Just realized I never did a wrapping-up post for this thread. I ended up replacing the 440 CFM fan with a 1700 CFM fan, and have a single 12" passive intake. As soon as the (outside) overnight lows consistently stay above ~50°F I’ll also be swapping out the glass on the far door for the screen panel that the door came with to improve air flow. That setup seems capable of maintaining a delta of about 14°F relative to outside temperatures, which should be sufficient here in Seattle.
As for heating, the 1.5kW heater can maintain an overnight delta of just over 15°F, which should be enough for my purposes (though perhaps costly next winter). It’s been almost a month since the heater had to work full strength, though. Mostly now it turns on for a few minutes every 45 min overnight.
It’s been overcast recently, so the weekly average shows what a typical overcast late spring day looks like, while this morning is only partly cloudy so the fan already turned on a little while ago:
My avocados are all flourishing, and for anyone curious about that ongoing project, I have a separate thread just for that purpose:
Thanks again to everyone for the tips/suggestions/feedback in this thread, my greenhouse wouldn’t be the success that it is without your help!
