Propane and natural gas are both gaseous fuels used for heating, cooking, and water heating, but they are different products with different delivery models, energy contents, and economics. The choice between them is rarely a real choice — it is determined by whether your property has natural-gas utility service available at the curb. Where both are options, the numbers favor natural gas.
Side-by-side
| Factor | Natural gas | Propane |
|---|---|---|
| Primary molecule | Methane (CH₄) | Propane (C₃H₈) |
| Delivery | Utility pipeline | Tank truck → on-site tank |
| Stored as | Pressurized pipe gas | Liquid in a pressurized tank |
| Energy content | ~1,030 BTU / cubic foot | ~2,500 BTU / cubic foot |
| Energy per gallon (liquid equivalent) | n/a | ~91,500 BTU / gal |
| CO₂ per million BTU | ~117 lb | ~139 lb |
| Burner orifice | Larger | Smaller |
| Service interruption | Rare; utility-managed | Tied to scheduled deliveries |
| Available in rural areas? | Often no | Yes |
| Typical delivered cost | Lower per BTU when available | Higher; truck delivery overhead |
The energy-density difference is the most important practical fact. A propane appliance burns through less than half the volumetric flow of a natural-gas equivalent because each cubic foot of propane carries about 2.5× the heat. That difference is why every fuel-flexible appliance ships with two sets of orifices — one sized for natural gas, one for propane — and why an unconverted natural-gas appliance over-fires on propane and an unconverted propane appliance under-fires on natural gas.
Equipment compatibility
Most modern furnaces, water heaters, ranges, dryers, and boilers ship dual-fuel-rated: the same chassis is sold either factory-set for natural gas or with an LP conversion kit included for propane. NFPA 54 governs how the conversion is performed:
“The appliance shall be connected to the fuel gas for which it was designed. No attempt shall be made to convert the appliance from the gas specified on the rating plate for use with a different gas without consulting the installation instructions, the serving gas supplier, or the appliance manufacturer for complete instructions.”
NFPA 54 / ANSI Z223.1, §9.1.3 (Appliance connection to fuel gas — National Fuel Gas Code, 2024 ed.). View source
In practice that means a licensed installer using the manufacturer's LP kit swaps orifices, adjusts the gas-valve regulator output pressure, and verifies combustion analysis at startup.
Older equipment — pre-2000s gear, some commercial models — is built for one fuel only. Field-converting a single-fuel appliance is manufacturer-dependent: some publish a conversion procedure, others treat the appliance as not convertible.
Cost
When natural-gas service is available at the curb, natural gas is nearly always cheaper per delivered BTU than propane. The pipeline delivery model has lower marginal cost than truck delivery. The EIA publishes regional residential prices for both fuels; most regions show natural gas running roughly half the per-MMBTU cost of delivered propane.
When natural-gas service is not available, the comparison flips entirely:
- Extending a utility line typically costs $50–$200/foot in capital, paid by the homeowner.
- A natural-gas service connection that requires a 500 ft extension starts at $25,000.
- Propane infrastructure (tank + regulator + supply line) for the same home is in the $1,500–$5,000 range installed.
For any home outside utility-service range, propane is the answer that makes financial sense even if the per-BTU cost is higher.
Environmental and emissions
Both fuels burn cleanly, with very little soot or sulfur compared with oil or wood. At the burner, natural gas emits the least carbon dioxide of the common fossil fuels, about 117 lb of CO₂ per million BTU versus roughly 139 lb for propane (EIA carbon coefficients). On combustion alone, natural gas is the lower-carbon choice.
The full picture is closer than those numbers suggest. Natural gas is methane, itself a potent greenhouse gas: methane traps far more heat than CO₂ over both 20- and 100-year horizons, so leaks during production and pipeline distribution add to natural gas's lifecycle footprint. Propane is not methane and does not carry that leakage penalty. Released propane is not a significant greenhouse gas, though it is a flammable vapor that is heavier than air and pools low, where natural gas is lighter than air and disperses upward.
Neither fuel contains meaningful sulfur, and both produce far lower particulate emissions than heating oil. The EPA recognizes propane as an approved clean alternative fuel under the Clean Air Act Amendments of 1990.
Reliability and resilience
The two fuels have different failure modes:
- Natural gas is utility-delivered. Service interruptions are rare but, when they happen, affect entire neighborhoods at once and require utility action to restore.
- Propane is on-site storage. There is no utility to fail — whatever is in your tank keeps running through any storm or grid event — but you depend on your supplier's delivery cadence to refill the tank.
For backup-power generators, propane is the dominant fuel specifically because of this property: an extended outage that takes down the grid also takes down the natural-gas compressor stations on a long timeline, while propane stored on-site keeps the generator running until the tank empties.
Which fits which home
- Natural-gas service at the curb: take it. The long-run cost advantage is real and the delivery model is hands-off.
- Rural or off-grid: propane. The line-extension cost makes utility natural gas a non-starter.
- Mixed neighborhoods at the edge of utility service: get a written quote from the utility for line extension, compare it to the payback on switching to propane, and remember the utility rate is regulated and you can't shop it among providers.
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Frequently asked questions
- Are propane and natural gas the same thing?
- No. Both are gaseous hydrocarbons used for heating, but they are different molecules. Natural gas is mostly methane (CH₄); propane is C₃H₈. Natural gas is delivered through a utility pipeline as a low-pressure gas. Propane is delivered as a pressurized liquid that vaporizes in your tank regulator on the way to the appliance.
- Which has more energy, propane or natural gas?
- Propane is more than twice as energy-dense by volume. A cubic foot of propane vapor contains about 2,500 BTU; a cubic foot of natural gas contains about 1,030 BTU. That means a propane appliance burns less than half the volume of a natural-gas appliance to deliver the same heat — which is why propane orifices and burner jets are smaller than natural-gas equivalents.
- Can I use a natural-gas appliance on propane?
- Only if it is converted with the manufacturer-supplied LP conversion kit, which swaps the burner orifices and adjusts the gas valve to handle propane's higher pressure and energy density. Many modern furnaces, water heaters, and ranges ship dual-fuel-rated; older appliances and some commercial equipment are field-converted by a licensed technician. Running an unconverted natural-gas appliance on propane creates an over-firing condition and is unsafe.
- Is propane or natural gas cheaper?
- It depends on your region and the time of year. Natural gas — when you have utility service — is almost always cheaper per BTU than delivered propane, because pipeline delivery has lower marginal cost than truck delivery. Propane wins in any home that does not have natural-gas service: extending a utility line is often $50–$200/foot in capital cost, which dwarfs years of fuel savings.
- Can I switch a natural-gas home to propane?
- Yes, but it is more common to go the other direction (propane → natural gas) when utility service becomes available. Switching from natural gas to propane requires installing a tank, the regulator and supply line, and converting every gas appliance with the appropriate LP conversion kit. The driver is usually a utility outage, a remote second home, or a desire for backup capacity behind the natural-gas service.