A greenhouse has one purpose: to provide and maintain the environment that will result in optimum crop production or maximum profit. This includes an environment for work efficiency as well as for crop growth. This publication is limited to equipment and methods used to control or maintain desirable temperature and other environmental conditions in a greenhouse during those periods when supplemental heat is required. Obviously there are many ways this can be accomplished from the standpoint of equipment used, types of fuel used, type of construction and management practices followed. Because each operation usually has some unique characteristics such as types of plants produced, level of quality of production strived for, type(s) of house (s) used and management procedures followed, it is important that all of these factors be considered when selecting and installing a heating system.