Chemistry and properties
- Propane is C3H8 — a three-carbon hydrocarbon
- Boiling point: -44°F at atmospheric pressure
- Vapor is 1.5× heavier than air (pools low when leaked)
- Storage pressure: ~120 psi at 70°F
- Energy: 91,500 BTU per liquid gallon
- Liquid propane = 1/270th the volume of vapor (efficient storage)
- Combustion range: 2.1–9.5% propane-in-air concentration
Sourcing and market
- ~2/3 of US propane comes from natural gas processing
- ~1/3 from crude oil refining
- The US is the world's largest propane exporter (since ~2014)
- Mont Belvieu, TX is the US wholesale propane benchmark
- EIA Weekly Heating Oil and Propane Survey is the authoritative US price source (Oct-Mar)
- Residential propane is sold per gallon; commercial often per pound
US residential market
- ~12 million US households use propane for any application
- ~5 million use it as primary heating fuel
- About 5% of US households heat primarily with propane
- Standard residential heating tank: 500 gallons aboveground ASME
- Tanks are filled to 80% (thermal expansion margin)
- Most US tanks are leased from the dealer
Safety
- Odorized with ethyl mercaptan (rotten-egg smell) by US law
- NFPA 58 governs storage, transport and installation
- CETP is the industry-standard technician certification
- After run-out, NFPA 58 requires licensed leak test before relight
- Carbon monoxide from incomplete combustion is the dominant lethal hazard, not propane itself
FAQ
What's the most important propane fact for a homeowner?
Probably the odorization fact. Propane is odorized so you can detect leaks by smell — knowing what that smell is and the LEAVE-SHUT-CALL procedure prevents almost all serious incidents.
How does propane compare to natural gas as a fact set?
Propane has higher energy density per cubic foot (2.4×) but the same approximate cost per BTU at typical 2026 US prices. Natural gas wins on cost where available; propane wins on universal availability via truck delivery.