A reader writes: I was talking with a friend the other day and he said that he heard that closed-loop systems only last about 10 years because the ground temperature equalizes after several years as a result of so much heat being removed. He said that after 10 years the ground no longer maintains its average ground temperature of 55 degrees F. I have never heard of that before and scientifically that doesn't make any sense to me. I'm guessing you've come across this argument before?