Insulated Pipe
Underground, insulated piping systems are used for Hydronic heating applications including corn burning boilers, wood boilers, solar, geothermal and other water transfer systems.
Here is a link to some information on the what and why of Insulated Pipe.
We sell two different lines of insulated pipe. Both are fine products, either may be suitable for your situation. GTGlobe Industriesand eZe-Flex
Theses prices are very competitive. REMEMBER, you don't pay shipping when you ship to a location that has a fork-lift or a loading dock.