PROBLEM TO BE SOLVED: To provide an inexpensive greenhouse heating system highly reliable, causing no total decay of farm products even if put to failure, also having ventilative and sprinkling functions, usable semipermanently, and usable for cooling in summer as well.SOLUTION: A greenhouse heating system is provided such that a plurality of heat pump water heaters for domestic use are connected to a subtank with a predetermined volume, hot water in the subtank is fed by a pump into piping equipped in a greenhouse and circulated, the temperature of return water from the greenhouse is sensed and used as an alternative to the temperature in the greenhouse, and based on the temperature, a control of varying the operational number of the water heaters is made.【課題】低コストで、信頼性が高く、故障しても農作物が全滅になる事が無く、送風や散水機能も備え、半永久的に使用可能で、夏場の冷房にも使用可能な、温室用の暖房装置が求められている。【解決手段】所定の容積を有するサブタンクに、複数の家庭用ヒートポンプ式給湯器を接続し、サブタンク内の温水をポンプで温室内に施設した配管に給湯し、循環させる。温室からの戻り水の水温を検知して温室内の気温の代用とし、給湯器の運転台数を増減する制御を行う。【選択図】図２
