The important thing to know here is the heat capacity of running water. 1 BTU =1 pound of water changing 1 degF. A gallon of water weighs close to 8 1/3 pounds, so the harvestable heat is 8 1/3 BTU per degF per gallon. This will tell you how much water (at the very least) you need to flow to move your heat.
The heat flow follows Fourier's law of thermal conduction. If you buy copper tubing, the manufacturer publishes tested specs for it. Do a little math and find out if you are in the ballpark as far as surface area and flow rate.
