An alternate Greenhouse Auto Vent system runs on the fog or good mist injected into the intake air stream. Although a number of commercial systems can be found, growers can assemble and install their own system utilizing a high pressure piston pump and fog nozzles. The basic components are shown in Fig. 1. A two-stage system controlled by a two- stage thermostat allows more water to be applied on excessively warm, bright days. Temperature settings ought to be 5-10°F apart.
Algae development in the pads may become a problem that may decrease the effectiveness of the machine and result in accelerated deterioration of the pads. The addition of an algaecide to the water supply will help in control.
It really is desirable, especially in hard drinking water areas, to add a wetting agent to the drinking water to obtain more 
uniform wetting of the pads. A commercial material or liquid home detergent at the rate of 2 tablespoons per 100 gallons may be used.
Drinking water for the pads should be clean and low in mineral content to prevent clogging and coating of the pads. A pump, pipes and gutters are used to recirculate the drinking water. A flow rate 113 gallon per minute per linear foot of pad program should be provided to make certain adequate wetting.
In the most common coolant system (fan and pad), the fans draw air through wet pads that extend the length of one endwall or sidewall. Aspen and coated cellulose are common pad materials that always have life of one to three years. Approximately one sq . foot of pad are is needed for 20 square ft of floor area.