HD-5 Propane: Specification and Price (2026)

When the EIA quotes a residential propane price, the underlying product is HD-5 (high-density, 5% maximum propylene) consumer-grade propane. The specification matters because it is the contract definition: a dealer sells HD-5 unless the customer specifies otherwise, and a national price benchmark is implicitly an HD-5 price.

What HD-5 actually means

HD-5 is defined in the Gas Processors Association standard GPA-2140, with the equivalent ASTM definition in D1835. The headline numbers are simple: minimum 90% propane (C3H8) by liquid volume, maximum 5% propylene (C3H6), and the balance is mostly butane and other light hydrocarbons within tight limits. The HD-5 name comes from those two numbers: H for High purity propane, D for the density implied, and 5 for the 5% propylene ceiling. The full spec also caps residual matter (the high-boiling-point residue that would foul a regulator), sulfur (under 123 ppm by mass, equivalent to roughly 185 mg/m3), water content (effectively dry), and corrosivity (the copper strip corrosion test).

Every commercial propane sale in the US that is not explicitly something else is HD-5. Your barbecue grill cylinder, your home heating tank, the cylinder a forklift runs on, the autogas at a fleet refueling station, the cylinder a roofing contractor uses for a torch-down installation: all HD-5 unless the dealer and customer have separately agreed on a different specification. The reason the specification is so consistent is that the appliances are engineered to HD-5. A residential furnace burner is set up for the energy content and combustion characteristics of HD-5; running it on lower-purity commercial propane risks incomplete combustion, soot, and warranty issues.

Why HD-5 has a single price (mostly)

The Mont Belvieu spot price and the EIA residential survey price are both effectively HD-5 prices, even though neither source explicitly labels them that way. The reason is that consumer-grade propane is the dominant traded grade and the benchmark hubs (Mont Belvieu, Conway) discover price for the consumer grade because that is what most volume is. Off-spec or higher-propylene grades trade separately, typically at a discount of 5 to 30 cents per gallon depending on the specification gap and the regional demand.

The implication for a homeowner reading the EIA average is that the $2.674 per gallon figure for the week ending 30 March 2026 is the HD-5 price. If a dealer quotes meaningfully below the regional EIA average, the question is whether the grade matches. A dealer selling HD-10 (the commercial grade) or off-spec higher-propylene product at a residential price would be unusual but not unheard of, especially in markets with petrochemical-feedstock supply nearby. The dealer is required to label and sell to the specification under NFPA 58 and state propane regulations, but the buyer should ask if the quote is suspiciously low.

HD-5 versus HD-10 commercial

HD-10 is the commercial-grade specification: minimum 85% propane, maximum 10% propylene. The looser propylene ceiling allows refinery and petrochemical complex propane streams that contain more cracked propylene to qualify, broadening the supply pool. HD-10 is acceptable for many industrial uses (forklift fuel, some heating applications, asphalt heating, torch fuel) but typically not for residential appliances rated for HD-5. The price discount for HD-10 versus HD-5 varies but historically runs 3 to 15 cents per gallon depending on regional propylene supply and demand.

A small but persistent market exists for higher-purity propane (say, 99.5% C3 minimum) for specialty applications like carrier gas in chromatography, refrigeration cycles, and some food-grade applications. That higher-purity material typically trades at a 50 to 200 cent per gallon premium and is handled by specialty gas distributors rather than the residential propane channel. It is irrelevant to retail pricing but worth noting for completeness.

What the specification implies for combustion

The combustion heat of pure propane is 91,690 BTU per gallon (gross or higher heating value). HD-5 sits very close to this because the 5% propylene allowance has a similar heating value (84,500 BTU per gallon for pure propylene) and the balance is mostly butane (102,800 BTU per gallon). The net effect is that HD-5 delivers very close to the nominal 91,500 BTU per gallon used in most appliance and energy calculations. The EIA uses 91,452 BTU per gallon in conversion factors for cross-fuel comparison.

This is why the per-gallon propane price translates so directly to per-BTU heating cost. Our propane vs natural gas page and propane vs heating oil page use 91,452 BTU per gallon as the conversion factor; that number is implicitly an HD-5 number. Commercial HD-10 with higher propylene content runs marginally lower (around 90,300 BTU per gallon), which is one reason commercial users sometimes prefer HD-5 for high-throughput heating applications where the small energy density difference adds up over the season.

Odorant and HD-5

By federal regulation under 49 CFR 173.315(b)(1) for transportation and NFPA 58 for storage and dispensing, all consumer-distributed propane is odorised with ethyl mercaptan (typically 1 to 1.5 pounds per 10,000 gallons of propane). The odorant gives propane its characteristic rotten egg smell, so a leak is detectable. This is added to the HD-5 stream downstream of fractionation, usually at the rack or at the distributor's bulk plant. The odorant has no measurable effect on combustion, on the per-gallon price, or on the HD-5 specification compliance, but it is what makes consumer propane safe to handle.

Reading dealer paperwork

A typical residential propane delivery ticket cites the date, the gallons delivered (with temperature compensation, since propane density changes with temperature and dealers compensate so the customer is buying gallons of equivalent mass not gallons of cold or warm liquid), the price per gallon, any service charges, and the grade. The grade is almost always listed as HD-5 or simply propane (with HD-5 implied). If the ticket lists HD-10, off-spec, or anything other than HD-5, the customer should know what they are getting. Most residential dealers will not sell anything but HD-5 to a home customer because of the appliance compatibility issues. A commercial account (a roofing contractor, a farmer, a forklift fleet) may be on HD-10 deliberately.

What HD-5 does not regulate: density

The specification controls composition, not the calorific value to a hundredth of a BTU. Within the HD-5 envelope, combustion energy can vary by roughly 0.5% between batches depending on the actual mix of propane, propylene, and balance butanes within the spec limits. For practical purposes (residential heating, cooking, grilling) this variation is undetectable. For high-precision applications (laboratory carrier gas, calibration burners, some industrial processes) it matters and specialty gas grades exist.

Pricing implications

The bottom line for pricing is that the EIA residential weekly figure and the Mont Belvieu spot figure are both implicitly HD-5 numbers, the residential delivery a homeowner receives is HD-5, and the appliances are engineered for HD-5. The price discount possibilities for moving to HD-10 commercial grade exist but are only realistically accessible to commercial and industrial accounts willing to accept the appliance compatibility constraint. For a residential customer, the published numbers are the relevant numbers. For a commercial account weighing HD-5 versus HD-10, the typical 3 to 15 cent per gallon discount on HD-10 is real but should be weighed against equipment derating and any energy density loss.

Related

• Commercial vs residential propane price per gallon
• Wholesale propane price per gallon
• Mont Belvieu spot benchmark
• Propane vs natural gas price per BTU
• Glossary

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