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Glossary of RV Terms


120AC 12DC

The power sources on which RV refrigerators operate. 120 AC means 120-volt alternating current (same as in houses); 12 DC means 12-volt direct current (same as in automobiles). Some RV appliances can operate on either electricity source and/or propane gas.

Anode Rod

When used in a water heater, an anode rod attracts corrosion causing products in the water. These products attack the anode rod instead of the metal tank itself. The anode rod should be inspected yearly and changed when it is reduced to about 1/4 of its original size. The rods are used in steel water heater tanks: an aluminum tank has an inner layer of anode metal to accomplish the same thing. Anode rods should not be installed in an aluminum tank.

Axle Ratio

The ratio between the pinion and ring gears in the differential that multiply the torque provided by the engine. It is the number of drive line revolutions required to turn the axle one time. For example, with a 4.10:1 axle the drive line turns 4.1 times for each full axle revolution. The higher the number, the more torque and thus more towing power. However, higher axle ratio also means less speed.

Black Water

Water from a toilet system held in an onboard holding tank until a means of disposal is available.


Camping without hookups. The term is also used among campers who like to enjoy nature at its fullest, regardless of the terrain, and avoid commercial campground fees.

Brake Controller

A device mounted under the dash of a towing vehicle to control the braking system of the trailer. The brake controller senses the amount of braking force of the tow vehicle and applies a proportional force to the trailer braking system.

Breakaway Switch

A safety device that activates the trailer brakes in the event a trailer becomes accidentally disconnected from its hitch while traveling.

BTU (British Thermal Unit)

A measurement of heat required to raise the temperature of one pound of water one degree Fahrenheit. RV air-conditioners and furnaces are BTU-rated.

Castor (Wheel alignment)

A steering wheel's tendency to return to dead center after the driver turns a corner.

Class A Motorhome

An RV with the living accommodations built on or as an integral part of a self-propelled motor vehicle. Models range from 24 to 40 feet long.

Class B Motorhome

Also known as a camping van conversion. These RVs are built within the dimensions of a van, but with a raised roof to provide additional headroom. Basic living accommodations inside are ideal for short vacations or weekend trips. Models usually range from 16 to 21 feet.

Class C Motorhome

An RV with the living accommodations built on a cutaway van chassis. A full-size bed in the "cabover" section allows for ample seating, galley and bathroom facilities in the coach. Also called a "mini-motorhome" or "mini." Lengths range from approximately 16 to 32 feet.


The result of warm moisture-laden air contacting cold window glass. Keeping a roof vent open helps to reduce the humidity levels.


A device that converts 120 volt A/C (alternating current) to 12 volt DC (direct current). RV devices mostly run on 12 volt DC power that is supplied by the battery, which allows the RV to function independently. When "shore power" (an electrical supply) is available, the converter changes the voltage from 120 to 12 volt to supply the appliances and to recharge the battery.

Curb Weight or Net Weight

The weight of the RV as it is sitting on the lot, without the personal load you will be adding.


A booth-like dining area in which the table may be lowered to convert into a bed.

DSI (Direct Spark Ignition)

The method of igniting the main burner on a propane-fired appliance. The burner is lit with an electric spark and the flame is monitored by an electronic circuit board. This ignition system is used in refrigerators, furnaces and water heaters.

Ducted AC

Air conditioning supplied through a ducting system in the ceiling. This supplies cooling air at various vents located throughout the RV.

Ducted Heat

Warm air from the furnace supplied to various locations in the RV through a ducting system located in the floor.

Dual Electrical System

RV equipped with lights, appliances which operate on 12-volt battery power when self-contained, and with a converter, on 110 AC current when in campgrounds or with an onboard generator.


A pickup truck, or light-duty tow vehicle, with four tires on one rear axle.

Engine Oil Cooler

A heat exchanger, similar to a small radiator, through which engine oil passes and is cooled by airflow.

Fan Switch

A normally open switch that closes at a preset temperature. It causes the furnace to run for a short time after the thermostat opens, allowing the furnace to cool down.

Fifth-Wheel Trailers

Designed to be coupled to a special hitch that is mounted over the rear axle in the bed of a pickup truck. These trailers can have one, two or three axles and are the largest type of trailer built. Because of their special hitch requirements, fifth-wheel trailers can only be towed by trucks or specialized vehicles prepared for fifth-wheel trailer compatibility.

Furnace Ignition Control Board

When powered, initiates gas valve opening and spark sequence which lasts approximately seven seconds. Newer boards are three try (i.e., will attempt to ignite three times at approximately 60 second intervals). Older models are single try.


An engine powered device fueled by gasoline or diesel fuel, and sometimes propane, for generating 120-volt AC power.

Gray Water

Disposal water from sinks and shower. In some units, this is held in a holding tank separate from black water.

Gross Axle Weight Rating (GAWR)

The manufacturers maximum load weight, in pounds, that can be placed on the axle. If an axle has a 3500-lb. GAWR and the RV has two axles (tandem axles), then the RV would have a Gross Vehicle Weight Rating (GVWR) of 7000 lbs.

Gross Combined Weight Rating (GCWR)

The manufacturers maximum load weight, in pounds, allowed for the trailer and tow vehicle. This rating includes the weight of the trailer and two vehicle plus fuel, water, propane, supplies and passengers.

Gross Trailer Weight (GTW)

The weight of the trailer fully loaded in its actual towing condition. GTW is measured by placing the fully loaded trailer on a vehicle scale. The entire weight of the trailer should be supported on the scale.

Gross Vehicle Weight Rating (GVWR)

The manufacturers maximum load weight, in pounds, allowed for the vehicle. This rating includes the weight of the vehicle plus fuel, water, propane, supplies and passengers.

Heat Exchanger

A device that transfers heat from one source to another. For example, there is a heat exchanger in your furnace - the propane flame and combustion products are contained inside the heat exchanger that is sealed from the inside area. Inside air is blown over the surface of the exchanger, where it is warmed and the blown through the ducting system for room heating. The combustion gases are vented to the outside air.

Heat Strip

An electric heating element located in the air conditioning system with the warm air distributed by the air conditioner fan and ducting system. They are typically 1500 watt elements (about the same wattage as an electric hair dryer) and have limited function.

Hitch Weight

The amount of a trailer's weight that rests on the tow vehicle's hitch. For travel trailers this weight should be 10-15 percent of the total weight of the trailer. For fifth wheels this weight should be 15-20 percent of the total weight of the trailer.

Holding tanks

Tanks that hold water. There are three different holding tanks on most RVs; fresh water tank, gray water tank and black water tank. The fresh water tank holds fresh water that can be stored for later use. The gray water tank holds the waste water from the sinks and showers. The black water tank holds the waste from the toilet.


Connections to a campground's facilities. The major types of hookups are electrical, water and sewer. Hookups may also include telephone and cable TV in some campgrounds. Full hookups refer to a combination of water, electricity and sewer.

Igniter Electrode

Similar to a spark plug. There are two versions; a three probe (remote sense) and a two probe (local sense).


A sandwich of structural frame members, wall paneling, insulation and exterior covering, adhesive-bonded under pressure and/or heat to form the RV's walls, floor and/or roof.

Light Weight RV

RVs that are designed to be easily towed behind most Minivans, light-duty trucks and cars! The most common being a pop-up trailer.

Limit Switch

A furnace safety switch that is normally closed but that opens if it gets too hot. When it opens, it turns off the power to the gas valve and igniter board.

Livability Packages

Items to equip a motorhome for daily living, which may be rented at a nominal cost, rather than brought from home. Includes bed linens, pillows and blankets, bath towels, pots and pans, kitchen utensils, cutlery.

Net Carrying Capacity or Payload Capacity

The maximum weight of fuel, water, propane, supplies and passengers that can be added to an RV without exceeding the Gross Vehicle Weight Rating (GVWR).


A small standby flame used to light the main burner of a propane fired appliance when the thermostat calls for heat. Pilots can be used in furnaces, water heaters, refrigerators, ovens and stove tops.

Pop-up Trailer

Also known as a folding trailer, great for first timers due to its simplicity and relatively low cost.

Propane or LPG (Liquefied Petroleum Gas)

Propane or LP gas is used to fuel appliances in the RV, such as the stove, oven, water heater and refrigerator. Propane tanks are usually rated as pounds or gallons.


Slang for an RV.

Roof Air Conditioning

Air conditioning unit mounted on the roof of an RV to cool the unit when it is parked. When moving, most RVs are cooled by air conditioning units which are components of the engine.

RV (Recreational Vehicle)

A motorized or towable vehicle that combines transportation and temporary living accommodations for travel, recreation and camping. RVs come in all shape and sizes for any budget or need. They range from camping trailers costing a few thousand dollars to luxurious motorhomes with prices well into six figures. RVs refer to multiple RV and RVers refer to their owners.

Safety Chains

A set of chains that are attached to the trailer A-frame and connected to the tow vehicle while towing. Safety chains are intended to keep the trailer attached to the tow vehicle in the event of hitch failure, preventing the trailer from complete separation. They should be installed using an X-pattern (criss-crossed) so the coupler is held off the road in the event of a separation.

Self Contained

An RV which needs no external electrical, drain or water hookup. Thus, it can park overnight anywhere. Of course, self-contained units can also hook up to facilities when at campgrounds.

Tag Axle

A tag axle is typically the axle behind the drive axle and is usually able to be elevated from making contact with the roadway when not needed. A tag axle can also be found on semi trailers. These are also able to be lifted when not in use. This allows the tires to avoid unnecessary wear and also saves fuel. The axle is lowered when it becomes necessary to help spread the vehicle's weight over a greater area.


A device that monitors the pilot flame of a pilot model propane appliance. If the pilot flame is extinguished, the thermocouple causes the gas valve to shut off the flow of gas to both the pilot flame and the main burner.

Toad or Dinghy

A vehicle towed behind a motorhome, sometimes with two wheels on a special trailer called a tow dolly, but often with all four wheels on the ground.

Tongue Weight (TW)

The amount of weight imposed on the hitch when the trailer is coupled. Also referred to as "hitch weight". Tongue weight for a travel trailer can be 10-15 percent of overall weight; fifth-wheel hitch weight is usually 18-20 percent of the overall weight.

Tow Bar

A device used for connecting a toad/dinghy vehicle to the motorhome when it's towed with all four wheels on the ground.

Tow Dolly

A low, wheeled frame with a platform used for carrying heavy objects. Motorhome owners often use tow dollies to haul a car or SUV behind their RVs.

Trailer Brakes

Brakes that are built into the trailer axle systems and are activated either by electric impulse or by a surge mechanism. The overwhelming majority of RVs utilize electric trailer brakes that are actuated when the tow vehicle's brakes are operated, or when a brake controller is manually activated. Surge brakes utilize a mechanism positioned at the coupler that detects when the tow vehicle is slowing or stopping and activates the trailer brakes via a hydraulic system.

Transmission Cooler

A heat exchanger similar to a small radiator through which automatic transmission fluid passes and is cooled by airflow.

Travel Trailer

Also referred to as "conventional trailers" these types of trailers have an A-frame and coupler and are attached to a ball mount on the tow vehicle. Travel trailers are available with one, two or three axles.

Umbilical Cord

The wiring harness that connects the tow vehicle to the trailer, supplying electricity to the trailer's clearance and brake lights, electric brakes and a 12-volt DC power line (to charge the trailer's batteries).


An RV's underfloor surface, which is protected by a weatherproofed material.

Unloaded Vehicle Weight or Dry Weight

The weight of the RV without adding fuel, water, propane, supplies and passengers. The manufacturers UVW will not include any dealer-installed options.

Van Conversion

A fully loaded van and the smallest of the fully enclosed motorhomes. These are constructed on a van chassis with elevated roof lines but no modifications to the length or width of the original chassis. Gross vehicle weights are in the 6000 to 8000 range with heights of 7 to 8 feet and lengths of 17 to 19 feet.

Weight Carrying Hitch

Also known as a "dead-weight" hitch, this category includes any system that accepts the entire hitch weight of the trailer. In the strictest sense, even a weight-distributing hitch can act as a load-carrying hitch if the spring bars are not installed and placed under tension.

Weight Distributing Hitch

Also known as an "equalizing" hitch, this category includes hitch systems that utilize spring bars that can be placed under tension to distribute a portion of the trailer's hitch weight to the tow vehicle's front axle and the trailer's axles.

Wet Weight

The weight of the vehicle with the fuel, freshwater and propane tanks full.


Distance between center lines of the primary axles of a vehicle. If a motorhome includes a tag axle, the distance is measured from the front axle to the center point between the drive and tag axles.


Refers to the "fish-tailing" action of a trailer caused by external forces that set the trailer's mass into a lateral (side-to-side) motion. The trailer's wheels serve as the axis or pivot point. Also known as "sway".