A pond in your greenhouse may not sound like a good idea, but I am glad I put this in first. Right now it”s perfect for what I need. I”m sure that in the future this will not be enough space, but for now it”s just the right size. It serves many purposes and so far it has not dropped below 45 degrees f. It has it”s own waterfall that runs off a car battery with solar panels to charge it. This is a pretty cool setup cause I have it on a switch and only run it when I”m in there. It”s all about goin green. Very cool and free to run. Fish and plants are happy which in turn makes me happy. I also have some barrels painted black filled with water and the walls and ceiling are well insulated with plastic sheeting. My glazing is glass windows and my roof is vinyl corrugated sheeting. It holds the heat pretty good average nightime lows are about 44 degrees f. Daytime highs as of today 76 degrees f. I still have alot to learn but I having fun doing it. And I”ll be sure to keep you posted and thanks for reading. Jeff