Is 20' of copper enough?

I know this question has been asked before, but I have seen many conflicting answers and just wanted to get an up to date opinion.

I want to build an immersion wort chiller. The problem, HD and Lowes only sell 20' lengths of copper. I want to know if this will be sufficient. I am about to start doing all grain 5 gal. full boils.

Couple of details:
The kettle I want to get is 13.5" wide by 15" high
I live in New Jersey, so tap water temps aren't too high

25 ft is the minimum I would go. You can get a 50ft coil online and then you're all set for double batches. My 50 footer works great for single and double batches.

With IC's, the key factor is the chilling water temp. A twenty footer will likely work fine in the winter months. During the summer heat, tap water temps can be so warm that a 50 footer won't get you as low as you would like. Twenty is likely too samall as you also have a foot or aso at each end that is not in contact w/ the wort.

I use an IC made from 20' of pipe that i picked up at HD. During the winter it chills 5 gallon batches no problem. During the summer I use the tap water to cool the wort down to 150-160 degrees and then recirculate ice water to chill it the rest of the way.

Its all about having a sufficient temperature gradient increased surface area makes the chiller more efficient though.

I used the same 20' copper from HD. I made a coil around a bucket I had and used some solid copper wire to hold the coils together. I found that when the IC is set on the bottom of my pot it is only half as tall as it should be. If I had to do it again I would use the 50' To make sure the coil goes from the bottom of the BK to the top of the wort. If you use the 20', try to space out your coils to get better spacing in your pot without having to hold it.

The performance has been fine but I have to hold it in the middle of the pot. For my last batch I cooled 5 gal to 70F in under 20 minutes, but I was in my garage in Chicago and it was about 35F outside.