Standby Generator Runtime Cost

I'm installing a new generator — which fuel should I actually choose?

For most homes the decision is nearly made for you by what's already at the property, and the tiebreakers are about resilience rather than price. If you have a natural gas line at the house, that's usually the answer: it's the cheapest per hour at typical utility rates, it requires no tank and no yard space, there's nothing to refill, and it can run indefinitely — which is precisely the scenario that matters, since short outages are cheap on any fuel and long ones are where tank-based systems get uncomfortable. The exceptions worth taking seriously: in seismically active regions, gas mains are shut off after significant earthquakes as a safety measure, so the outage most likely to matter is the one where your fuel supply also stops — that's a genuine argument for on-site propane even where gas is available. Choose propane when there's no gas line (common rurally), when you want fuel independence, or when you already have a propane tank for heating or cooking, in which case marginal cost is just a bigger tank or more frequent fills. Size the tank to the outage you actually want to cover: a 500-gallon tank at its 80% safe fill gives a 22 kW unit roughly six and a half days at half load, while a 1,000-gallon tank roughly doubles that, and tank rental versus purchase is worth pricing both ways with your supplier. Diesel is rarely the right residential choice: the engines are the most efficient of the three and diesel units are extremely durable under sustained load, which is why they dominate hospitals and data centers, but for a house the fuel is expensive per gallon, it degrades in months rather than years (requiring stabilizer, periodic polishing, or scheduled turnover), the units are heavier, louder, and pricier, and they need spill containment. Diesel earns its place when you need long runtime at high load, are already on heating oil, or are sizing above roughly 30–40 kW where liquid-cooled diesel becomes the practical option. One more practical factor across all three: whatever you choose, verify supply capacity with your installer — natural gas installations in particular fail to make rated output when the meter or line is undersized, and a generator starved for gas pressure both underperforms and runs badly.

We're on day four of an outage — how do I stretch the fuel and what maintenance do I owe the generator?

Two jobs here: reduce burn rate, and keep the machine healthy long enough to finish the outage. On burn rate, the highest-leverage move is load management, because efficiency improves as load rises toward the sweet spot but total consumption always rises with load — so the goal is fewer, more purposeful high-load periods rather than continuous partial use. Concretely: run the well pump, laundry, dishwasher, and electric range in deliberate blocks instead of trickling; set air conditioning a few degrees warmer or heating a few cooler; unplug the second refrigerator and any electric water heater you can live without (electric water heating is often the single biggest discretionary draw in the house); and switch off the generator entirely for stretches if your situation allows — modern automatic transfer switches make restarting trivial, and a full refrigerator holds temperature for hours. If you're on propane or diesel, do the arithmetic now rather than at hour 90: divide remaining fuel by the hourly consumption this calculator shows, and if the answer is less than the outage forecast, start rationing immediately, since early rationing buys far more hours than late rationing. Also call your supplier early — during regional events, delivery queues form fast, and being on the list at hour 12 beats calling at hour 100. On maintenance, this is the part owners forget: air-cooled standby units typically specify an oil-and-filter change every 100 to 200 running hours, and continuous operation reaches that in four to eight days. Have oil, a filter, and spark plugs on hand before storm season, and check the oil level daily during a long run — these engines consume some oil under sustained load, and running low is how a generator that survived the storm doesn't survive the next one. Let it cool per the manual before servicing, keep the air intake and cooling fins clear of debris and snow, and watch the exhaust routing stays clear — carbon monoxide risk rises when snow drifts around a running unit. Finally, keep a log of running hours; it's what tells you when the next service is due, and it's genuinely useful information for a future buyer.

Would a home battery be cheaper than running a generator?

For short, frequent outages a battery often wins on operating cost; for long or frequent multi-day outages a generator usually wins on capability, and the honest comparison depends on which failure mode your area actually has. The operating-cost side favors batteries: a battery stores grid or solar electricity and, paired with solar, can recharge daily at essentially zero marginal cost, whereas a generator burns $4 to $7 an hour in fuel whenever it runs. There's no fuel to store, no engine to maintain, no oil changes, no exercise cycle, no noise, and no carbon monoxide. The capability side favors generators, and the constraint is capacity: a typical home battery holds roughly 10 to 15 kWh usable, which covers essential loads for a day or so, or heavy loads for a few hours, and then it needs recharging. Without solar, that means it's simply empty until grid power returns — precisely the wrong behavior in a long outage. With solar, it recharges daily but at whatever rate the weather allows, which is a real limitation during the winter storms and multi-day overcast that cause many outages, and solar output during a snow-covered week can be near zero. A generator, by contrast, produces full output continuously for as long as fuel lasts, and on natural gas that's indefinite. The costs are also structured differently: batteries are expensive up front ($10,000–20,000 installed for a single battery, more with solar) with near-zero running cost, while a standby generator runs roughly $6,000–15,000 installed with real per-hour operating cost. So the decision usually comes down to your outage profile. Frequent brief interruptions, a mild climate, existing solar, or a priority on silence and zero maintenance point toward a battery. Rural service with multi-day outages, well water (no power means no water at all, and pumps are surge-heavy), medical equipment, or serious heating and cooling loads point toward a generator. A number of homeowners with the budget do both — battery for the common short outages and seamless switchover, generator for the rare long one — which is genuinely the most resilient configuration if not the most economical. Worth running our solar battery storage calculator alongside this one to compare the two on your own numbers.

My generator burns noticeably more fuel than this estimate — what explains it?

Several legitimate factors, and one common misreading of the load input. Start with load, because it's the usual answer: homeowners consistently underestimate what their house draws during an outage, and the calculator's 'half load' assumption is easy to exceed without noticing — central air conditioning alone can consume half the capacity of a 22 kW unit, and an electric water heater, electric range, or well pump cycling adds up fast. If your generator is effectively running near nameplate, compare against the full-load figure, which for natural gas is roughly 40% higher. Beyond load: ambient temperature matters in both directions, since cold air is denser (marginally better combustion but a colder engine burning richer during warm-up) and heat reduces air density and output; altitude derates engines meaningfully, roughly 3% of power per 1,000 feet, so a high-elevation unit works harder for the same output; and engine age, spark plug condition, and a dirty air filter all cut efficiency, which is one practical reason to keep up with maintenance during a long run. Gas supply pressure is a frequently missed cause specific to natural gas: an undersized meter, undersized gas line, or a regulator that can't keep up under simultaneous demand from your furnace and water heater will starve the generator, which then runs poorly and inefficiently — if your unit has always seemed thirsty or struggles under load, have the installer verify gas pressure at the generator while it's running under load. Also account for what the calculator doesn't include: the weekly exercise cycle consumes a small amount of fuel year-round, and some fuel is burned during startup and cooldown rather than while producing useful power. Finally, remember these figures come from a model validated against one manufacturer's published data, and manufacturers measure consumption differently with no governing standard — your own unit's spec sheet is the authority for your machine, and a few percent of variance either way is normal. If your measured consumption exceeds the full-load figure for your size, that's worth investigating as a service issue rather than accepting as normal.