Hello, its my first post here, I had physics long time ago and now composing a system which need some (only probably) calculation. I have a water system containing 200 litres of water, its all in tube system which is vertically stacked, each tube have capacity of 10 litres, so theres 20 glass (thickness 3mm, diameter 50mm, length 150cm (60 inches)) tubes with water, connected with each other so it can circulate thans to heat in the bottom. Theres a condition to hold temperature of the water between 30-35°C (86-95F). I am planning to do it with quartz infrared heater placed underneath (about at least 30 cm under first tube in order to prevent overheating of first tubes near it, there will be life in it!), the quartz heater will be one rod of approx length 50 inches so it nearly covers length of tubes. The question is, how much power do I need to hold temperature? In aqaurium, its said that 300W is enough for 200litres, but aquarium heaters are placed in the water, in our case we are using air as a heater medium. I am pretending the target is somewhere between 300 and 700Watts. If its difficult to imagine whole system I will add picture of it. Thanks for insights, V.