Controlling Humidity in Tight Greenhouses
High relative humidity was very seldom a serious problem in lapped glass houses. During those periods of the year when outdoor temperatures were mild but too low to permit venting, the air moving through the cracks at the glass laps was enough to remove excess moisture. As outside temperatures fell, the temperature of the inside surface of the glass dropped to provide an excellent dehumidifying surface. These actions also removed heat from the greenhouse but heating was not a major production cost.
Source: • Connecticut Greenhouse Newsletter #108