Control crawlspace fan based on humidity?

My house has a crawlspace and I want to put an exhaust fan in one of the vent panels to pull air through the other vents. I can buy fans that can be turned on by temperature and/or humidity but I don’t want the fan to turn on if the humidity outside is higher than that in the crawlspace. I’m thinking I need just a basic fan that I can plug in which can controlled by a smart outlet that’s near it in the crawlspace.

I push data from my weather station to Weather Underground so I can get the local humidity using a WU API. I’ll need a device that reports humidity that I can place in the crawlspace, probably reasonably close to an access panel because batteries will need to be replaced.

I’d like to create a routine that polls the crawlspace humidity sensor on a schedule I set and if the humidity is higher than a threshold and the outdoor humidity is lower, run the fan. Then turn the fan off after a specified time period or when the crawlspace humidity gets below the threshold.

Does anyone have any suggestions about the best way to implement this and about a humidity sensor?


Unless things have changed, there is a smart app in the marketplace section of the mobile app under climate control called “smart humidifier” which will let you do exactly this. You just check one sensor for humidity and then you can turn on or off any device which presents as a switch. So that would include the smart pocketsocket that you have the fan plugged into. Or If you need a more complicated rule structure, you can always use webcore.

As far as a good humidity sensor, depends how accurate you want it to be. Many of the inexpensive open/close sensors also have humidity readings. So do most of the multi sensors. Or you can go to something specifically made for that purpose which will be more accurate, but also more expensive.

Thanks for your quick reply. I see the smart humidifier app but because of the need to check values of two humidity sensors it looks like I’ll need custom code.

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What is the best accessory which measures humidity?


Thanks a lot Troy, I am looking at the site you mentioned at the moment. Have you used that humidity sensor before? I have one little problem. The moisture inside my crawlspace is increasing all the time. I don’t know what is the problem. Has someone ever faced the similar challenge? I need to solve an issue urgently. Of course, measuring the wetness is good, but what to do next? I am thinking over applying to diversified crawlspace services located not far from my house. Have you ever used the services of similar companies? Do they have any refunds if the situation goes wrong theoretically?

Sorry for the super late reply but yes, I have 2 of these and they work really well