What is EVOH?
Pressurized Systems Must Use EVOH
EVOH pex piping contains an oxygen barrier laminated to the pipe surface. This barrier with protect closed systems from oxygen intake that could result in potential rust and/or damage. Oxygen barrier or EVOH in needed for pressurized systems only. Visit this link for more information: http://www.pbpsa.com/eng/tech-pipeoxy.asp
Non-Pressurized System Do Not Need EVOH
For non-pressurized systems a non-oxygen barrier pipe will be suitable, for your system is open and can breathe in oxygen anyway. Chemical additives are used instead to prevent rusting. Most boiler manufacturers sell these additives.
Wikipedia: http://en.wikipedia.org/wiki/EVOH
