Kevin, I think you're absolutely correct. Most of the books I read when I was coming along were for people with greenhouses. Even the Rebecca Northen "Home Orchid Growing" assumed that the home grower was using a greenhouse! And sadly, many of the newer books have just translated practices that were valid for greenhouse growing without saying much about the whys and wherefores. The worst reason (in my own orchid society) for using a fan I ever heard was because that's what they get in nature. What tiarella said about breaking up air and providing slight movement is very valid - no one contests that orchids dislike stagnant air. But there's a huge difference in fanning your growing area so the little leaves wiggle the way they tell you to do it in books, and providing a little gentle air movement in the entire room. This is why Jack Kramer suggested that natural currents would probably be sufficient. He seemed to understood our tendency to overdo. So truth be told I put a small circulating fan on unless humidity is really awful, but only to provide the slightest movement of air in the overall room. The higher the humidity the more air movement I provide. And in my space it almost never amounts to fans blowing directly onto plants or enough even to move the thinner leaves of an oncidium. What I do is suspend a length of thin twine over the edge of my light fixture, hanging down to the level of the plants. If that moves a little, that's enough air movement for moderate humidity. To see leaves move, you want humidity at least 60-65% I'd say. John

farminggreen: Presuming your use of the term "aquaculture" means growing fish for the table, unless you live in an area that never drops below freezing, I would have grave reservations about using aquarium heaters to raise water temps high enough to radiate sufficient heat to serve as space heaters, without heating the water to a degree that would kill the fish. Also, aquarium heaters are not really made to raise water temps much over 10 - 12 degrees above ambient air and why every Discus breeder I know has to use multiple heaters in their larger tanks, or risk having their 90 deg. loving fish keel over in winter, even with room temps in the 70s. I suppose it could be done, but you could end up spending far more on the heaters and electricity to run them than if you simply installed a space heater in your GH. So it's really a case of your expected air temps and the volume of warm but not hot enough to kill the fish water necessary to radiate enough heat to warm your GH. However, also keep in mind that regardless if baseboard, old fashoned cast iron stand ups, or underfloor- radiant heat circulates hot water or oil in a closed system. Fish need as much open surface as possible, which also accelerates both evaporation and heat loss. The cooler the ambient air in relation to the tank, the faster it will evaporate and require topping off, and the more wattage to maintain the optimum temp. for the health of the fish.

I needed more than 600 cfm, and the next size they offered was 1200 cfm (two 600's working together). That's internal blowers venting straight out the back, so there isn't really a drop off in amount of air moved like one would get for extended ductwork. There's a continuous speed control knob. I don't know what the lowest volume is, but I'd guess, comparing my previous hood, that it's in the range of 450-650 cfm. If I'm just stirring up a simple sauce, sauteing an onion or boiling up steamy stuff, I run my hood pretty low. Partially that's for the noise, but really it's all that's needed. If there isn't any steam or smell going around the house, that's all I care about. For frying, boiling down stock, or cookingpalooza for the whole gang, I run it at medium high to high. Medium high is usually enough unless I have all burners going. If there's a correlation to how far I turn the knob it's probably around 900-1000 cfm. I don't have a make-up air system. The experts didn't think it was necessary given the particulars of my house. There's little opportunity for backdrafting, though I have sometimes wondered about the pressure thing. When I have run it at full power, I have sometimes felt that the oxygen was being sucked out, but that might well be part neurosis and part from having dozens of people inside with the doors and windows shut and damp out (which is why the shut doors and windows). At that point, the gas burners and the ovens are heating the kitchen anyway, so I'll just open the little casements in my garden window (like wing windows on an old sedan). There isn't a lot of in-sucking at the windows, however, so I think it's more the people breathing the air rather than a real problem with vacuum/pressure. The house is insulated but not air tight. Hope this helps.

Russ, Not sure who you are asking but I am in the Atlanta area. I don't have a greenhouse since I moved - just use my basement for winter care - run 86 or a few more shop lights and could use a lot more for optimum growth. My old greenhouse did have its issues as you mentioned - had roof vents but only two out of four worked. In summer I moved everything outdoors except cactus and succulents as they basked in the heat and drier conditions. The greenhouses I showed above are commercial grade and I guess they have the roof painted with something to lessen the UV rays or maybe some kind of shade cloth? Never gave it much thought since it is bright and very HUMID! They grew a lot of plants in hanging baskets to grow more on the benches below. One of the prop rooms showing fan at the end. The only time my wife accompanied me to a begonia buying trip for our local branch's annual sale. The mother plants grow to enormous sizes due to the bright light of Orlando. A mother plant of Judy Cook that I bought filled half my back seat in my truck. A plant for sale more plants for sale - biggest size they grow - 8 inches. A row of commercial greenhouses before we go into the sauna...