Best underground Pipe for outside wood boilers?

[AZBP]

What is the best underground pipe for outside wood boilers; Thermoplex from Central Boiler @$13.95 per ft, Pex-Flex from Urecon @ $9.75 per ft or Flexsul-seal from EZ Burn Mfg @ $12 per ft ? I am going to need about 500 ft and want to make sure I do it right. From their websites, thermoplex and Pex-flex seem to be the same type. I have heard good things about Thermoplex but the Pex-flex is cheaper. Has anyone heard any good or bad things about pex-flex or flexsul-seal?
Thanks for the help.

 

[leaddog]

https://www.hearth.com/talk/threads/26572/ In the above link I point out a DIYS system that is cheaper than Thermoplex and etc. It'd getting late to do it now but if you have a long run it might be worth it. Also with such a long run you might get a contractor foam it.
leaddog