Something that just occurred to me, using copper pipe. put sand into it to prevent crushing, and wrap it around the riser put both ends into an open 55 gallon drum. make sure the exhaust is higher than the intake. the boiling water should create a siphon effect. causing it to create a heat sink in the drum and you can water your plants with the warmed water use a thermostatic controller to prevent scalding your crops. I see what you are doing. but wonder about how you are going to keep your soil at 75F for proper growth.
