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.

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