My Fifth-Wheel RV

A Guide to Living the RV Life
Skip Navigation Links

Propane Systems

T↑ T↓
Font size

Most RV-ers never give a second thought about their propane system until they have to refill a tank. Do you know how yours works? If you have multiple tanks, do you know which tank services which appliance(s)? Do you know how to check for leaks? Are tank monitors safe to use? Hmm.

Much of this discussion was taken from an web page, with their permission of course .

Propane is also known as LPG standing for Liquid Petroleum Gas, or simply LP. It is a by-product of natural gas processing and petroleum refining. For you chemistry nerds, its molecular formula is C3H8. Propane is not the only type of LPG; butane is another example.

LP gas has an additive called Ethyl Mercaptan that has a distinctive odor, something like rotten eggs. Since propane itself is odorless, LP manufacturers add this deliberately to alert users of a leak. Familiarize yourself with the smell so that you can instinctively recognize it.

Although propane is often referred to as "gas" it can also exist in a liquid state. In fact, when filling your LP tank, as pressure builds the gas starts to liquify. Pressurizing the propane into a liquid also causes it to drop down to about -40 F, which is why propane tanks feel cold to the touch. It’s also why condensation can form on them on hot, humid summer days. The propane fueled appliances in your rig are designed to use gas vapors only; they will not work on liquid propane. When you open the valve on a propane tank, the liquid propane actually "boils" into propane gas, which is then sent to the appliance through the hose/regulator.

Be sure not to overfill your tanks. In other words, only let an experienced person do the job!

Tank types

Most RVs have essentially the same type of system, although there are differences. Smaller rigs might only have one tank, while larger rigs can have two or four. Class A motorhomes will usually have a permanently mounted ASME [American Society of Mechanical Engineers] tank to hold liquid propane. These tanks are able to hold larger amounts of propane than those found on smaller rigs.

Other RVs likely have the familiar DOT (Department of Transportation) tanks like the ones you might use with your backyard BBQ grills. Capacities vary, but ASME tanks are usually a lot larger (and heavier) than portable DOT tanks.There are other differences as well.

ASME tanks
  • No Recertification period required.
  • Slightly thicker steel.
  • Heavier than a DOT tank of the same capacity.
  • Designed for stationary installation. Not designed to be moved when holding propane. Normally have to be driven to an LP filling facility.
  • Design & Standards governed by ASME.
DOT tanks
  • Recertification period requirements: 12 Years after manufacturing, then every y Years.
  • Designed for Portable Applications. Can be transported with propane if done so according to Code. Can be individually carried to an LP filling facility.
  • Design & Standards governed by DOT.
ASME propane tank
DOT propane tank

As a concrete example, ours fifth-wheel uses 4 DOT tanks - 18.9 gal [4.7 per tank, tank weighs 20 lb]

Here is a good discussion on the neverending discussion on whether to fill or exchange your DOT LP tanks.

Dual or quad tanks are found on most travel trailers and 5th wheel campers. These larger campers have larger appliances hence need more juice. Accessories such as an additional outdoor kitchen, an oven, and a larger heater require more propane to run than only a fridge and range. On travel trailers, the propane tanks are typically stored at the front of the trailer on the frame between the trailer and the coupler. For fifth-wheels the propane tanks may be stored in a single storage compartment, or they may be split to access tanks on either side of the camper.


DOT dual-stage regulators require 1/4 inch NPT fittings, but some setups come with 1/4 inch NPT to 1/4 inch Female Inverted Flare adapters. Whether or not your regulator already has these adapter fittings installed will tell you which type of pigtail hoses are needed on the trailer, those with 1/4 inch NPT fittings or those with 1/4 inch inverted flare fittings. Typically the fill valve, regulator, and optional tee fitting are located at the propane tank.

1. RV Pigtail Hose2. Regulator3. Hose Assembly4. Optional Propane Tee

Most smaller units have only a single 20 or 30 pound DOT tank. Larger units may have multiple tanks. In such cases the tanks will likely be installed in pairs with a changeover switch which determines which of two tanks propane will flow from. Dual tank systems usually have more appliances to service.

1. RV Pigtail Hose2. Regulator3. Hose Assembly4. Optional Propane Tee

Here is one example of a dual tank changeover system.


The jury seems to still be out on the effectiveness of LP tank gauges. Most people cannot tell how much fuel is left in a tank without some type of indicator. Experienced handlers can tall by weight, but probably not you are me. There are almost as many types of guages out there as Carter has pills. If you don't believe it, just look here. Some connect in-line with the hose. Some are magnetic thingies that stick onto the tank. Some are electronic. Some are cheapo and others can be expensive.

Personally, I haven't had good luck with in-line tank gauges. They often leak. The magnetic strips don't leak but using them effectively seems to be something of a black art. So I've gotten into the habit of just topping off whenever I'm close to a fill station. Maybe I'll try some more expensive gauges to see if they work better; if they do I would be happy. See here for a nice discussion of LP tank guages.

Finally, another thing to consider is whether you should leave your LP tanks on while travelling. Some say it's not a good idea since due to the chance of fire or explosion in the event of a traffic accident. If you're going to be on a relatively short trip then I think turning the tanks on and off shouldn't be much of a hassle. However, if you are going to drive a long way and have a fridge that can run on LP then leaving the tanks on is probably justified. Our fridge switches between 110v and LP, so letting it run on gas assures we don't have food spoilage when we get to our destination.


Propane tanks don't generally require maintenance other than periodically checking for leaks and making sure the connections are secure. The biggest causes of issues in the propane system are vibrations. If hoses aren't tight they can come loose on bumpy roads. This won't cause problems with fires or anything, but you could find yourself without propane supplied to your appliances. You can check for leaks by brushing or spraying soapy water onto connections. Don't forget to check the entire run, including the metal pipes which run under the rig to the appliances. The formation of bubbles is a sure indication of a leak. If the hoses are old be sure to check them too, not just the connections.

Should you discover anything seriously wrong with your propane system, like a leak in the lines under the chassis, immediately turn off the tanks and contact a qualified LP technician to effect repairs. Endangering yourself, your family or your rig isn't worth saving a few bucks!

This website developed by Black Vanda Productions LLC   Copyright © 2019. All Rights Reserved.