Propane vs Natural Gas for a Standby Generator

Natural gas means no tank, no refills and no fuel that can run out mid-outage, at the cost of a slightly lower output rating and a dependence on the gas main reaching your property at adequate pressure. Propane carries more energy per gallon, does not degrade in storage and works anywhere, but the tank is finite, and getting a delivery during a regional event is the part people underestimate.

For a lot of the properties we work on, the decision is already made. Much of rural Parker and Palo Pinto county has no piped gas service at all.

Start with what your property actually has

The Railroad Commission of Texas publishes a table of natural gas service to Texas cities with meter counts by community. It settles this question town by town, and the picture around here is not what people assume.

Brock, Annetta, Peaster, Poolville, Cool, Garner, Dennis and Tin Top have no investor-owned gas distribution utility listed at all. Santo has none either. Willow Park, a city of nearly five thousand people, shows 130 residential natural gas meters, which means the overwhelming majority of homes there are on propane or all-electric. Weatherford and Aledo are genuinely gas towns, and even in Weatherford the residential meter count sits well below the number of households.

The Census Bureau’s house-heating-fuel data says the same thing from another angle: Palo Pinto County households are around seven times more likely than Tarrant County households to heat with bottled or tank gas, and Erath County is not far behind. Propane is not a fallback out here. For a great many properties it is the normal answer, and any generator content that treats natural gas as the default was not written for you.

Natural gas: the case for it

When it works, it is the easier ownership experience by a distance.

• No tank to fill, monitor or site. No delivery schedule, no gauge to check, no decision about whether to top off before a forecast. The fuel is simply there.
• Effectively unlimited runtime for as long as the distribution system holds pressure. On a multi-day outage that removes the single largest constraint.
• No tank clearance to design around. One less setback competing with the septic field, the well and the property line for the pad location.
• Fuel cost lands on the utility bill rather than as a delivery invoice.

The catch is supply capacity. A standby generator is a large gas appliance, and the question is not whether gas reaches the house but whether the meter and the piping can feed the generator at the pressure it needs while the furnace, water heater, range and dryer are also drawing. That is a calculation, not an assumption, and it is one of the line items covered in what a generator costs in Texas.

This is why a long run to a pad across a pasture is a real cost, and why an installer who has not asked where the meter is has not priced your job.

Propane: the case for it

Propane carries roughly 91,500 BTU per gallon, which is a lot of energy in a small footprint. It does not go stale, gum up or separate the way gasoline does, so a tank filled today is still good fuel in five years. And it is completely independent of any distribution network, which is the whole point on a property with no main.

• Available anywhere. Twenty acres past the end of the gas line is not a problem.
• Higher output from the same machine. Units are typically rated a little higher on propane than on natural gas.
• Indefinite storage life. Unlike the fuel in a portable generator’s can, it is ready whenever you need it.
• You control the supply. A full tank before a forecast event is a decision you can make. Nobody can make that decision for you on a gas main.

The trade is that the tank is finite, and refills during a regional event are the genuine risk. When an ice storm takes out power across several counties, propane trucks are dispatching to everyone at once, over the same roads that are causing the outage. Plan for the tank you have, not the delivery you hope for.

How long a tank actually lasts

This is the number people want, and it is knowable within a useful margin as long as the assumptions are stated. Two things drive it: how much fuel is genuinely usable in the tank, and how hard the generator is working.

A propane tank is filled to about 80 percent of its water capacity, because liquid propane expands with temperature and the vapour space is not optional. A 500 gallon tank therefore holds roughly 400 gallons of usable fuel, and a 1,000 gallon tank roughly 800.

Two lessons come straight out of that table. First, tank size buys days, and doubling the tank roughly doubles the runtime, which is the cheapest resilience available on a propane property. Second, load management earns its keep twice on propane: a managed system that keeps the generator off its ceiling burns less fuel per hour, so the same tank lasts noticeably longer.

The cold-weather failure mode nobody mentions

Liquid propane has to vaporize before the engine can burn it, and vaporization happens at the wetted surface of the tank. Two things reduce how fast that happens: cold ambient temperature, and a low liquid level, which leaves less wetted surface. Run a large generator hard, from a nearly empty tank, in a hard freeze, and it is possible to demand vapour faster than the tank can produce it. Pressure drops, the unit stumbles or shuts down, and the tank is not empty.

This is a solvable design problem, not a reason to avoid propane. It is solved by sizing the tank for the generator rather than for the house, and by keeping the tank reasonably full through winter. It is also the single best argument for 1,000 gallons over 500 on a property running a larger unit.

Owned tanks and leased tanks

If you lease from a propane supplier, the tank is theirs, the set is usually handled for you, and you generally buy fuel from that supplier. If you own the tank, you can shop the fuel, which matters over a fifteen-year ownership, and you carry responsibility for the tank itself. Neither is wrong. What matters for the generator project is knowing which you have before the design, because it affects who does what, where the tank can sit and how quickly the work can be scheduled.

One practical detail people miss: the delivery truck has to reach the tank. A tank set behind a gate that will not open, or at the bottom of a drive that turns to soup after rain, is a tank that gets filled late. Check the approach before you choose the location.

Choosing

Choose natural gas if a main serves the property and the meter and piping can be shown to support the unit at full load. Unlimited runtime with no fuel logistics is the better ownership experience, and it is worth the slightly lower output rating.

Choose propane if there is no main, if the gas supply cannot be brought up to the required capacity at sensible cost, or if you would rather control your own fuel than rely on someone else’s distribution system. Then size the tank for real runtime rather than for the minimum that will start the engine.

Either way the machine is largely the same. Our Generac and Kohler residential units are configured for the chosen fuel at installation, and the fuel work is part of the installation scope rather than something you arrange separately. If you want to know which way your property should go, we can tell you from the meter, the tank and the run, and it takes a site visit rather than a phone call. It also feeds directly into how long the system can actually run once the power is out.