I’m looking to buy a wort chiller for my 7.5 SS brew pot, is a copper or SS wort chiller better?
Copper’s the material of choice. Better heat exchange and the yeast appreciate a few extra copper ions, as I understand it. I suspect it’s more prone to damage, should it get smashed behind something, but can’t say I’ve actually made the comparison.
If you run the equations for a heat exchanger in a liquid to liquid situation like we have, the SS comes out to be about 89% effective when compared to the copper chiller IIRC.
Edit - everything is the same, just change the material properties of the chiller.
Just remember to drain "all’ the water out out of it if you live in an area where it freezes. Ruined one like this when I forgot to drain it. I got in the habit of storing it up-side-down so it will always drain. Yeah, copper works better given the same amount of surface area and mass.
Copper is also easier to work with. As always, design is all about compromise.
I’m assuming you are talking about buying an immersion cooler. I think the benefits of higher heat conductivity is greatly overstated since most of your heat transfer resistance comes from the lack of circulation of wort. I would go with the cheaper cooler all other things being equal.