The last time I dealt with any physics was 6 years ago in college, so forgive my apparent ignorance: The Situation. I have a swimming pool pump outside near the house's air conditioner unit (heat exchanger I think it's called). Well, the freon is coming out of the house in copper pipes to release heat and be cooled, and the swimming pool water is just begging to be heated. I foresee a match made in heaven. The Idea. What I want to do is build a type of radiator to marry the hot freon with the cold water. If all goes well, this'll increase the efficiency of my air conditioning unit and save me lots of $$$ on a heating system for my pool. I'll be using a large, PVC tank (similar to the one already on the pool pump system) to house the pool water I'm heating. The cool water will come into the bottom and exit near the top. Coiled inside of the tank will be the hot freon-filled copper pipes. The Problem. How big does this thing need to be? How do I calculate the BTU this thing is going to be capable of generating (to determine if this is even worth it)? Is there a better way to go about transferring the heat from the hot freon-filled copper pipes into the water? According to "http://www.fsec.ucf.edu/en/" [Broken] and other Internet articles, it appears I'll need something like 100,000 BTU to raise the temperature of the pool 3 degrees F. So, I think that's my minimum goal. The Numbers. PVC pipe housing the pool water 3" inside diameter ~40 PSI 75 - 83 degrees F unknown water flow rate Copper pipe with hot freon 0.5" inside diameter 110 - 120 degrees F unknown pressure and flow rate Water tank I haven't built the system yet, so this is the major variable I'm trying to determine ... how big, and how much copper does this thing need to have in it? Thanks in advance to anybody who can help me with this problem.