Natural Gas vs Propane Generators: The Straight Comparison
Almost every home standby generator in the Nashua area runs on natural gas or liquid propane, and the choice shapes the install price, the runtime, and the upkeep for the life of the machine. Installers who sell one fuel arrangement tend to praise it and move on. This page compares the two honestly: how each fuel reaches the generator, how much a typical unit burns per hour, what that means in days of runtime, and how to decide when your street gives you no choice or a real one.
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How Each Fuel Reaches the Generator
Natural gas arrives through the utility's pipe network to the meter on your house, and the generator taps that supply through a dedicated gas line. There is no storage on your property and nothing to refill. If your street has gas service and your meter and line can carry the load, natural gas is infrastructure you already own. Propane arrives by truck and lives in a tank on your property, owned or leased from a propane supplier, and the generator draws from that tank through its own line and regulators. Propane makes a standby generator possible on any street, at the price of storage, deliveries, and tank math.
Consumption: The Numbers for a 22 kW Unit
The 22 kW class is the most common whole house size in this area, so it makes the cleanest example. Manufacturer figures for a current 22 kW class unit, and Generac's published guidance for the size, agree on the shape of the numbers:
| Fuel | At half load | At full load |
|---|---|---|
| Propane | About 2.45 gallons per hour (Generac's general guidance: roughly 2 to 3 gallons per hour) | About 3.71 gallons per hour (guidance: closer to 3 to 4 gallons per hour) |
| Natural gas | About 221 cubic feet per hour | About 311 cubic feet per hour |
Exact consumption varies by model, and older 22 kW units show somewhat different figures, so treat these as the right order of magnitude for planning and check the specification sheet for the exact model you are quoted. Loads in a real home cycle: the air conditioner starts and stops, the dryer finishes, the house coasts. Your average burn across a full day usually lands below a steady half load figure, which is why real world runtime tends to beat the conservative math below.
Runtime Math for Propane
Propane tanks are filled to about 80 percent of their rated size, to leave room for expansion. A 500 gallon tank therefore holds about 400 usable gallons. Divide by burn rate and you get continuous runtime for a 22 kW unit: at the full load figure of about 3.71 gallons per hour, roughly 108 hours, about four and a half days. At the half load figure of about 2.45 gallons per hour, roughly 163 hours, close to seven days. At the lighter cycling loads of a real house being careful, longer still. Now the important honesty: that math assumes the tank starts full and the outage starts the same hour. A tank at half when the storm hits halves the runtime. Propane ownership is a habit, like oil heat: watch the gauge, or fit a tank monitor, and treat a delivery before a forecast major storm the way you treat filling the oil tank in January.
Smaller tanks shrink the math fast, which is why a generator should rarely share a small heating tank without a sizing conversation. Your propane supplier and your installer should agree on the tank plan in writing: size, who supplies it, where it sits under the applicable placement rules, and whether the home's heating load shares it. Buried tanks are an option on many properties and remove the visible tank from the yard, at higher install cost.
The Natural Gas Side of the Ledger
Natural gas runtime is effectively unlimited for as long as the utility network holds pressure, which it does through the overwhelming majority of outages, since the gas network does not depend on the electric grid the way your furnace blower does. The constraints are different. First, capacity: the meter and the home's gas piping must feed the generator at full load at the same time as the furnace, water heater, range, and dryer. Generators are large gas appliances, and some homes need a meter upgrade or line work, which the installer verifies and the utility schedules. Second, output: some home standby models are rated a little lower on natural gas than on propane, so the size you buy is the size on your fuel, checked on the specification sheet. Third, dependence: in the rare event of a gas service interruption, a natural gas generator has no stored reserve. For most Nashua homes with gas on the street, those trade offs still land clearly in natural gas's favor on convenience.
Side by Side
| Natural gas | Propane | |
|---|---|---|
| Availability | Only where the street has gas service | Anywhere a tank can be placed |
| Runtime | Effectively unlimited while the network holds | Tank math: days, sized by tank and load |
| Refueling | None | Deliveries, gauge watching, storm season planning |
| Install work | Gas line run, possible meter upgrade | Line run, possibly a new or larger tank and trenching |
| Output note | Some models rate slightly lower on natural gas | Full rated output on most models |
| Site footprint | No storage on the property | A visible or buried tank, with placement rules |
| Other home uses | Shares the meter with heat, hot water, cooking | Often shares the tank with heat or other appliances |
How to Decide
If your home already heats with natural gas, the generator decision is usually made: connect to the same service, verify capacity, and enjoy the simplest runtime story in the market. If your street has gas but your home does not use it, the comparison is between the cost of bringing gas in, which may also serve future appliances, and the cost of a propane setup. If your home heats with oil or propane already, propane is the natural fit, and the project becomes a tank sizing exercise. If your home is all electric with no fuel on site, both fuels are new infrastructure, and the quote comparison should price both honestly, tank and all versus gas connection and all. In every case, decide fuel before final sizing, because output ratings, line sizing, and runtime all hang off the choice. One more cold weather note for propane homes: very cold weather reduces a tank's ability to vaporize fuel at high draw, another reason tank size is not the place to economize with a big generator in New Hampshire.
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Common Questions
Can a generator switch between natural gas and propane later?
Many home standby models are field convertible between the two fuels with the correct parts and settings, done by the installer. It is a real job, not a valve flip, and the output rating may change with the fuel. If you think a switch is in your future, name the model and ask about its conversion path at quote time.
Will a generator empty my propane tank and leave the house cold?
It can draw the shared tank down during a long outage, which is why the tank plan matters: adequate size, a gauge or monitor you actually check, and a supplier who knows a generator is on the tank. Homes where heat and generator share fuel should size for the outage case, not the average week.
Does natural gas ever fail in an outage?
Rarely, and usually for a local physical reason rather than the outage itself. The gas distribution network is pressure driven and independent of the electric grid for most homes. It is the most set and forget fuel story available, with the caveat that there is no on site reserve if service is interrupted.
What size propane tank does a generator need?
There is no single answer, because it depends on generator size, load, and whether the tank also feeds heat. The 500 gallon example on this page, with about 400 usable gallons and roughly four and a half to seven days of continuous runtime for a 22 kW unit, is the common planning case for whole house installs in this area. Smaller generators and essentials coverage can work with less. Get the tank plan in the written quote.
Which fuel is cheaper to run?
It depends on current local prices, which move. The honest way to compare is with the consumption table on this page and your own current price per gallon of propane and per unit of natural gas. Multiply your fuel's hourly figure at the load you expect by your price. Any page quoting a cost per hour without a dated local price is guessing, so this page does the consumption math and leaves the price to your latest bill.
Not Sure Which Fuel Fits Your Home?
Your street, your heating fuel, and your tank or meter situation decide it. One call sorts it out.