HD-5 — the residential standard
HD-5 (Heavy Duty 5) is the US standard residential propane grade defined by ASTM D1835. Specifications include:
- Minimum 90% propane content
- Maximum 5% propylene
- Strict limits on butane, ethane, methane, sulfur and water
- Vapor pressure specification ensuring consistent regulator performance
All major US propane suppliers sell HD-5. The grade is intended to provide consistent burning characteristics across appliances and across the country.
Why grade matters
Off-spec propane causes problems:
- High butane content: appliances may not work in cold weather (butane has higher boiling point)
- High propylene content: rubber seals and gaskets degrade faster
- High sulfur: corrosion of regulators, valves, appliance components
- High water content: regulator freeze-up in winter
- Inconsistent vapor pressure: erratic appliance flame heights and performance
Alternative grades
- Commercial Propane (HD-10) — looser specification with up to 10% non-propane content. Used for industrial heat and some commercial applications.
- Propane-butane blends — common internationally, rare in US residential markets
- HD-5+ or Specialty grades — tighter spec for motor fuel and specific industrial uses
Verifying grade
Reputable US dealers supply HD-5 by default. If you suspect grade issues (appliances misbehaving, regulator freezing repeatedly), you can request a certificate of analysis from your dealer documenting the propane spec. This is rarely needed for residential customers but available.
FAQ
Are all US dealers selling HD-5?
Essentially yes for residential delivery. HD-5 is the de facto US residential standard. Industrial and specialty applications may use other grades — but residential bulk delivery is HD-5.
Can low-grade propane damage my appliances?
Yes, over time. High propylene degrades rubber seals; high sulfur corrodes metal components; high water content causes freezing. If you suspect grade issues, request a certificate of analysis from your dealer and consider switching if results are off-spec.