Chill Out
Chill Out typography
man wrapped in blankets in an RV
An annual inspection will help keep an RV furnace in tip-top shape
By Bill Gehr
Photos by the author

ost motorhomes, trailers and truck campers have some form of comfort heating to maintain interior warmth during cold days and nights. The vast majority of RVs use a forced-air furnace complete with a network of ducting that runs through the floor or cabinetry, terminating with registers to distribute warm air.

Unfortunately, annual furnace maintenance and cleaning are often overlooked, which can lead to poor performance, malfunction and even failure. And — you guessed it — problems seem to only crop up when you need heat the most. Annual cleaning is important because the return air system does not include a replaceable filter to prevent dust, lint and pet hair from impacting performance and safety. Following these preventive maintenance procedures will give your heating system the advantage during the cold weather.

Let’s Take a Look
Using a bright flashlight, peer into the exterior exhaust/cold-air intake of the furnace. You’ll be checking for mud daubers, spiders and wasps, any of which can block the airflow in both directions during the heating process. A restricted airway could cause short cycling of the flame or an improper flame from lack of oxygen, leading to an over rich gas-air mixture.

using a flashlight
Use a flashlight to check for mud daubers or other debris inside the exhaust port. It might be possible to use a coat hanger to pick out any obstructions. If not, the furnace will have to be removed to gain access to anything clogging the airway.
furnace return air grill
It’s a good idea to remove the furnace return air grill to check for any debris that might have fallen into this space. In this case, the furnace was mounted in the galley, which can be susceptible to wayward items that have fallen out of drawers and cabinets.
If you discover debris or nests, remove the vent assembly and clean any obstructions. Be sure to replace the gasket or seal before reinstalling the vent assembly. If you suspect a mud dauber has built a nest inside of the blower assembly, you will need remove the furnace in order to gain access to clean out the debris. If you’re not comfortable with removing the furnace, leave this job to professional RV technicians.

The next step is to remove the interior or exterior access panel for inspection. You’ll be looking for lint, dust and/or debris on the circuit board and blower wheel(s). Be careful not to disturb the wiring or compromise any of the components, which could lead to a furnace malfunction. Use a bright flashlight to inspect the interior of the partially hidden blower assembly to determine if a build-up of lint is present. With the help of a long-nose air nozzle, compressed air (at no more than 125 psi) can facilitate the removal of dust in the hard-to-reach areas. Avoid directing high pressure air toward the circuit board or other electrical components (play it safe and adjust air pressure to 20 psi when cleaning the board.)

Thoroughly inspect all of the wiring; it is not uncommon for rats or mice to chew through electrical insulation and conduit. Damage to wiring or other components may require the assistance of a certified RV technician.

Return air vents
Return air vents can be found in various areas in RVs. This vent is cut into the steps that lead to the bedroom in a fifth-wheel. It’s important to keep the area around the return air vent free of stored items. Any obstruction can diminish the efficiency of the furnace.
Next, check the return air vent located near the furnace. Manufacturers of fifth-wheel trailers and motorhomes normally locate the furnace in the basement and the return air vent will be on a common wall inside the RV. The furnace in travel trailers is typically mounted near a galley area compartment with the return air vent directly in front of the furnace. This area is susceptible to towels or other products falling out of drawers that potentially could block the return air vent. Never block the return air vent or install a filter, which can affect the heat cycle and reduce efficiency.
Feel the Heat
Ducting and heat registers play a big role in heating efficiency. Every furnace is designed to function with a specific number of ducting lengths connected to the furnace body, so don’t use adjustable registers or block off the existing registers. Inspect all accessible flexible ducting and replace if compromised. Floor registers are difficult to clean without removing the covers. Any accumulation of pet hair, lint and other items should be removed regularly with a vacuum cleaner crevice tool.
Gas Pains
LP-gas pressure plays an important role during the furnace’s ignition cycle. Not surprisingly, LP-gas regulators deteriorate over time — and any dysfunction will cause improper ignition and air/fuel mixture during the heating cycle. Gas pressure should be checked by a professional technician annually using a tool called a manometer. Not only will this confirm proper pressure, but a leak-down test will discover any breaches in the propane piping and/or fittings. Frankly, it’s not a bad idea to replace the LP-gas regulator every five years. If you are experiencing ignition problems, seek professional help; gas appliances can be dangerous if not diagnosed or repaired correctly.
Inspect all ducting from the furnace for integrity. Cuts or cracks will reduce efficiency because the heat will escape before reaching the registers. Furnace manufacturers require a specific number of flexible ducting runs and/or the use of a plenum. It may be possible to repair small areas with certified metal duct tape, but in most cases the tubing will need to be replaced.
wire inspection
Inspect all the wiring for faulty connections and repair as necessary. Mice and rats consider wire insulation dessert. Vibrations can loosen wire connectors and create issues with furnace operation.
wiring to the circuit board
Also check out the wiring to the circuit board and make sure the connector is tight. Dust and debris can affect the performance of the circuit board.
The Volts Are In
Battery voltage is critical for the proper function of a forced air furnace system. Check to be sure that all the battery terminals are clean and secure. Using an accurate multimeter, confirm power to the furnace, which requires at least 11 volts DC to operate when the blower is running. Should the voltage drop below that in the middle of a heating cycle, the furnace will go into lockout mode and blow cold air unless the circuit board is designed to shut the furnace off. General battery health is also important to keep appliances, like the furnace, running properly.

Obviously, there are other things that can impact RV furnace performance, from broken connections & errant thermostats to parts that simply wear out over time. That said, proper and timely maintenance can oftentimes reveal minor problems before they became a major headache. Hot water bottles have their purpose — but cuddling up to one because your furnace isn’t functioning shouldn’t be one of them.

circuit board
It’s possible to clean out any dust and debris from the area where the circuit board is mounted, but high air pressure can damage the components on the board. Use a long-nose air gun with no more than 20 psi of pressure, using short bursts.
Higher air pressure
Higher air pressure can be directed at any of the solid components, including the blower wheels, which tend to collect a lot of sticky lint resulting from centrifugal force. Generally, it’s always best to keep all the components and housing clean. Don’t exceed 125 psi of air pressure.
toothbrush for cleaning
If the sticky lint is stubborn to remove with air pressure, you may need to use a soft plastic bristle brush or even a toothbrush. Keeping the furnace free of debris and dust will pay off in service longevity.
Registers in the floor
Registers in the floor have a tendency to collect dirt and lint below the grate. Also, copious amounts of pet hair tend to collect in this area. Here is a radical example of debris that has collected in the register ducting over a long period of time. Remove the register grate to provide access for a vacuum crevice tool for cleaning. Obviously, the furnace register must not be blocked with stored items.