Propane-Powered Generators: Are They the Best Choice?

July 17, 2020

Recently I was asked the following question by someone who wants to install a 5000-watt generator to run their home in case of a power failure:

What is the best choice for fuel, propane, gasoline or diesel?

This reader is leaning towards getting a propane-powered generator. The choices are confusing, and a guide like this one can help the newcomer to the world of generators make the best choice.

I have been doing some research on the subject and here are some of the advantages and disadvantages of all three fuels for generators: gasoline, diesel, and propane.

Propane produces 92,000 BTUs per gallon, gasoline is capable of producing 114,000 BTUs per gallon, and diesel is capable of producing 129,500 BTUs per gallon. This means that it will take more propane per hour that either gasoline or diesel to run a generator.

Explanation of Terms

First, it would be helpful to know a few terms that will come up consistently in reference to calculating how much propane a generator uses.

Terms:

  • Pound – measurement of how much propane a generator uses.

  • Gallon – measurement of how much propane is dispensed from a tank.

  • Watts – a measure of how much power an appliance uses.

  • Kilowatt (kW) – how much power a generator uses. There are 1000 watts in a kilowatt.

  • BTU – British Thermal Units, a unit of energy for how much heat an appliance produces. Propane has a fuel value of 92,000 BTU per gallon.

  • Cylinder – a portable tank used to store propane.

  • Tank – how stationary propane tanks are measured. Most propane tanks hold 500 to 1,000 gallons.

General Facts

Propane is a gas that is stored in liquid form. When the tank reaches a certain pressure, the propane turns to gas and dispenses from the tank. The pressure in the tank is measured in pounds per square inch (psi).

Most generators will use between 25-75% of their capacity when running on propane to make the fuel supply last longer.

You can buy propane in portable cylinders that range in size from 20 to 100 gallons. You can also have a stationary tank installed at your home or business. A 20-gallon tank is the equivalent of a 500-pound cylinder.

The cylinders are available at most home improvement stores, and you can order the larger tanks through a propane company.

Propane, Gas, and Natural Gas

When choosing a generator, you have the option of running it on either propane, gas, or natural gas.

While gasoline generators are less expensive upfront, they can be more expensive to operate in the long run, as propane is about half the price of gasoline.

Gas generators are also less efficient than propane generators, so you will use more fuel running a gas generator.

Propane-powered generators are also more eco-friendly, as they produce fewer emissions than gas generators.

Natural gas lines can be damaged during a hurricane or severe storm, but propane tanks can withstand high winds.

Furthermore, natural gas lines are not available in all areas, but propane tanks are.

Liquid propane doesn’t go bad and has a long shelf life, so you can store it for long periods of time without having to worry.

A generator powered by propane has enough power to run your entire home. If hooked up to a 500-gallon tank, a typical generator can power your home continuously for a week.

Calculations: How Much Propane Does A Generator Use

Now that you understand the basics, we can calculate how much fuel a generator will use.

On average, a generator uses 2 to 3 pounds of propane per hour. However, this amount can vary depending on the size of the generator and how high the wattage is.

  • It requires 2 horsepower to produce 1000 watts of energy per hour under load

  • Under load each horsepower consumes 10000 BTU per hour

  • Propane contains 92,000 BTU per gallon

  • Propane weights 4.2 pounds per gallon

Using these factors how long can a 5000-watt generator run on a 500 gallon propane tank at 50 capacity.

  • 10 horse power at 50% would use 5 HP to generate 2500 watts of electricity

  • 5HP X 10,000 BTU would consume 50,000 BTU per hour

  • 500 gallons X 92,000 = 46,000,000 BTU of energy in a full 500 gallon tank

  • 46,000,000 BTU divided by 50,000 BTU = 920

  • A 500-gallon tank that is full would run a 500-watt generator at ½ capacity for 920 hours.

After comparing the various fuels, I would probably go with propane for a large generator in a fixed setting. I would want a minimum of a 1000 gallon tank. For small generators I would go with a tri-fuel generator. Tri-fuel generators burn propane, gasoline and natural gas.

If you choose to purchase a large generator you need to weight the cost versus the benefits. Is running a generator worth the cost? Another consideration is how much fuel you are able to store. Propane tanks store indefinitely, which is another reason the propane generator is a good choice.

General formula:

Pounds of propane used = propane consumption per hour x working hours + hours in case of emergency

So, if you have a generator that consumes .75 pounds of propane per hour and you plan to use it for six hours during a storm, the total amount of propane used would be:

.75 pounds per hour x six hours = four and a half pounds of propane used

Propane consumption per hour formula:

To calculate the propane consumption per hour, it’s easiest to break it down into steps.

The first step is to calculate horsepower.

Horsepower = (watts / 1000) x 2

The watts here refer to the power the generator is using, which depends on the appliances you want to power.

Some average appliance watts:

  • Refrigerator with freezer: 700 watts

  • Television: 200 watts

  • Laptop: 50 watts

  • Light bulb: 60 watts

  • Washing machine: 1200 watts

  • Sump pump: 1000 watts

Next, we calculate the BTU.

BTU per hour = Horsepower x 10,000

Finally, you calculate the gallons of propane.

Gallons of propane = BTU/92000

Example:

Let’s say you want to power a refrigerator that uses 700 watts for 8 hours, here’s how we would calculate that:

Horsepower = (700/1000) x 2

Horsepower = 1.4

BTU = 1.4 x 10,000

BTU = 14,000

Gallons of propane = 14,000/92,000

Gallons of propane = .15 (per hour)

Now all of this information can be plugged into the original formula. We would say you should add three or more hours as your emergency hours.

Pounds of propane used = .15 x (8+3)

Pounds of propane used = 1.65

So it takes 1.65 pounds of propane to power a generator to power a refrigerator for 8 hours.

Please note that the efficiency of your generator may change based on the model. Most portable generators are made to connect to a 20-pound cylinder, while larger stationary generators use a 30 or 100-gallon tank.

FAQs

How long will a generator run on a 20-gallon propane tank?

A 20-gallon propane tank can run a generator for up to six hours.

How long will a generator run on a 100-gallon propane tank?

A 100-gallon propane tank can run a generator for up to 25 hours.

How much does it cost to fill a 20-gallon propane tank?

It costs about $30 to fill a 20-gallon propane tank.

How much does it cost to fill a 100-gallon propane tank?

It costs about $120 to fill a 100-gallon propane tank.

How much propane does a generator use to power my house?

Whole house generator use is difficult to answer as it depends on how many appliances you want to run simultaneously and how big your house is.

A good rule of thumb is to calculate how many watts you need and use the formula above.

Is propane the most eco-friendly?

Propane is a cleaner burning fuel than gas but natural gas is the most clean burning fuel. However, remember that natural gas is not found everywhere.

Conclusion

Now you know how to figure out how much propane a generator requires based on the appliances you want to power. You can easily know how many gallons of propane to stock up on to be prepared for any power outage.

Feel free to leave any questions in the comments below!

No matter what kind of generator you decide to purchase they all deliver the same benefits when the power goes out.

Updated March 2022

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