An 11 by 15 meter free span, gutter connected, double polyethylene clad greenhouse was equipped with a porous concrete warm floor heating system. The warm floor heating system consisted of a 30 cm deep, vinyl swimming pool liner, filled with 20 cm of bluestone and capped with a 10 cm layer of porous concrete. It was filled with water to a depth of 20 cm and heated by a hot water boiler through a network of 1. 3 cm diameter pipes embedded within the bluestone. Supplemental heating was supplied by a water to air heat exchanger connected to the boiler. Cooling was achieved by forced air ventilation. There were three stages of ventilation with a maximum capacity of one air change per minute. This paper discusses tests conducted in the greenhouse, along with instrumentation hardware, the software program, and system operation.