How To Estimate How Much Propane You Need in Your RV

A house relies on natural gas piped in from a local gas company to operate some appliances. RVs on the other hand, are engineered to deliver the same heating and cooking conveniences of home, but in a mobile package. But how?

For most RV models, many major amenities are powered by the propane system, like refrigeration, hot water, and HVAC. You can start to see how running out of propane could really interrupt your RVing plans. Knowing how RV propane systems work will help you estimate the amount of propane you’ll need on a trip so you don’t run out at the wrong time. By the end of this article, you’ll know how to troubleshoot why the propane is not flowing and solve issues on the fly.

Why Do RVs Use Propane?

Let’s take a moment to remember our grade school science:

Gases change state between liquid and vapor in response to changes in pressure and temperature.

At higher pressure, the fuel molecules are compressed into liquid form (also dropping in temperature). At lower pressure the liquified molecules expand, vaporizing into gaseous form (also warming in temperature).

To simplify this concept, imagine how water (liquid) boils into water vapor (gas) as its temperature rises. The hot water molecules expand or spread out pushing against their surrounding pressure. In other words, boiling point is the temperature at which a liquid’s vapor pressure becomes equal to the pressure of the surrounding air. That’s why elevation and environmental conditions affect your RV’s propane system performance. As the outside temperatures cool, the propane contained inside the tank must work harder to overcome the liquifying pressure.

Propane, Butane, Natural Gas

So, why propane? Propane has a lower boiling point (-44°F) than butane (31°F), meaning propane vaporizes more easily than butane. For RVers, this allows propane to be used year-round, even when the weather drops below freezing.

Most homes are powered by natural gas, which vaporizes at an even lower temperature than propane (-259°F). This particular chemical property also makes natural gas unfeasible for portable applications. For commercial shipping, liquified natural gas must be stored in double-walled cryogenic containers. Of these combustible gases, propane is the most practical for RVs.

When investigating propane alternatives, performance factors outside of transportability and vaporization are weighed, like:

• heat production (temperature intensity)
• cooking capacity (energy potential by volume)
• combustion efficiency (range of flammability)
• footprint considerations (lightweight and repair parts support)
• eco-friendly clean-burning fuel (greenhouse gas emissions per productivity unit)
• budget constraints

A Basic Understanding of Your RV Propane System

Appliances burn gas, not liquid. However, transporting gas can be unsafe, so propane travels in liquid form for safety and convenience.

Pressurization transforms the propane between liquid and gas states. Propane flows from the tank, through the propane lines made up of hoses, to the appliance. Located along the propane lines are a combination of pressure regulators, which control and adjust the gas pressure to deliver a consistent flow at usable pressure for each connected appliance. Excess flow valves located inside the propane tank valve outlet, propane hose connection fittings, and pressure regulators detect potential propane leaks in the system.

RV Propane Tanks

Propane is a type of liquified petroleum gas (LPG). As an LPG container, propane tanks are subjected to federal regulation and periodic recertification. The intervals are driven by its original manufacture date on the tank label as well as the most recently applied requalification method.

There are two types of RV propane tanks:

• Permanently mounted RV propane tanks, used in motorhomes, are ASME-certified (American Society of Mechanical Engineers). ASME tanks vary in size.
• Portable RV propane tanks (aka Cylinders)—typically used with travel trailers, fifth wheels, truck campers, and smaller motorhome conversions—are DOT-certified (Department of Transportation) versions of the ones designed for backyard BBQs. The most common portable propane tank sizes are 5-gal and 7-gal (which are interchangeably referred to as 20 and 30 pound tanks, respectively). Gallons describe the liquid volume while pounds describe the mass of its gaseous form.

Propane Replacement and the 80% Fill Rule

Both types of RV propane tanks are refillable. Plus, you can conveniently exchange an empty portable propane tank for a full one.

For safety, propane tanks can only be filled to 80% to allow for gas expansion. To comply with this rule, RV propane tanks manufactured after 1998 are designed with an internal overfill valve preventing more than 80% liquid propane. You can verify whether your propane tank is equipped with an overfill prevention device (OPD) by looking at its knob (tank valve). Across all manufacturers, the knob will be triangular-shaped and stamped “OPD” in contrast with the older non-compliant pinwheel or round-shaped knobs.

Because of RV industry vernacular, some RVers become confused about whether the marketed tank size describes the amount of propane held when filled to 80% capacity or not. The safe bet is to check your specific propane tank for stamped markings and labeling details. While this piece of information is required, uniform display of this data has not yet been established across all propane manufacturers.

RV Propane Regulator

Regulators are devices that reduce the high pressure coming from the propane tank to a pressure that is usable by your RV appliances. RV propane systems are required to use a two-stage regulator to control the system pressure. The first stage reduces the pressure to a consistent flow while the second stage further lowers the pressure to an appliance operating pressure. Additional regulators can also be designed into the propane line—either at the gas entry point or internal to the appliance—to closely control the propane pressure as it enters that appliance.

RV Propane Appliances

Propane-burning appliances are rated in BTUs per hour, a measurement of thermal energy. BTU input is the amount of energy an appliance requires to operate, while BTU output is the amount of energy delivered as heating or cooling. If the appliance operates at 100% efficiency, the input BTU rating would be equal to its output BTU rating.

Look at the label or technical manual to find the model-specific BTU ratings of your RV appliance. If the BTU rating is missing, you can calculate it using simple math. Take note of the watts or the volts and amps provided and plug into the Easy Math formula below.

Excess Flow Valve

Excess flow valves close automatically when it detects propane gas leaving the tank faster than the valve’s flow capacity rating. A pressure leak in the propane line would cause elevated flow rate, triggering an excess flow valve. It’s important to remember that the excess flow valve may not detect all pressure leaks in the propane line due to the propane system configuration.

RV Propane Leak Symptoms and Safety Detection

Propane gas is heavier than air. If the RV propane system is leaking, then the gas will settle to the ground posing an inhalation hazard. Inhaling propane gas displaces the oxygen in your lungs and can cause asphyxiation. Symptoms of propane inhalation include rapid breathing, rapid heart rate, clumsiness, nausea and vomiting, fatigue, collapse, and convulsions. Coma and death can occur from asphyxiation, even though propane is a non-toxic substance.

In its natural state, propane is actually odorless. So, a pungent rotten egg smell is mixed with the propane for leak detection. For these reasons, LP detectors are required with RVs (since 1996).

If you smell or hear either of those things, shut off the propane tank immediately and extinguish any open flames. Then, call a certified RV service professional to diagnose and repair the propane system. Good Sam members can also call the Elite Service Tech Advisor support line for a real-time, step-by-step troubleshooting walkthrough for your specific RV model.

Do I Have a Propane Leak?

Oftentimes, this is an RVer’s first thought when the propane doesn’t last as long as expected.

If your LP detector isn’t sounding the alarm and you don’t smell rotten eggs, then the system is probably not leaking propane. Instead, it’s likely a performance issue causing a propane flow restriction or miscalculated propane consumption.

Basic Troubleshooting for Your RV’s Propane System

First, double-check your propane tank gauge is not sitting on empty and the tank is turned on. If equipped with an RV propane automatic changeover for dual tank hook-up, check whether the component malfunctioned. If the RV propane is not flowing to your appliances listed in the Venn Diagram above, follow the flowchart below:

Before attempting to remove and replace damaged parts within your RV propane system, determine whether you have the skills, proper tools, and safety gear because of potential injury or explosion.

Environmental Factors

Take note of the ambient temperature, elevation, and propane level. These conditions affect your RV’s propane system performance. In colder weather and lower altitudes, liquifying pressure increases. Also, if the propane tank is nearing empty in cold weather, the gases won’t expand enough to be extracted from the tank.

Optimize internal tank pressure by controlling temperature and propane level. To ensure the proper pressure inside the tank, keep it warm with a propane blanket. For safety reasons, do not store the propane tank in a heated living space. You can also replenish your propane more frequently to maintain an optimal fluid level. For every season, optimizing your RV for propane conservation saves money in the long term.

Excess Flow Valve

Check whether the excess flow valve in the propane hose is engaged. When connecting your propane tank, the propane hose fitting may have been improperly threaded onto the tank fitting. That prevents the spring mechanism of the excess flow valve from seating correctly. Disconnect the hose and reattach more carefully to avoid cross-threading.

Pressure Regulator

Inspect the regulator for water damage, corrosion, or neglect. If the pressure regulator looks fine, check around the burners (stove, furnace, water heater) for symptoms of an RV propane regulator problem—yellow or orange flames, soot build-up, roaring noise or popping sounds. Caused by restricted propane flow, these symptoms indicate the excess flow valve inside the pressure regulator may have been triggered. If you do not see any of these symptoms, then the propane tank valve may have been opened too quickly when turning on your propane.

Make sure your appliances are shut off. Then, close your tank valve so the pressure regulator resets itself. Wait 5-10 minutes before slowly opening the tank valve. This re-pressurizes the RV propane system.

Propane Hoses and In-line Valves

If the restricted propane flow symptoms continue after resetting the pressure regulator, then one or more propane lines may have a kink or an in-line valve may be closed. This depends on the type and placement of hoses and connectors used for your RV propane system configuration.

Before tracing the propane line, do some Easy Math to check whether your propane consumption exceeds your RV’s propane storage capacity.

Easy Math: How Long Will My Propane Last?

Surprisingly, a propane leak is not the primary culprit for running out of propane. Usually, RVers simply underestimate propane consumption by forgetting to account for all propane-burning appliances or miscalculating propane usage hours.

Knowing your baseline propane usage rate will help you plan accordingly so you avoid running out of propane. Use the following formulas to determine how much propane your RV system supplies. Compare that with your estimated propane consumption for the trip. This should tell you whether your propane demand exceeds the available supply.

As explained previously, propane is designated by gallons, pounds, and BTUs.

• Its liquid/liquified form is measured in gallons.
• Its vapor/gaseous form is measured in pounds.
• Its thermal production/reduction is measured in BTUs.

You’ll also need to know key propane conversion rates:

• 4.2 pounds of gas = 1 gallon
• 21,548 BTUs = 1 pound of gas

To use the formulas for determining propane consumption, refer to the numeric ratings of RV propane system components (propane tanks, stove, furnace, coffee maker, water heater, etc.) and plug those numbers into the following equations:

• Tank BTUs = (tank pounds x .80) x 21,548
  This converts the amount of propane into BTUs.
• Maximum BTUs = Add up the Tank BTUs for all propane tanks
  This calculates the amount of BTUs your propane system is equipped with for operation.
• BTUs Per Hour = The model-specific amount of BTU gas input burned per hour
  If the appliance BTU rating is missing, use volts, amps, and watts to calculate:
  • BTUs Per Hour = Watts ÷ 3.413
  • BTUs Per Hour = (Volts x Amps) ÷ 3.413
• Total BTUs = Add up the BTUs Per Hour for each appliance
  This calculates total BTUs burned for 1 continuous hour of operation.
• Baseline Consumption = Maximum BTUs — Total BTUs
  This calculates total propane consumption for each hour of continuous operation—assuming optimal efficiency.
• Available Usage Hours = Maximum BTUs ÷ Baseline Consumption
  This estimates how long the propane-burning appliances can operate.
• Planned Usage Hours = Number of hours
  This is the estimated amount of time you want to operate propane-burning appliances.
• Remaining Propane Available = Planned Usage Hours — Available Usage Hours
  This estimates how much propane left to operate propane-burning appliances.

If your Available Usage Hours exceed your Planned Usage Hours, you’ll need to carry more propane tanks or schedule a refill.

Propane Usage Planning

How many hours would you and your family generally run each RV appliance on a given day?

For a more accurate baseline consumption picture, estimate planned usage based around your RVing lifestyle. Make a detailed breakdown of Total BTUs by taking BTUs Per Hour multiplied by Planned Usage Hours specifically for each appliance. If you’re a highly structured RVer or data-driven consumer:

• Rank your appliances by priority. This way, you’re prepared if you need to cut propane consumption.
• Chart your usage estimate around the anticipated activities for each day of a specific trip.
• During your trip, adjust future planned usage hours based on actual usage observations.

If you want complete confidence for how much propane you’re working with, add an propane level monitoring device (on-tank or remote display) or an in-line propane gauge with built-in propane leak detector to let you know when your propane tank is running low.