Abstract: A heat exchanger with a tubular body having helical ribs about its periphery constituting expanded interior and exterior conductive heating surfaces. A clamp is captively held to the tubular body for mounting the heat exchanger to the exhaust duct of a freestanding heating unit. Hot gases passing through the exhaust duct conductively heat is the expanded surface of the tubular body and air therein. A thermostatically controlled blower directs the heated air within the tubular body towards a heated surface of the freestanding heating unit for convectively heating the area about the unit.

Abstract: An automatic air flow control system for a solar heating installation wherein thermostatically controlled dampers are associated with such solar heating elements as the collector and the storage area, and with the rooms to be heated, the thermostats being pre-settable to program their operations, with minimal supervision, in response to variable heat supply at the collector and variable heat demand in the rooms to be heated.

Abstract: A greenhouse is disclosed in which tubular curved members formed of standard unit lengths are used to form arched rafters while the same tubular members in uncurved form are used to form purlins. The tubular members are connected by suitable clamps to form a structural support for the roof of the greenhouse. A side leveling plate is provided on either side of the greenhouse to which the ends of the rafters are attached. The side leveling plate serves to anchor the rafters in the ground and also serves as a stapling surface for the covers placed over the roof of the structural support of the greenhouse. An environmental control system is provided in which the temperature, humidity and other environmental factors are controlled so as to provide enhanced growing climate for the tomato plants grown therein. Additionally, novel systems for correcting overwatering of the troughs as well as monitoring the water levels therein are provided.