The proper size of a greenhouse must be determined by a number of factors. It is never a safe policy to build a large house or an extensive range of houses without thorough experience in greenhouse work and full knowledge of local conditions and market facilities. A house 30 x 100 feet is probably as large as any market gardener should start with, and a smaller structure would be desirable where both capital and experience are limited. A width of 30 feet has been given, because this is the minimum width for economical construction, heating and operation; narrower houses do not provide as uniform atmospheric conditions, and the plants are more likely to be injured by direct cold drafts.