transfering heat from wood chip pile

What are my options  too transfer heat from my  wood chip pile too xxxx
  Would copper  be my best option?   What other choices do i have

I think you might do well to check out edible acres. Sean has used hot compost piles to heat some spaces in the past. I think you'd find the greenhouse he built attached to his house the most relevant. At least once, he put a stock tank inside and a big hot pile just outside. While building the pile, he built in a coil of what I think was either PEX or garden hose. Both ends ran to the stock tank, one end got a pump attached. The water circulated through the pile and returned, bringing heat inside the greenhouse, as I assume you have in mind. He also does some experiments with moving hot air from a low tunnel underground to raise the average temp, and hot compost piles inside a high tunnel to warm the air directly. Both could be of interest.