Anyone who has spent even a moment in a greenhouse on a bright, sunny day can attest to its ability to magnify the sun’s energy. The abil­ity to admit light and use the energy for warmth and plant growth is one side of the story. The other side is the inability of the greenhouse to retain any significant portion of that heat energy after the sun sets. Any attempt to insulate the greenhouse in a conventional manner would severely reduce the admission of light that is critical to good plant growth. Therefore, the need for supplemental heating is apparent.

With rising energy costs confronting every greenhouse professional, the choice of heating systems deserves some thought where the oppor­tunity for a choice exists. Nearly all systems are automated now, and many involve both primary and back-up (emergency) systems.

Depending on the size of the greenhouse and to some extent the length and severity of the cold weather season, the heating system may be either a localized system or a central system. Localized heating sys­tems are contained solely within the single greenhouse or section of a greenhouse that they are intended to heat. A central system is more like the heating system in a large building. It has a boiler that produces heat to warm a number of separate greenhouses throughout the range.