Some folks don't understand that at our northern latitudes, ground temps control basement temps. I fully understand how yours stays cool. It's rare for mine to get above 80F during summer - usually about 70F. When summers are hot, I open a couple basement windows at night and run fans to cool basement and then close windows during day. I figure I can keep less than 75F most summers. Right now, my tank is 72F after lights have run all day and at night will drop to 62F. I congratulate you on the success of your growing and it makes me want to try once I get a few other species figured out
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Ross
http://orchids-ross.blogspot.com/
I don't do most Dendros or large, "floofy orchids". For me it's minis (like Angraecoides), Masdies, Paphs, and others that crept in somewhere along the line. See my orchid list for complete collection (usually not current.)