building. The steam also sterilizes the planting soils which helps reduce disease and improve germination rates for seeds. While coal and natural gas are easily obtained at cost-effective prices, venting can be an additional cost consideration.
The final type of greenhouse heater is the electric heater. While these are the most expensive to install and run due to the constant need for electricity, this type of heater is excellent at providing a consistent, constant heat throughout a greenhouse of any size. There are also no fumes given off by electric greenhouse heaters. An electric heater can be set up either on the floor of a greenhouse, hung overhead, or plugged into heating elements situated within the soil.