Natural Gas vs Propane Standby Generator: Which Fuel?

Natural gas runs cheaper and never needs refilling; propane works anywhere. How the fuel choice changes install cost, runtime and reliability.

Most standby generators from the major brands run on either fuel — the same unit ships with a selector or a simple conversion. So this isn’t a question of which generator to buy; it’s a question of which fuel makes sense for your house. For most homes the answer is decided by one fact: do you have a natural gas line?

The short version

If you have natural gas

Use it. You never refill, never think about it, and the running cost is lower. The install question is whether your existing meter can supply the generator’s demand on top of your furnace, water heater and stove. A 20 kW unit can draw 200–300 cubic feet per hour at half load. If the meter is undersized, the utility upgrades it — sometimes free, sometimes a few hundred dollars, and it can add weeks to the schedule. Have the installer check this on the site visit, not after the unit is on the pad.

One caveat: in a large regional disaster, gas systems can go down too. It’s rare, but if your outage risk is earthquake or major hurricane rather than ice storms and summer thunderstorms, propane’s independence from any utility is worth weighing.

If you don’t have natural gas

Propane it is. You’ll need a tank — typically 250 to 500 gallons for a whole-house unit, buried or above-ground, purchased or leased from a propane supplier. Many suppliers lease the tank cheaply if you commit to buying fuel from them.

Sizing the tank is about runtime. A 20 kW generator at half load burns roughly 2–3 gallons per hour. A 500-gallon tank (filled to the standard 80%, so 400 usable gallons) gives you in the region of five to eight days of continuous half-load running. If your outages are measured in hours, a smaller tank is fine. If you’re planning for a multi-day event, size up — and remember that propane deliveries are slow after regional storms because everyone else is calling too.

What it does to the install price

Either way you’re paying for a fuel line from the source to the generator pad, typically $500–$1,500 depending on distance. Natural gas may add a meter upgrade; propane adds the tank (a few hundred dollars a year to lease, or $1,500–$3,000+ to buy and bury). Over the life of the system natural gas is cheaper if you have it; if you don’t, the cost of bringing a gas line to a house that lacks one is almost never worth it just for a generator.

Diesel?

Diesel standby units exist and are common in commercial settings. For a home they’re louder, need fuel that degrades in storage, and cost more to buy. Unless you already have diesel on site — a farm, say — it’s not the residential answer.

Bottom line

Have natural gas? Use it, and confirm the meter. Don’t? Propane, and size the tank to your realistic outage length. Ask installers to quote the fuel connection as a separate line so you can see exactly what you’re paying for. See the full installed cost breakdown →