The typical plastic piping materials for ground loop piping systems are:
- HDPE: High-density polyethylene
- PEX: Crosslinked polyethylene
- PE-RT: Polyethylene of raised temperature
- PP: Polypropylene
PP Polypropylene Pipe (types: PP-R and PP-RCT) is typically used as distribution manifolds which may be installed in a vault or indoor mechanical room or as buried system headers.
In addition to these ground loop piping materials, CPVC (chlorinated polyvinyl chloride) may also be used for interior piping, such as headers and manifolds, when approved.
Please see PPI MS-7 Model Specification for Plastic Piping Materials for Ground Source Geothermal Applications for language related to HDPE, PEX, PE-RT, and PP pipe and tubing materials, fittings, and joining procedures. Installation and pressure testing recommendations are also provided.
Note: The term “tubing” typically refers to products where the actual outside diameter (OD) is 1/8 inch (0.125”) larger than the nominal size, the same as copper tube sizes (e.g., ¾ NTS). The term “pipe” typically refers to products where the actual OD matches that of steel pipe of the same nominal size, otherwise known as Iron Pipe Sizing (e.g., 4 IPS), or products in which the actual OD matches the nominal size directly (e.g., 63 mm). In both cases, specified tolerances apply, as per relevant standards.