Propylene Glycol Compatibility With Hydronic System Components

Propylene Glycol (PG) is the preferred and most common heat transfer fluid additive used in hydronic heating and cooling applications. It’s ubiquity makes it's cost and availability attractive in comparison to other engineered fluids. And the fact that it’s “non-toxic” makes it a relatively safe choice for most applications, including for food production, food processing, and food service.

While there are conflicting views on the long term compatibility of propylene glycol with certain materials, namely with plastic compounds like PVC & CPVC, PG is still likely to be the best option all things considered. Depending on the application and the lifetime expectancy of the hydronic infrastructure (piping, fittings, etc.) and equipment (pumps, heat exchangers, valves, etc) you may wish to consider a few options:

1. Using alternative heat exchange fluids like ethanol or ethylene glycol
2. Accept a certain amount of preventative maintenance, and/or acknowledge the short term nature of the application
3. Upgrade your materials to more compatible options

Every application is different; different performance requirements, different budgets, and different serviceability needs, etc.. As a system designer, installer, and/or owner, you'll need to balance a variety of considerations in order to arrive at the best combination of features for you. Please keep that in mind while reviewing this short list of recommended materials and components for use with propylene glycol:

• Piping
  • Best: ABS, HDPE
  • Acceptable Long Term¹: Polypropylene, PEX (polyethylene)
  • Acceptable Short Term²: CPVC, PVC
• Distribution & Fittings
  • Best: 316L Stainless Steel, ABS, HDPE
  • Acceptable Long Term: 304 Stainless, Brass
  • Acceptable Short Term: CPVC, PVC
• Controls Valves
  • Best: Stainless Steel, Copper, ABS, HDPE
  • Acceptable Long Term: Brass
• Thermostatic
  • Best: With Well Probe
  • Acceptable Short Term: PVC (AWM 2464 probe sheathing is commonly made of PVC)
• Heat Exchangers
  • Best: 316L Stainless
  • Acceptable Long Term: 304 Stainless, Brass
• Pumps
  • Best: 316L Stainless
  • Acceptable Long Term: Cast Iron, ABS, HDPE, PTFE
• Pump Seals
  • Best: Buna to 250F
  • Acceptable Reg Temp³: EPDM to 70F, TPO to 70F, Silicone to 70F, FFKM (Chemraz, Simriz, Kalrez)
  • Acceptable High Temp⁴: FKM (Viton) to 140F

¹ Long Term: > 3 Years

² Short Term: < 3 Years

³ Reg Temp: <70F

⁴ High Temp: > 70F