I am planning to build a counterflow wort chiller using a hose outside of a copper tube. There are a great variety of lengths and types available commercially and I have read that many commercial solutions are not long enough to chill properly
What is the optimal length for a counter flow wort chiller? It seems that with counterflow, it should not matter whether you are chilling 3 or 5 gallons. Is this correct? Do you just need the correct length to ensure that wort entering at ~200 deg F cools to <=70 deg F by the end?
Are there any particular construction materials and/or designs that work particularly well? I am planning to purchase hose rated to up to 212 deg F, copper tubing, and T (or similar) fitting on each side to separate hose from tubing.
EDIT: What factors affect the flow rate of wort within the chiller?