I brew 20 gallon batches. That's 2 X 50' coils of 1/2" copper. The water flow splits between them and then collects again for a single effluent. There are temperature sensors in both the in and the out. It works amazingly well. Of course, I bought the copper at the height of the market from Homer Depot because I was impatient. You could build it for about $100 less right now.