Propane vs. Diesel Generator


How long can any business survive without power? Keeping the lights, heaters, appliances, and machinery running requires a continuous backup power source during an outage. Most businesses can’t wait more than a few minutes before they start to lose production and money. Homes also need a reliable backup source of electricity for emergencies and prolonged outages.

Electrical generators come in many wattages and amperage output options for construction sites, industrial-sized buildings, and smaller versions for homes and RVs. Permanent or standby generators sit on a sheltered concrete pad near the building they will supply power. Portable generators are small enough to fit in the back of a pickup truck to go wherever needed.

Once you determine your electrical needs and generator size, the next question is, which is better, propane or diesel?

Choosing the Right Diesel or Propane Powered Generator

The type of fuel you’ll use to power the generator is a critical factor when selecting a new backup power system. Most businesses use diesel or natural gas to power their generators. Homeowners can use propane, natural gas, or gasoline. It depends on what fuel is most available for your location. If you already have LP gas piped to the building, or you have a large diesel tank on-site to fuel the fleet, it makes sense to tap these existing supply resources. 

Here’s a look at some top considerations when determining whether diesel or gas generators best suit your needs.

Diesel Gas
Fuel Efficiency Diesel will have a higher efficiency rating because it packs more BTUs per unit when compared to propane. Propane may be less expensive but doesn’t produce as much energy.
Availability and Ease of Access Available in most areas. Requires external storage tanks. Available in most areas. Requires external storage tanks.
Generator Maintenance Diesel engines last longer because they have fewer critical parts like spark plugs and wires. Also, diesel helps lubricate the moving parts. A diesel generator requires maintenance every 500 hours. With propane, a carburetor is unnecessary since the fuel is already gas. That’s one critical component that won’t fail. A propane generator requires maintenance every 100 hours.
Generator Lifespan With regular maintenance, a low-usage diesel generator can last for decades. With regular maintenance, a low-usage propane generator can last for decades.
Safety Least likely to cause a fire if there is a leak. Exhaust fumes are hazardous unless vented outside. It can cause an explosion if there is a leak. Exhaust fumes are hazardous unless vented outside.
Environmental Concerns Adding DEF to diesel helps reduce emissions such as carbon monoxide, sulfur dioxide, and others. Learn more about this required additive on our DEF FAQ page. Propane burns much cleaner than diesel. Since it’s gas, it won’t pollute groundwater if there is a large spill.

Let’s examine the features of diesel vs. propane generators.

Propane Generators 

Propane or LP gas generators are becoming more common and can be a better choice than gasoline. Here’s why:

  • Propane stores indefinitely
  • Easy to get in an emergency
  • Clean burning, less pollution
  • Generators do not need a carburetor

There are a couple of drawbacks to propane. First, you may need to drive long distances to refill portable tanks or schedule a delivery far in advance with larger tanks. 

Propane does not deliver the same energy as diesel. Propane provides 26 Megajoules per liter, while diesel fuel creates almost 35 MJ/L. Propane burns much cleaner, but the engine usually has a shorter life cycle.

Is It Cheaper to Run a Generator on Propane? 

There are two factors when weighing the difference between fuel types to run a generator, fuel cost, and energy output.

For example, if you buy 1 gallon of “Fuel A” at half the price of a gallon of “Fuel B,” is that the best choice? Not necessarily. If Fuel A produces only a fifth of the energy of the same volume as Fuel B, Fuel A will be more expensive to run.

Let’s look at some real numbers. One gallon of diesel can produce about 33kW per hour of energy. That same gallon of propane will produce just 27kWh of energy. If a gallon of propane costs $2.40, using the formula, $2.40/27kWh = $0.088 per kWh. Using the same formula and price for diesel ($2.40), it produces electricity for $0.073 per kWh. 

We did not factor that a generator loses 80% of the energy. In other words, they are only 20% efficient. Adding the inefficiency to our equation means you pay 5 times more for your electricity. In this example, propane costs around $0.044 per kWh and $0.036 per kWh for diesel, which means diesel is 20% cheaper to run than propane.

You’ll need to use current prices for your area to get an accurate picture. Check with your fuel company or a generator supplier for precise analysis.

How Long Will a 500-gallon Propane Tank Run a Generator? 

To answer how long a 500-gallon tank will last accurately, you’ll need to know the size of the generator or kilowatt output and its load.

A 20kw propane generator, on average, will use at least 2 to 3 gallons per hour. A 500-gallon tank filled to its maximum safe level of 80% holds 400 gallons. That means the tank should last between 133 to 200 hours.

Diesel Generator 

Diesel backup generators are a popular choice in urban areas, or wherever diesel is readily available. Whether portable or large standby generators, diesel offers a few advantages. 

  • Inexpensive operating cost
  • Good fuel availability
  • Fuel-efficient
  • Least likely to cause a fire
  • Generators tend to last longer 

There are a few disadvantages as well. Diesel generators produce more emissions than propane generators, which can be a concern in areas with strict pollution laws or near schools and hospitals. Diesel engines must add DEF to control emissions.

Diesel Exhaust Fluid (DEF) is an additive that reduces the toxic gasses like carbon monoxide emitted by diesel engines. It’s a requirement for generators, and you can expect DEF consumption to be about 10% of diesel consumption. To get up to speed on this additive, checkout DEF FAQ.

For large standby generators, that means having a tote-sized container on hand along with the fuel storage tank. As DEF is 90% de-ionized water, it is susceptible to freezing. Not to worry, we have the solution in our guide, DEF tote freeze protection

Diesel fuel needs the right temperature and an additional ingredient to work at peak efficiency. Diesel engines can be hard to start in cold weather, and the fuel can turn jelly. To avoid issues in freezing weather, you may need to invest in a tank heater.

Dual-Fuel Generators

As the name implies, a single generator can quickly convert from gasoline to LP or propane as the fuel source. A dual-fuel generator is an ideal backup in areas that experience frequent outages due to weather. One 5500-watt model claims it can run eight hours on four gallons of gas or longer with propane.

Most propane portable generators have dual-fuel capacity.

Which is Better, a Propane or Diesel Generator?

As we’ve seen, both fuels have their advantages and disadvantages. 

Although a home or business may already have propane connected, it primarily provides heat energy via a furnace. Modern propane furnaces are highly efficient, with little wasted energy. However, a generator combustion engine is inefficient. The best ones convert only 35% of the fuel’s heat into mechanical energy. Since diesel fuel contains more energy than propane or natural gas, it’s a better choice for powering generators.

Diesel generators last longer and require less maintenance. Why? Diesel engines are simpler with fewer moving parts. They don’t have spark plugs, a carburetor, or an ignition system, and diesel fuel helps lubricate and cool fuel injectors. Unlike propane engines that require oil changes every 100 hours, a diesel engine won’t need an oil change for 500 hours. 

Diesel generators last well over 15 to 20 thousand hours and are quieter because they run at about 1,800 rpm, nearly half the speed of a propane generator. If we compare fuel consumption, a typical home generator consumes 4 gallons of propane an hour, and a diesel model uses only a 1/2-gallon.

Diesel is the best choice for long-term service if it’s practical for your location.

Is It Cheaper to Run a Generator on Gas or Propane? 

We need to mention propane vs. gas generators as gasoline fuels many home and RV generators. Propane has advantages over gasoline because it:

  • Lasts longer
  • Has a longer shelf life
  • Won’t gum up the generator’s carburetor

Although propane contains only about 10% less BTUs than the same volume of gasoline, it’s cheaper to run a generator with it.

Power Generation Solutions

Power outages are happening more often, with greater severity, and in more regions than ever. A backup generator that can run for days or weeks without fail is no longer a luxury.  

Natural gas and propane should be fine in a metropolitan area with only a few hours a year of outages. These types of generators don’t have the longevity of diesel systems. Consider diesel if you depend on uninterrupted electrical power, such as a manufacturing facility or a hospital. 

Don’t forget about cold weather applications. Building the infrastructure and maintaining diesel, DEF, or propane tanks during the winter takes extra precautions. No matter your fuel, visit our Construction Solutions page for tips on cold-weather locations. 


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