Propane Fuel Basics

Also known as liquefied petroleum gas (LPG) or propane autogas, propane is a clean-burning alternative fuel that's been used for decades to power light-, medium-, and heavy-duty propane vehicles.

Propane is a three-carbon alkane gas (C3H8). It is stored under pressure inside a tank as a colorless, odorless liquid. As pressure is released, the liquid propane vaporizes and turns into gas that is used in combustion. An odorant, ethyl mercaptan, is added for leak detection. (See fuel properties.)

Propane has a high octane rating, making it an excellent choice for spark-ignited internal combustion engines. If spilled or released from a vehicle, it presents no threat to soil, surface water, or groundwater. Propane is produced as a byproduct of natural gas processing and crude oil refining. It accounts for about 2% of the energy used in the United States. Of that, less than 3% is used for transportation. Its main uses include home and water heating, cooking and refrigerating food, clothes drying, and powering farm and industrial equipment. The chemical industry also uses propane as a raw material for making plastics and other compounds.

Propane as an Alternative Fuel

Interest in propane as an alternative transportation fuel stems from its domestic availability, high-energy density, clean-burning qualities, and relatively low cost. It is the world's third most common transportation fuel, behind gasoline and diesel, and is considered an alternative fuel under the Energy Policy Act of 1992.

Propane used in vehicles is specified as HD-5 propane and is a mixture of propane with smaller amounts of other gases. According to the Gas Processors Association's HD-5 specification for propane, it must consist of at least 90% propane, no more than 5% propylene, and 5% other gases, primarily butane and butylene. (See fuel properties.)

For vehicle fueling, the quick-release "Type K15" dispenser connector is required to be installed on all new vehicles beginning January 1, 2020, per National Fire Protection Association Code 58. This connector allows for one-handed fueling and does not require the use of personal protective equipment such as gloves and face shield (which are required for the older style connector).

Propane is stored onboard a vehicle in a tank pressurized to about 150 pounds per square inch—about twice the pressure of an inflated truck tire. Under this pressure, propane becomes a liquid with an energy density 270 times greater than its gaseous form. Propane has a higher octane rating than gasoline, so it can be used with higher engine compression ratios and is more resistant to engine knocking. However, it has a lower British thermal unit rating than gasoline, so it takes more fuel by volume to drive the same distance.

To find the fuel, see propane fueling station locations. For retail fuel prices, see the Alternative Fuel Price Report.

Your furnace is a controlled fire burning in your home.

Before you let that scare you, let’s talk about the amazing safety features your furnace has to keep you safe while it keeps you warm!

There are five safety features some furnaces have that are important to learn about: a Flame Rollout Sensor, a Flame Proving Sensor, a High Temperature Limit Control, a Flue Exhaust Pressure Sensor, and a Fan Limit Sensor.

Flame Rollout Sensor

Do you know the three ingredients of fire?

Your furnace is a controlled fire burning in your home. Fortunately, there are safety features that keep things safe for your family.

Oxygen, heat, and fuel! In order to make your home warm and cozy, your furnace starts a fire in a fire box by using these three ingredients. The gas valve releases raw gas to serve as the fuel. This gas in the fire box comes in contact with the heat source. Depending on your unit, this would either be a pilot light, a hot surface ignitor, or a spark ignitor. When the gas and heat source meet, they use any available oxygen while in the fire box to ignite a fire. This fire is supposed to stay in the fire box, where it’s safely contained and can provide your furnace with warmth. If there’s not enough oxygen for combustion, however, the flame will “roll” out of the furnace in search of the oxygen it needs! Your Flame Rollout Sensor senses when the flame leaves the furnace, and it tells your heating system to shut off the furnace.

What happens when the Flame Rollout Sensor isn’t working right? If this sensor malfunctions, the flame might catch the floor joists, nearby walls, or attic trusses on fire!

Recommended: “The Silent Killer Hiding in Your Home”

Flame Proving Sensor

Our safety experts take the time to check each safety feature during your maintenance to make sure they’re working right to protect your family!

Remember when we talked about how the gas valve releases raw gas into the fire box? Your furnace may also be equipped with a Flame Proving Sensor, which detects when there’s a flame in the fire box. If it detects a flame, it allows the gas valve to stay open and continue releasing gas to keep the fire alive. When it doesn’t detect a flame, it shuts off the gas valve.

What happens when your Flame Proving Sensor isn’t working right? If this sensor malfunctions, it continues to allow raw gas into the combustion chamber without a flame actively using it up. If this happens, even a small spark on that much gas can cause a huge explosion.

High Temperature Limit Control

Some of the safety features in your furnace will shut your furnace off when they detect a problem, and some of them require a professional to reset them. If your furnace won’t turn on, give us a call! We’ll get to the bottom of things!

In order to heat your home, your furnace has got to get really hot. Of course, there’s a limit to how hot your furnace should get though! Your furnace comes equipped with a High Temperature Limit Control, which has a set limit of how high the temperature of the furnace is allowed to get. If your furnace exceeds this limit, the High Temperature Limit Control shuts off your system.

What happens when the High Temperature Limit Control isn’t working right?

If this control malfunctions, it could burn out your heating system. This can cause one of two problems: either there will be too much heat and you’ll end up with damage to your fire box, or you won’t have enough heat in your home because your unit keeps shutting off. When this happens, you’ll need to call a professional to fix your unit.

Recommended: “Why Your Furnace Is Blowing Cold Air”

Flue Exhaust Pressure Sensor

In order for your furnace to safely ignite, it has to do a couple things. It’s gotta provide the proper amount of combustion air to the gas and flame, and it has to make sure there are no blockages in this process. Basically, it makes sure the inducer motor (it’s like a fan) is pulling smoke through the heat exchanger and pushing it through the flue so it can escape your home. If there are no blockages, the sensor will let your unit know it’s ok to turn on the gas and ignitor. If there’s a blockage, your furnace won’t turn on.

Did you know? Your inducer motor has a short lifespan. They usually only last between 8-10 years, so it’s important to get it checked every year!

What happens if the Flue Exhaust Pressure Sensor isn’t working right? If this sensor malfunctions, your unit won’t be able to turn on and you’ll need to call out a professional to fix it.

Fan Limit Sensor

In order to bring heat into your home, your furnace uses a type of fan called a blower to blow air over the heat exchanger. If the blower stops working or isn’t providing enough airflow over the heat exchanger, your Fan Limit Sensor will shut off the furnace.

What happens if the Fan Limit Sensor isn’t working right? If this sensor malfunctions, your heat exchanger will continue to get really hot and won’t have the air from a fan to push heat away from it. This means your heat exchanger would get red hot, which could allow cracks and splits in the steel. A crack in your heat exchanger is dangerous because it can allow carbon monoxide into your home!

Related: “Do You Have a Crack in Your Heat Exchanger?”

Staying Safe and Warm

When things start getting cold in the Carolinas, a furnace is a fantastic way to keep your family warm and cozy! We know all of this can make them sound a little scary, but don’t worry! These sensors and controls are meant to keep your family safe. The best thing you can do for your furnace is schedule a Safety Check to make sure all your furnace’s safety features are in great shape to last the winter ahead! Each of our technicians is a certified safety expert, and when you schedule service, your tech will check out everything super thoroughly. We don’t take shortcuts, especially when it comes to your family’s safety. You deserve to stay safe and warm this winter!