Model B: Damp weather humidistat, mounts behind an intake vent, opposite the side where the power vent is mounted. Power vents stay off when the humidity is above the setting. The vent turns on when humidity is below the setting or if there is a quick rise in humidity, so that the unit turns off when it is raining.

Model C: Turns unit on when humidity in crawl space rises above a pre set limit, usually set at 50% humidity.

The difference between the 2 controllers is the conditions that they shut off. The HUB (damp weather shut off) is recommended to be set at 75% RH. The operation of it will cause it to shut down at any RH above the set point. The HUC is the opposite, it will turn on at any condition above the set point. Operation is such that the 2 controllers when plugged together in series will maintain the humidity in the crawl space between the set points on the controllers.

For example, the HUB set at 75% and the HUC set at 40% will run at anytime the crawl space has a humidity below 75% and above 40%. If the humidity drops below 40% the HUC will shut off and the fan will no longer run. If the humidity in the space goes above 75% the HUB will shut off and the fan will no longer run. The HUB is intended to be placed in the airstream of the incoming outside air, therefore, if it is raining or humid out and the fan comes on and starts bringing in air above the HUB setpoint (75%), the HUB will turn off and the fan will stop.

The obvious down side to this is that if the crawl space rises above the setpoint of the HUB, the fan will not turn on. However, without the HUB, the HUC would turn on at anytime the crawlspace was above its setpoint and run the fan, it could very well bring in more humid air than is already in the crawlspace, such as when it was raining outside.

The Humidistat / Thermostat system can be used to control up to 6 power vents at one time.

Price:  $91.44