Wort chiller question

Ok, since I'm bottling this weekend I need to prep for my next batch. Just ordered 50' of 3/8" copper tubing from CopperTubingSales.com :: ICS Indsutries :: (who apparently can't spell indSUtries) to make my own immersion chiller, since it seems I can make a 50' chiller for the price of buying a 25' one on eBay.

So I had a thought, should I make a 50' chiller or two 25' chillers so I can prechill with ice water? I have no idea what my cold water temp is but I figure that, even if it's pretty low, it's still better to get a large thermal gradient between chiller and wort than to increase surface area.

Please, if you respond with math and include your working make sure you also include the answer so I don't have to think to much. My brain is full.

Oh yeah, I'm in Northern CA and I doubt my summer cold water is really cold. Oh wait, I think I may have just answered my own question. :cross:

I say make two. By the time the chiller water has made its way through the 50', it has probably lost any ability to transfer heat. My 25' starts out hot as hell coming out the other end, so it has already lost most of its ability to cool the wort.

Also, here in TX I'm dealing with the same warm ground water issues as you, I have switched from a pre-chiller, to a small pump to pump ice water through. The pre-chiller wasn't as effecient as I had hoped.

I start w/ 2 5gal buckets of tap water. Once those have gone through it is cooled pretty well, and I switch to ice. 1 more 5 gal bucket full of ice water, and a couple extra bags of ice. I recycle the water coming out of the chiller once it is cool enough, and just add ice to the bucket the water is being pumped from. I can get down to about 45F for lagers, in about 25 minutes.

+1 on making 2. I wish i had made too because even with a 15 gal boil, a prechiller would be much nicer to have. I made a 25 ft chiller and im going to make a 35 or 40 ft chiller and use my previous one as a prechiller.

make 2 and sell one to another homebrewer.