Okay, so I just purchased and installed a "Mr. Heater" 30,000btu ventless gas heater. I have a fan on low to distribute the heat. I've had it going now for 24 hours, keeping the individual aquarium heaters in operation as a safety net, until I get the temperature stable. Well, checked this morning and all the aquariums (top & bottom) are showing 79 degrees. (Except one fry tank on the bottom that the temp. was off the chart and all the fry were dead, due to a heater that stuck on). So, after composing myself, my wife and I decided that it was time to remove all those &%@! energy suckin' heaters and rely on the ventless heater. Looking forward to my energy bill going down drastically.