How the two differ in kind
Both burn cleanly, both run the same kinds of appliance, and they are not interchangeable without changing parts. The difference that drives everything practical is energy density: propane carries roughly two and a half times the energy of natural gas per unit of volume, and it is delivered to appliances at a higher pressure.
The consequence is that a burner designed for one fuel delivers the wrong amount of the other. Appliances are therefore built and shipped configured for a specific fuel, with a CONVERSION KIT — different orifices, a different regulator setting, sometimes different burner components — to change over. Running a natural gas appliance on propane without converting it delivers far more energy than the burner was designed for, and that is a safety problem rather than an efficiency one. Conversion is straightforward when done by a qualified person with the manufacturer's kit, and improvised when it is not.
The second property that matters is density relative to air. Natural gas is lighter than air, so a leak rises and disperses — which is why natural gas detectors are mounted high. Propane is HEAVIER than air, so a leak sinks and pools in the lowest space it can reach: a basement, an inspection pit, a trench, a below-grade plant room. That single fact drives the siting rules for tanks and appliances, the prohibition on propane appliances and cylinders in certain below-grade locations, and the placement of detectors near the floor.
Everything else is logistics. Natural gas arrives continuously through a main and is billed for what you use; propane arrives on a lorry into a tank you own or rent, so you carry storage, deliveries, a delivery access route, and the price you agreed rather than a metered tariff. Which of the two you can have is usually decided by whether there is a main in the road.
The factors that actually differ
Show
| Natural gas | Propane (LPG) | |
|---|---|---|
| Energy per unit volume | The lower of the two — so a given burner needs a larger orifice and more gas flow. | Roughly two and a half times as much, at a higher supply pressure. Smaller orifices. |
| Appliance compatibility | Configured for it at the factory, or converted with the maker's kit. | The same, in reverse. Never run an appliance on the fuel it is not set up for. |
| Density relative to air | Lighter. A leak rises and disperses; detectors go high. | Heavier. A leak sinks and pools in basements, pits and trenches; detectors go low, and siting rules follow from this. |
| Supply | Continuous from a main. No storage, no running out, no deliveries. | A tank, refilled on delivery. You manage the level, the delivery access and the schedule. |
| Availability | Only where there is a main in the road. This decides the question in most rural locations. | Anywhere a lorry can reach, which is most places. |
| Cost | Metered, and generally the cheaper of the two per unit of energy where it is available. | Bought by the delivery, at a price that varies with supplier, contract and season, plus tank rental if not owned. |
| Pipe sizing | Larger pipe for the same heat input, because more volume has to flow. | Smaller pipe for the same input, and a two-stage regulation arrangement from tank pressure down to appliance pressure. |
| Installation cost | A connection to the main, which is priced by distance and can be substantial if the main is far. | A tank, its base, the siting clearances, and the pipe run to the building. |
| Cold weather | Unaffected. | A tank has to vaporise the liquid, and vaporisation rate falls in cold weather and at low tank levels — an undersized tank can fail to keep up in a cold snap. |
| Who may work on it | A registered or licensed gas installer. Not a DIY task anywhere. | Identical, and tank siting is additionally regulated. |
Which one, and when
Choose natural gas when…
- There is a main in the road and connection costs are reasonable — this usually settles it.
- Consumption is high, where the lower unit cost compounds.
- There is nowhere to site a tank with the required clearances.
- Nobody wants to manage deliveries or run out.
Choose propane (lpg) when…
- There is no main, which is the most common reason by far.
- The property is rural, seasonal, or too far from a main for connection to be economic.
- A portable or temporary supply is needed — a site, a caravan, an outbuilding.
- Backup or supplementary supply where a stored fuel is an advantage in itself.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Can I run a natural gas appliance on propane?
- Only after converting it properly, with the manufacturer's kit, by a qualified person — and never by simply connecting it. Propane carries far more energy per unit volume and arrives at a higher pressure, so the orifice sized for natural gas passes a great deal more energy than the burner was designed for. The results range from sooting and a yellow, unstable flame to overheating, carbon monoxide production and component damage. Conversion means changing the orifices, adjusting or replacing the regulator, and in some appliances changing burner parts and the control settings, all according to the maker's instructions for that model. Many appliances are sold convertible for exactly this reason and the kit is inexpensive. What is not acceptable is drilling out an orifice, fitting a generic part, or assuming it will be fine because it lights.
- Why does propane pooling matter so much?
- Because it changes where a leak goes and therefore where it becomes dangerous. Natural gas is lighter than air, so a leak rises toward the ceiling and disperses, and ventilation at high level helps it. Propane is heavier than air: it sinks, flows along the floor like a liquid, and collects in the lowest enclosed space available — a basement, an inspection pit, a drain, a trench, a below-grade plant room — where it can accumulate to an ignitable concentration while the room above smells of nothing. That is why gas detectors for propane are mounted low, why tanks have exclusion zones around openings, drains and below-grade features, and why propane appliances and cylinders are restricted or prohibited in certain below-grade locations. It is a property of the fuel, not a quirk of regulation.
- What size propane tank do I need?
- Enough for your consumption between deliveries, and enough to VAPORISE at your peak demand in cold weather — and the second constraint is the one that catches people. Propane is stored as a liquid and has to boil off to be burned, and the vaporisation rate depends on the wetted surface area inside the tank and the outdoor temperature. A tank that is adequate for annual consumption can fail to keep up on the coldest morning of the year, particularly when the level is low, because both the temperature and the wetted area are working against it. So sizing accounts for peak simultaneous appliance demand as well as total usage and delivery frequency, and suppliers size accordingly. The practical rule that follows is not to run a tank very low in winter, which is also when deliveries are hardest to schedule.
- Which is cheaper to run?
- Natural gas, generally and in most markets, per unit of energy delivered — which is one reason connection to a main is worth pursuing where the main is close. The comparison is not quite like for like, though, and two things complicate it. Propane is bought by delivery at a price that depends on supplier, contract, volume and season rather than a published metered tariff, so the effective rate varies far more between customers; larger deliveries and owning rather than renting the tank both improve it. And natural gas carries a standing charge plus the connection cost, which on a property far from a main can be large enough to dominate the entire comparison. The honest method is to price the connection, then compare running costs over the years you expect to be there.
- How is the pipework different?
- Sized differently and regulated differently, both following from energy density and pressure. For the same heat input at the appliance, natural gas needs a larger pipe because more volume must flow; propane needs less, which is why propane runs are often smaller for the same appliances. Pressure is the other difference: propane leaves the tank at a pressure far above what appliances accept, so the installation uses staged regulation to bring it down — commonly a first-stage regulator at the tank and a second stage nearer the building. Both fuels are sized by the longest-length method against the total connected load with an allowance for fittings, and both require materials and jointing appropriate to the fuel and the location. All of it is work for a registered or licensed installer, and the sizing calculations are for planning and checking rather than for doing the job.
- Can I switch from one to the other later?
- Yes, and the cost is in the appliances and the pipework rather than in the fuel. Going from propane to natural gas when a main arrives means a connection, a meter, conversion of every gas appliance, and frequently resizing the pipework upward since natural gas needs more volume for the same output. Going the other way means a tank, its base and clearances, staged regulation, and conversion of the appliances in the other direction. In both cases it is worth doing all the appliances at once, since a mixed-fuel installation is not an option. If a main is expected in the foreseeable future, it is worth telling whoever specifies the appliances, because choosing convertible models and sizing the pipework with that change in mind costs nothing now and saves a great deal then.
- What about running out?
- It is the practical downside of a stored fuel, and it is manageable with a little planning. Most suppliers offer automatic top-up based on consumption history or on telemetry from a tank gauge, which removes the need to watch it; the alternative is monitoring the gauge and ordering with enough lead time, which in winter can be longer than expected because everyone else needs a delivery too. Running a tank completely empty is worse than an inconvenience: air and moisture can enter the system, appliance pilots go out, and in many jurisdictions the supply must be pressure-tested and the appliances relit by a qualified person before it can be used again, which is a call-out rather than a refill. Keeping a working reserve is therefore cheaper than the alternative, quite apart from the cold house.
- Is one cleaner than the other?
- Both are clean-burning compared with oil or solid fuel, producing little particulate and no ash, and the differences between them are modest. Per unit of energy released, propane's carbon emissions are somewhat lower than oil's and broadly comparable to natural gas's, with the detailed figures varying by the accounting method and by what is counted upstream — which for natural gas includes leakage from the distribution network and for propane includes delivery by road. Neither is a low-carbon fuel in the sense that matters for a building being designed today, so a decision framed around carbon is usually really a decision about whether to burn anything at all, which points at a heat pump rather than at the choice between these two. For an existing gas or propane installation, the emissions difference is not the deciding factor.