RV Furnace Basics and What to Look For

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One of the best parts about camping in an RV instead of a tent is that you can do it all year round. While in a tent you’re subject to the whims of Mother Nature, but your RV will always be cozy because of insulation and a working furnace. Much like a house furnace, an RV furnace has a central spot that creates the heat and a series of ducts or tubes that carry the warm air into the various parts of the interior. This basic design exists whether you’ve got a large motor home or a smaller trailer version.

Like any other system, your RV furnace needs occasional maintenance, but it’s a minimal contribution for this appliance. There’s not much that can go wrong on an RV furnace that’s actually fixable by the average owner, so checking for problems is going to be your biggest chore and contribution.

In this video, you’ll see how to access the furnace underneath your RV body. You’ll see visuals of how the different types of duct work transports the warm air to the colder parts of the interior. An RV furnace needs both battery power and a fuel, such as propane to function. We’ll also talk about the minimum amount of battery power needed to keep your RV furnace running. If your RV furnace isn’t working right, there are things to check, and you’ll learn about them here. Find out how to troubleshoot problems with the exhaust, and even how to take apart the thermostat and cross wires to double check the sparking mechanism that starts the furnace underneath.

Discussion
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23 Responses to “RV Furnace Basics and What to Look For”
    • Customer Service Techs

      Thanks for visiting the RV Repair Club site. To provide
      more specific information to help with your issue we would
      need the make, model and year of the heater as well as the
      RV.
      Here are a few basic troubleshooting tips to start with.
      The pilot will not light if the batteries are below 10.5
      volts. It’s a little deceiving as the blower will run,
      but will not light for safety reasons. So check your
      voltage at the house batteries first. Verify you have
      proper LP flow by testing the stove top if you have one?
      See if it lights and you have a good, steady flame.
      Also, there are some great videos in the Heating and
      Cooling section of the RV Repair Club.
      Hope this helps.

      Reply
      • SEAN

        I have a 06 Bighorn 3600rl. It has a 35000btu suburban furnace. Model #SF-35 …. The blower wil not come on. I can hear the electronic ignition kick on. But no blower. This is the second time this has happened. First time RV Tech came and fixed it. Where do I start to figure out what’s wrong with it?

        Reply
        • Customer Service

          Hi Sean. Thanks for visiting the RV Repair Club and the opportunity to assist with your furnace issue. Sorry for the delay, however I wanted to make sure I reviewed the issue and sequence of events with the proper technicians as it seemed a little strange that you would not hear the blower motor start but did hear the electronic ignition? According to Suburban, this should not happen? The blower motor/wheel should be the first step of operation to ensure there is proper voltage to the system before closing the sail switch then opening the gas valve and sparking the ignitor! You might be hearing the relay on the control module trying to start the blower motor? The first step would be to check for proper voltage. You need 10.5 volts to the unit for it to operate. Also, you could have a dirty or faulty sail switch? There is a video in the Heating and Cooling section on Troubleshooting and RV Furnace and checking voltage. It would also be a good idea to take off the vent cover and verify if you are actually hearing the gas valve opening and the ignitor trying to spark rather than the blower wheel or relay. You should be able to see the blower wheel with the cover off.

          And finally, if a technician did work on the unit, what did he do and isn’t this a warranty item?

          Reply
  1. keith

    my furnace runs for about 1 minute and then shuts off before it reaches set temperature. if i reset and restart the furnace it does the same thing.

    Reply
    • Customer Service

      Hi Keith. Thank you for visiting the RV Repair Club site and the opportunity to assist with your furnace issue. To provide accurate technical information, we need to know the make, model, and year. It’s either a Suburban or HydraFlame.

      Reply
  2. Sheryl A Wahl

    Our furnace is working BUT we had a visit from the fire department! a visitor smelled gas in our trailer therefore the air was checked! We had to move out! I noticed that their is a LOT of black soot around the outside of the trailer where the furnace is! We live full time but are very new to maintenance, that why I joined RV repair Club. Can someone help or direct me to where I should go from here? I need to be able to fix this myself, due to finances. Thank You!

    Reply
    • Customer Service

      Since gas was detected in your rig and you had the local fire department check the rig and initiate an evacuation the furnace or whatever appliance is causing the air quality issue must be checked by a qualified technician and certified as repaired? You would need specific equipment to check water column pressure, LP leak detection, and the ability to check readings on components. This must be inspected by a certified technician.

      Reply
  3. Bonnie

    We own a 2015 Keystone Avalanche 331re and currently cannot get the furnace to operate. The thermostat setting is ok, the propane flow is good but no ignition on the furnace. Could you please reference what to search for that could possibly be a simple fix.
    Thank you
    Bonnie Knox

    Reply
    • Customer Service

      Hi, Bonnie. I would suggest starting with the house batteries as the unit needs at least 10.5 volts and sometimes more to open the valve and start the unit. Next would be the thermostat, they get bounced around pretty good out on the road and it doesn’t take much to have wire break. Take the cover off and if your thermostat only controls the heater, jump the wires to see if it starts. If it controls the heater and AC, then jump the +R with white. Next, check the furnace to see if it is trying to spark by listening for a ticking or spark attempt. Sometimes the ceramic house of the spark assembly gets cracked and the spark travels along the crack rather than to the burner assembly. This is called carbon tracking. Also check the fuse at the distribution panel and check your control module to see if it has one there as well. Those are the quick and easy fixes, otherwise you’ll have to get a multimeter and start looking at the sail switch and other components. These are covered in the furnace troubleshooting video.

      Reply
  4. John Holbrook

    Furnace working well. But a lot of heat is coming out of exhaust outside unit. Seems to be such a waste of heat and fuel.

    Reply
      • Customer Service

        Hi Rui,

        Yes this is how all furnaces work. The heat being made from the flame is inside a combustion chamber. For the flame to light, there has to be a good air-to-gas ratio. New air has to come into the combustion chamber to keep the flame lit and the fumes from the flame burning need to exit out the exhaust. The heat coming out has already heated the chamber. The air coming into the camper is actually air being pulled over the combustion chamber and into the unit. As air is pulled over, it quickly gets hot and then blown through the ducts. It may seem like the heat coming out is wasted, but it has already done it’s job at that point.

        I hope this information was useful!

        Dan
        RV Repair Club Video Membership

        Reply
  5. JUAN N RODRIGUEZ

    I have 2 Atwood Excalibur 8500-III series propane furnaces. One works fine but the other is hit or miss. It seems that when the outside temp is below freezing it doesn’t come on. Sometimes when the temp warms up it will work later in the PM.The light on the thermostat for that furnace comes on but nothing happens. What could be going on? Thanks

    Reply
    • Customer Service

      Hello Juan,

      To diagnose the issue with your furnace we need to know what is happening at each sequence of operation. Here is how the Atwood furnace works:

      The thermostat calls for heat when the temperature drops below the setting and a circuit is closed sending the request to the module board. The module board then starts the blower motor which pushes air into the burner chamber. This lifts a sail switch at the front of the chamber, once this sail switch gets to a certain height, it also creates a closed circuit which tells the module board there is sufficient air flow to light and the gas valve is opened and the spark ignitor lights the burner assembly. Hot air is then blown through the burner chamber to the vents inside passing over a high limit switch at the end of the burner chamber. If a vent inside the rig is closed or blocked with a rug and the air is restricted, the burner chamber gets to hot and the limit switch shuts the unit down.

      So if furnace #2 is not working, check the fuse at the distribution center, the outlets, and it could be low gauge wiring that will not send the signal at colder temps!

      Thanks,
      David RVRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      https://go.rvrepairclub.com/C11081

      Reply
  6. ELMA PEREZ

    we have never use our furnace. I bought a 1994 sportsmens travel trailer. everything else works great. but we have no idea how to turn on the furnace. any help in this area is most welcome. God Bless

    Reply
    • Customer Service

      Hello Elma,

      To provide more specific information on the operation of your furnace we need the make and model of the furnace, however the three that were generally used in the early 1990’s are Suburban, DuoTherm, and Hydroflame and they have a similar operating pattern. Some did have zones with temperature sensors in the bedroom and other places but here is the basic operation. The thermostat calls for heat when the temperature drops below the setting and a circuit is closed sending the request to the module board. The module board then starts the blower motor which pushes air into the burner chamber. This lifts a sail switch at the front of the chamber, once this sail switch gets to a certain height, it also creates a closed circuit which tells the module board there is sufficient air flow to light and the gas valve is opened and the spark ignitor lights the burner assembly. Hot air is then blown through the burner chamber to the vents inside passing over a high limit switch at the end of the burner chamber. If a vent inside the rig is closed or blocked with a rug and the air is restricted, the burner chamber gets to hot and the limit switch shuts the unit down.

      Thanks,
      David RVRC Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      https://go.rvrepairclub.com/C11174

      Reply
  7. Kathy ROARK

    I bought a used weekend warrior toyhauler with Suburban/Duo-therm unit.
    On attempt to turn on heat, a horrible screeching began and continued even after I turned it off at the thermostat.

    Reply
  8. Time kinder

    I have a 2017 Winnebago 37fl .my gas heater works great until it drizzles.then it furnace will start run a shot time the gas shuts off and the fan runs. As soon as the weather improves then furnace works great. Any ideas?

    Reply
    • Customer Service

      Hello Tim,

      Without being able to put a multimeter on the 12-volt input to the module board when this occurs, my guess is your house battery is weak and not providing enough power? Even if you are connected to shoreline power, the batteries will drop to 10.5 volts before the converter kicks in to charge at 13.6 volts. When the temperature drops below freezing, the furnace will work twice as hard and drain the batteries faster. If your batteries are sulfated, they will seem to be charged at 12.6 volts, but will drain much faster than the 85 amp hours they are supposed to provide or more for a higher group rating. When you thermostat calls for heat, the blower motor starts and blows air over the heat chamber. A sail switch is raised to tell the module board there is sufficient air flow and the spark ignitor starts the flame. If you have low house voltage, the blower motor runs slower and does not raise the sail switch so it will not ignite. I would assume when the temperature is above freezing, the furnace doesn’t work as much and the battery gets recharged by the converter before the furnace needs to start. When the temps get colder, the furnace drains the battery faster and the blower motor does not have enough speed to raise the sail switch?

      Thanks,

      David
      RV Repair Club Video Membership

      We’d love to have you be a part of our community. We are convinced you will enjoy the benefits of becoming a member and having access to the best instructional how to videos and professional tips. We would like to offer you a special promotion for your first year membership.
      https://go.rvrepairclub.com/C12078

      Reply
  9. Denise

    We have a 2005 Jayco 3100SS. Just filled the lp gas and turned my remote that operates unit to furnace. Waited a minute or two and no heat. Turned unit to cool (a/c) and it comes right on. Currently RV is parked at my home, plugged up to house electric (15 amp). Was away this weekend, plugged into a 30amp and furnace still wouldn’t work. Haven’t used the furnace in a year or two since we usually use RV during warmer months. Any ideas/thoughts on why this is happening?

    Reply
  10. Bernie Amig

    Have an Atwood 8940-III furnace in a Rushmore 5th wheel. Sometimes the furnace works ok. Sometimes it blows the 15 amp fuse. Sometimes it’s running and the fan slows down and drops the sail switch. If I lower the thermostat it goes into cool down mode and the fan speeds right up to normal. I measured the fan amperage at 9 amps when it’s running fast. Didn’t get to measure it when it’s slow. Measured the input voltage to the furnace. Normally 12 + volts. Fan running slow it drops to 6 or 7. Replaced the converter – didn’t help.

    Reply

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