Possibly solved my greenhouse dilemma.

I had hoped that simply having an airway open to the crawlspace under the house, would be enough to maintain a comfortable temp inside the enclosure on frigid nights, which we haven't really had yet, but we've had cold enough temps, that I could see that the temp inside, followed outside but 5° warmer.

So what would happen if it went down to 20°F?
I've had this fan, and I've had the idea to have it thermostatically controlled to automatically come on and off as needed.
Sadly, I've not found such a device. A thermostatically controlled attic fan would be

1. TOO large and
2. blow TOO much air,

so today I found these:

↑Screen shot from their website↑
once linked to my phone:

I can turn them on and off remotely, as long as I am aware of the temps.
There was a problem at first, the wifi wasn't connecting when I had the switch device INSIDE the enclosure, it would turn the fan ON, but not off oddly.
SO

Sitting here at my pc, next to the router at the far back of my house, I can switch the fan on and off

We are supposed to have another 'arctic blast' this weekend, and by all accounts it will be hanging around longer than the 2-3 days of cold we had last week.
updates as they occur.

"Possible Solution?"

^by
Jerry E Smith
©11/17/2021
^{All images original, screen shots from product website}