RV Camping, RV Furnace, RV Furnace Troubleshooting, RV Heater, RV heater Troubleshooting, RV Life, RV tech tip, RV Tips, RV travel, tech tip, Travel Tips
Over the years we’ve seen more and more RV enthusiasts not putting their RVs away for the winter or even heading South for warmer temperatures, rather using their rigs for winter activities. I remember some chilly nights at -20 degrees in Fargo ND, a weeklong trip with my own personal “Ski Chalet” in the Rocky Mountains of Colorado, and every February we drag out several motorhomes to use as “green rooms” for bands at the Winter Dance Party in Clear Lake IA!
Whatever your type of winter camping, making sure your furnace is operating at the utmost efficiency is important. Let’s take a look at the different types of heaters used in the RV Market:
RV Heater Types
Forced Air Ducted
For years, Suburban, Dometic, and Atwood Hyrdoflame were the main brands available and they all worked in a similar manner. The thermostat would be set to the desired temperature and when the ambient temperature inside the rig gets to that setting it would create a closed circuit and send the 12-volt power to the module board of the furnace calling for heat. The furnace would start the blower motor which exhausted any old air in the intake, burner assembly, and exhaust port. It also pushed air over the burner assembly to the vents drawing interior air for circulation. As the air flowed over the burner assembly it raised a sail switch in the round shroud and once this switch lifted high enough, it would create a close circuit sending 12-volt power back to the module board indicating there was enough airflow to open the gas valve and start the spark sequence. A forced-air–ducted vent furnace typically has an exterior mount and can only be accessed for service from the outside.
Once the burner was lit, air moving over the burner assembly was heated and distributed through the coach by either flexible ductwork under cabinets or under furniture or by a plenum under the floor to floor vents similar to a residential design.
Forced Air Direct Discharge
This design operated the same as the vented version but is used in smaller units without vents and the air is supplied directly from the vents on the furnace itself. It has a much more compact design and can be accessed from inside the rig.
Another option for heat that has been a source of confusion for many RVers is a heat pump option that is labeled “Electric Heat” on a thermostat. Most heat pumps operate through the roof air conditioner and in simple terms, the unit runs backward and draws BTUs out of the outside air through the coils and evaporator to provide heat inside. These models only are efficient down to about 55 degrees outside temperatures and only supply mild supplemental heat from the 60-65 degree ambient temperature range. The confusing part is the label on the thermostat makes it look like it’s an electric heater that can be used any time you are plugged into shoreline power!
Almost every year I get a call from the group at the Winter Dance Party complaining the heaters don’t work in the units sitting outside as green rooms. In every case they ran the propane out using the forced air heater and switched it to “Elec Heat” and it just blows cold air. That’s because it is 0 degrees outside and there are NO available BTUs for the heat pump! However, it is a good source of free heat in that 55-65 degree range to top off the inside of your coach if you are plugged into shoreline power and not paying extra for it!
Some roof air conditioners have a heat strip feature that does work on 120-volt power which heat a thin wired strip around the perimeter of the shroud inside the roof air conditioner, however, it is not typically enough to keep the rig warm.
In-Floor Heating Systems
Several models have been introduced over the years including Aqua Hot which has an onboard boiler that heats a liquid solution and routes it around the rig to heat the interior and water heater. I have also seen a few electrical versions of a wired-in-floor system using pads with coils but these are usually an aftermarket installation.
Making Your Forced Air Type More Efficient
There’s not a lot of maintenance required with forced air models either vented or non-vented however, there are things you need to understand to prevent issues.
Proper 12-volt House Battery Power
Even though they run on propane, your furnace needs at least 10.5 volts of DC power to the module board for it to open the gas valve and light. The deceiving part is the fan will run all the way down to 4-5 volts so it seems to have power, just won’t light? Most often the issue is a sulfated battery that can’t keep up even when plugged into shoreline power with all the other appliances running as it seems they are fully charged, but drop off fast if sulfated. I constantly get the question, my furnace will not run and my batteries are good? The only way you can tell your batteries are holding a full charge and providing the amp hours designed is to charge them properly, hook them up to a 24 amp draw machine, and count the hours! Since this is almost never done, hooking up a digital meter only tells you the current charge, not the efficiency. If the batteries are sulfated, they will start off at 12.6 volts but drop fast and a low battery will not provide the power needed to get the airflow out of the fan and raise the sail switch, therefore the gas valve will not open and the unit will not light. If your fan is running, but your furnace does not light, hook up a portable booster to verify it has enough power. If it still does not light, read on.
Low LP Pressure
All LP appliances need 11” of water column pressure to operate properly and this is provided by the regulator at the LP cylinder. If you know you have proper 12-volt power and hear the click of the gas valve opening and the spark trying to light and it does not light, the chance is you have low LP pressure. This can be tested at the furnace by a certified technician, or you can do a quick test by turning on a stove burner and watching the flame. It should be a steady blue one. Turn on a second and then a third and notice the flame. Then turn on another LP appliance such as a water heater or refrigerator and notice the flame. Sometimes appliances work fine for a while then stop. This could be a situation where it is the only appliance working and there is enough LP pressure and 12-volt power for one but when the water heater or refrigerator kicks on at the same time, there isn’t enough of one or the other? This little test will simulate several appliances drawing at the same time.
Sufficient Air Flow
Not only does the sail switch need to be raised at the fan motor shroud, but there must be good airflow out of the direct discharge as well as the vents. If you have rugs over the vents or anything blocking the airflow, it will create back up in the furnace could affect the sail switch but most likely create a rise in temperature building up and the high limit switch will shut the unit off. This is a temperature sensor at the far end of the burner assembly as a safety feature. Keep all vents open and free-flowing.
Even though I mentioned earlier there is very little maintenance required, it’s important to make sure there is good airflow in and out of the outside intake/exhaust vents as well as the interior air return. Spiders and mud daubers love propane and heat and will plug the holes needed to bring fresh air into the burner chamber and exhaust outside.
Make sure they are clean and the air is flowing freely. Sometimes it might be necessary to install a screen over the vent to prevent the build-up of foreign material! If your exhaust vent has an abundance of black soot or what looks like a potential extremely hot situation that has created a burned effect, get it looked at by a certified technician.
Also check inside to make sure there isn’t a build-up of pet hair, dust, or other items that can get drawn into the air return for proper circulation.
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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Paul Goldberg said:
My Coleman Mach heat exchangers will keep my 36 foot diesel pusher very comfortable in temperatures down to 40 Deg F. If they stopped providing heat at 55 I would have them serviced. because it would hardly be worth turning them on. I am not an English teacher so I will merely suggest that you turn on a grammar checker before releasing your column to the public.
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Paul Sl Goldberg said:
I note that I used a . where I meant to use a , but the app won’t even let me edit my post.
While I’m at it, there are a series of useful pictures that have no captions or specific references so explain their presence.
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