Tech Tips: Keeping Warm in Your RV

Winter travel in your RV can be a real treat: The scenery is so different, the crowds are down, and the stillness at night is breathtaking. But on the other hand, keeping warm can present its own set of challenges. What can be done to take the chill off winter’s bite?

While en route to your destination, motorhome folks may have a wee bit of an advantage over towable folks. Just kick up the thermostat on the furnace and let the good therms roll. The engine will keep the batteries charged, and most motorhome folks don’t have the qualms about LP gas safety that the towable set does.

If you don’t have unease about towing with your propane container valves open, having a warm trailer when you get to the other end can be a blessing. Keep in mind, the unholy trinity of size: the size of your trailer (hence the size of the furnace), the size of your battery banks, and the size of the charge line connecting your tow rig electrical system to your trailer’s electrics. Tow package wiring (and the wiring running from the trailer electrical “pigtail” plug back to the “house” batteries) is typically far too small for efficient battery charging.

Let’s say you’ve a fairly good-sized trailer, and the furnace blower chews up seven amps. If you fired up the furnace when you began your day, traveled through cold weather for 10 hours, and set the thermostat for a warm arrival temperature, that furnace blower could really devour the current. The typical, skinny 12 gauge wire, making a run all the way from the engine compartment in your tow vehicle back to wherever your house batteries are installed—and back again—presents a lot of resistance to the flow of power. You may arrive at your camp with barely enough juice to light a bulb. While it’s a whole other subject, beefing up the size of your charge wire may be in order.

Waking Up Warm
Keeping the rig warm overnight while sleeping is a different story, depending on your particular RV lifestyle. If you’ll be overnighting at an RV park or where you’ll have shore power available, the worry about running down your house batteries isn’t a problem. Still, you’ll want to stay warm without busting the bank keeping the propane bottles full.

Take a tip from a couple who has a park trailer, which is one of those oversized RVs that is not meant for travel and is generally left parked. The wall and ceiling construction in their unit is practically identical to most travel trailers, and they have two 30-pound (seven gallon) LP tanks. When desert cold strikes their Arizona retreat, their furnace can chew though the LP at a famous rate. Electrically fired space heaters can help, but they may not be practical. They’ve found a simple electric blanket can really make the difference.

Here’s the skinny: A typical queen-sized electric blanket has a draw of 200 watts, and an estimated duty cycle of 50 percent, meaning on a cold night, the blanket is “on” and consuming 200 watts half the time. For a 10-hour night, that would mean a power consumption of 1,000 watts  (or one kilowatt hour) based on a formula of 200 watts x 10 hours x the 50 percent duty cycle.  A space heater keeping their bedroom warm for 10 hours would consume 1200 watts with a 50 percent duty cycle, or a total of 6,000 watts.  With electricity running about a dime a kilowatt hour, using that electric blanket costs a dime a night, while the space heater costs 60 cents. It doesn’t take long to see the payoff.

But what about those who boondock away from shore power? Could you run an electric blanket through an inverter? From a technical standpoint, that’s not a problem. But can you “afford” it in terms of battery use? Here’s the math for battery power consumption.

Battery amp-hours consumed equal AC watts divided by 10, multiplied by 1.2 (a factor for inverter inefficiency) multiplied by hours of use. So our 200-watt electric blanket works this way: 200/10 x 1.2 x .5 (figuring in the 50 percent duty cycle). The result, a cold night with the blanket will take 12 amp-hours from the battery.

Note this point: Some electric blankets (and bed warmer pads) find electricity produced by a modified sine wave inverter poisonous. Pump a modified sine wave into the blanket controller, and “poof” the controller self-destructs. If you use a modified sine wave inverter, check with your blanket manufacturer before you plug in and try it out. The more expensive, pure sine wave inverter, should not be a problem for your blanket.

So what about using the furnace to keep the house warm, and just go ahead and pay the piper for the propane used?  Here’s where you’ll need to know how much “juice” your furnace blower uses. Let’s go back to our seven- amp scenario we used earlier. Ten hours x seven amps x a 50 percent assumed duty cycle reads out to 35 amp-hours

For boondockers, 35 amp hours for the furnace is likely a “bust the bank” situation; even 12 amp-hours dedicated to an electric blanket may be more than you care to spend. Here’s the other option for both boondockers and shore power users who’d rather limit their consumption of electricity and LP use. Since the typical RV forced air furnace blows a huge amount of the heat right outside the rig as exhaust and consumes vast quantities of electrical power, a more efficient heater is great.

The option is a non-vented LP heat system. Instead of blasting a lot of heat outside, most all is kept inside the rig. Of course this means combustion byproducts are released inside, and oxygen is taken from inside the RV. We’ll cover these safety issues in a moment.

Two types of non-vented heaters are widely used among RVers. Catalytic or “cat” heaters use a specially coated catalyst bed or mat to produce heat flamelessly. Many consider them safer than the other style, the blue flame type. Cat heaters are highly efficient, turning about 95percent of your propane into usable, radiant heat. Because they are radiant, they can take awhile to heat up your rig. They’ll quickly warm up a person in the “direct line of fire,” but  their heat must be absorbed by people or objects, then slowly released to warm the surrounding air.

So-called blue flame heaters, as implied, produce a genuine flame. They’ll warm up the air and the room much more quickly than a cat heater, and many have adjustable thermostats that turn the main flame off and on, whereas catalytic heaters can generally be set only for low, medium, and high, and as such, make it more difficult to keep an even heat. But blue flame heaters do use more oxygen.

Non-vented heaters, both catalytic and blue flame, kick plenty of water vapor out into the air—and into the RV. If you’re already bucking a high-humidity environment, you may find yourself mopping up unwanted condensation. Follow the directions of the manufacturer regarding how much air to bring into your RV. Cracking a couple of windows or roof vents generally meets the need for air.

One heating trick we don’t recommend:  using the cooking stove to take off the chill. There aren’t any protections associated with this method.  Many blue flame style heaters have low oxygen sensors that will shut the gas off if the oxygen level in the RV gets to a point where it could be dangerous to health. Cooking stoves don’t have those kind of “smarts,” and could leave you sleeping—permanently.

Russ and Tiña De Maris are authors of RV Boondocking Basics—A Guide to Living Without Hookups, which covers a full range of dry camping topics. Visit icanrv.com for more information.

Russ and Tiña De Maris