Winter is upon us and even if you are one of the lucky RVers that goes South for the winter, temperatures can get below freezing and you want the RV furnace to be in tip-top shape. That means doing a little preventative maintenance.

Most RVers take the furnace for granted as there are typically no filters or lengthy ductwork like the residential models. We just turn the thermostat to the desired temperature and wait for the heat to kick on.

Forced air furnaces such as the Suburban and Dometic brands have either ducted vents going through the rig, or direct airflow coming from the unit. They all operate fairly similarly and should have some basic maintenance performed occasionally.

How The Furnace Works

When the temperature drops to the set point on the thermostat, 12-volt power is sent to the module board on the furnace which starts the fan or blower. It is important to have fully charged house batteries or plugged into shoreline power as the blower motor will start but the gas valve will not open unless there is sufficient power to provide airflow, more on that later.

The fan draws outside air in through the vent purging the burner chamber and exhausting it outside so no outside air enters the rig. The fan also draws interior air through the cold air return and routes it over the burner assembly, past the sail switch, and out to the vents. This air-lifts the sail switch until it gets to the “closed” point, which sends 12-volt power to the module board letting it know there is sufficient airflow and to open the gas valve. Low batteries or insufficient airflow will not lift the switch to the closed position and therefore the furnace will not light. However, it will continue to blow cold air until the battery goes completely dead.

Once there is sufficient airflow and the sail switch gets to the closed position, the gas valve opens and the spark ignitor lights the furnace.

It is important to inspect and clean the exterior intake and exhaust vents so there is no obstruction. Mud daubers and spiders like the smell of propane and can clog up the vent and restrict airflow. There are even aftermarket screens available that will help keep them out without restricting airflow.

Make sure all vents and ductwork are clear and there is good airflow. Do not cover or close vents inside the rig as this will reduce airflow and keep the sail switch from rising or even increase the temperature at the furnace which would create the limit switch to shut off the furnace. Make sure any ductwork weaving through cabinetry or under the sofa is not kinked or obstructed.

If you see excessive black soot on the outside exhaust vent, it could be a sign of improper combustion due to low LP pressure, improper air-to-LP mixture, a dirty burner chamber, or other issues. It is a good idea to have the furnace cleaned and inspected periodically by a certified RV Service Center.

Supplemental Heat

Keep in mind that your RV furnace can only provide a limited amount of heat and trying to heat the entire rig as well as the lower compartments in basement models may not be possible. Using a supplemental heating system helps customize the heat zones and extends the LP life as well. Catalytic heaters such as the Camco Olympian or Mr. Heater allow you to drop the overall temperature down to 60 degrees or lower and just heat the portion of the RV you are using such as the living room during the day or bedroom at night. No need to keep the entire rig at 70 degrees.

These heaters are safe and produce very little moisture or carbon monoxide. They can be portable using the small LP cylinder or hard plumbed to an existing LP system.

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About the author: Dave Solberg: Managing Editor, RV Repair Club

For the last 25 years, Dave has conducted RV maintenance and safety seminars, developed dealer and owner training programs, written RV safety and handyman articles authored an RV handbook reference guide, and logged over 100,000 miles on the road in an RV.

RV Repair Club is your go-to online resource for enthusiasts who want quality RV maintenance, repair, and upgrade information – a community where passionate RVers can come together to gather knowledge and share their experiences.

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