Abstract: Apparatus for automatic control of environmental conditions in building interiors, particularly in greenhouses where exacting conditions of temperature must be met. The apparatus consists of electronic circuitry for sensing and providing output indication of temperature, incident solar radiation, daily solar radiation accumulation and nocturnal temperature modification, an executive set-point and an insecticide control set-point, all of which outputs are applied to a summation device whereupon level detection actuates control circuitry to activate heating and/or cooling apparatus, insecticide control apparatus and other attendant equipment.