The Quest for Fume-Free Heat
The photo above might rightly lead you to suspect that this will be the weirdest blog post ever, even on this website. That’s saying something. It was pulled from the 1919 edition of The Gasoline Automobile, which was one of a few efforts to attempt to capture what was a very rapidly changing state of the art. The odd part is that I’ll be referring to it later.
But let me shift gears to the true goal of this post. Heat. Extraordinarily clean heat.
Getting heat in RVs is no problem. You can turn on the built-in furnace for pollutant-free heat (as measured in the interior), or use heat sources that use propane, kerosene, or what-have-you. The square footage of most RVs is usually big enough that you won’t asphyxiate yourself with carbon monoxide, though the unholy stink of kerosene is notable.
Getting heat in a van or truck camper is a little more involved because of the small air volume and lack of clearance for truly hot sources. You’re more likely to either asphyxiate yourself or to set something on fire. Relatively “clean” and safe heat becomes more important.
Where truly clean heat becomes essential is when you’re so sensitive to airborne toxins, molds and pollutants that you get sick. Not just feeling bad sick, but slow death sick. Why would you live in an RV if you were this way? Because of off-gassing in housing materials, hidden mold growth, diesel emissions and agricultural insecticides. The RV – at least a van – allows you to choose interior materials, and then locate and stay in areas which will keep you healthy and ambulatory, and do so almost affordably while you try to get your life back together. The “almost affordably” is important, because you often wind up spending all of what would be your rent money on doctors, prescriptions, therapies, and gasoline.
The problem is that most conventional RV heat sources pose an instant problem for such folks because of combustion gasses, and the easy answers can prove to be no real solution for many. Even the much-vaunted Mr. Heater Buddy, one of the least emissive types around, proved an instant problem in a test. “Just live in a real RV with its built-in direct-vent furnace” poses the issues of money and construction materials. “Just use an electric heater” is a nice thought, but it assumes unlimited funds for truly massive battery banks with either solar power or gasoline generator, or the money for commercial campsite rent. Simply bundling up is helpful, but not a complete solution for folks with other heath issues going.
I’m currently in Yuma Arizona, often billed as the warmest place in the U.S. It can still get into the mid-30s overnight here, and without heat, getting up during the night or in the morning can be an issue. What is needed is something to at least break the chill. On cold, windy and rainy days, it would be nice to be able to get out of warm covers and actually do something other than waiting for better weather.
As applied to a van converted into a living space, two approaches came to mind when I became aware of this challenge. One was to simply punch a hole in the side of the van and install a wall-mounted, propane-fired direct-vent heater, similar to what people install in rural cabins and room extensions. These use a heat exchanger to transfer the majority of combustion heat to interior air, venting the exhaust gasses outside. The issues with these are that the smallest I found is about 8,000 BTUs, four times more than is appropriate for a van. Additionally, the front surfaces get extremely hot, posing a burn and damage hazard inside the tight confines. For one who is ultra-sensitive to off-gassing, the first few days of operation would likely make the van uninhabitable while the paint on the heat exchanger burns off.
The second concept was one relying on hot water, similar to hot water radiator heat in a house. All combustion takes place outside, heating water which is then pumped inside to a radiator. Your vehicle already has one of these of course: the heater. The hot engine coolant is routed to a small radiator called the heater core. A fan blowing through it pushes the resulting hot air toward your freezing little piggies. Unfortunately, firing up a 150-350 HP automobile engine every time you want heat is an extremely expensive proposition in more ways than just fuel cost. Plugging an alternate heat source into the coolant system won’t be practical either, because it would require isolating the heater core to avoid losing heat to the cold engine. An entirely separate system is needed.
There are two similar possibilities here, differing in performance, cost, weight, and installation. Basically, all you do is take some form of propane-fired water heater, and plumb its hot water output to a radiator in the van’s interior. The combustion remains outside, and the heat exchanger remains inside. Unfortunately, this article is not a how-to, as in how to build a proven, ultra-clean heating system for a small dwelling. It is theory only, and I lack the time and inclination to actually piece together such a system. I mention here a few things to consider if you decide to transform such a concept into a working, practical system. I mention them because not being aware them can drastically affect the outcome. With some things, it’s best to look for potential problems early and work up some potential solutions before plunking down hard cash. No sense in wasting time and money.
The first system I envision is a standard-issue propane-fired 5 or 6-gallon RV hot water heater, which can be either conventionally-mounted into the van in a sealed compartment, or remain loose on the ground entirely outside. Propane from a bulk tank must be passed through a common RV-style gas pressure regulator first. Depending on heater type, it will require either a lit pilot light or a source of 12-volt power for the flame ignitor. Hot water is pumped from the heater’s reservoir to an automotive heater core or radiator inside the van via a combination of flexible and insulated rigid tubing with quick-connectors, using a common RV 12-volt water pump for flow. Cooled water is likewise recirculated back to the heater in a return line. A 12-volt fan blowing through the radiator speeds up heat transfer and helps distribute warm air inside the van.
The nice parts of this are that the water heater will automatically try to keep the water at 135 degrees, firing back up and shutting down on its own until manually switched off. A second switch for the water pump lets you extract the last heat from the reservoir before shutting down, or stop active interior heating while maintaining “ready-to-use” hot water in the tank. The tank is already insulated, and can hold hot water for perhaps 6 hours if needed. It takes 10-15 minutes to get water up to temperature, which isn’t too bad. Common automotive radiators and heater cores can be used without much consideration other than sheer size, which equates to an ability to shed heat.
On the downside, the radiator or heater core chosen needs to be good-sized, because this isn’t a big engine rapidly pushing out large volumes of boiling water. It’s just 135 degrees (at best) in a limited volume, so extracting a reasonable amount of heat will tend to need larger surface radiator areas. For rapid van heating, there isn’t much point in returning fairly warm water right back to the tank reservoir. Go too big, though, and the radiator is wasting a lot of space on room-temperature liquid. Not being an engineer, the “too big” cutoff point is hard for me to guess at.
There are plenty of other concerns. A compartment-mounted water heater can boost efficiency and convenience because of short interior rigid pipe runs, and the comparative ease of deploying the system: make sure it’s full of water and throw a switch. But even if the heater compartment sealing to the interior is perfect, wind direction can drive combustion gases through door and window seals, or small leakages in the body structure. The water heater should always be on the vacuum side of the wind. Even a water heater tethered on the ground some distance away poses this problem, but to a much lesser degree. The tethered heater’s problem is weight. At 8 pounds per gallon, a six-gallon heater can be a chore to load and unload. Heat losses through the longer hoses are an issue, and those hoses must disconnectably pass through the vehicle’s body structure.
Pumping water can take as much as 2 amps of power, so pump choice becomes an issue as well as how to replenish the source of that power. Suddenly, you need a good-sized deep-cycle battery and either solar power or a generator. That gets expensive and absorbs more space. Further, modern RV water pumps are triggered by pressure, or rather a lack of it. Open the tap, and they turn on and start pushing water. This may indicate that the heater’s entire water system may need to be left open at its highest point in order to avoid a pressure buildup that would disable the pump. If that proved to be a valid concern, where and how to vent the opening might rule out the possibility of using antifreeze in a compartment-mounted system. A full-external heater would allow only for water as the medium, since hose connections would be regularly opened up.
The easy solution for pumping, in implementation, carries a couple of caveats with it. The solution is to circulate water not with a power-hungry electric pump, but with nature’s own flow technology called thermosyphoning. Hot water weighs less than cool water, and rises. Cooler water descends. The thermosyphon system was used in automobiles until horsepower increased and customer expectations rose. In this system (as in the photo above), hot water from the engine naturally rises through a pipe to the top of a radiator. The radiator, being cooler, cools the water and it becomes denser. This accelerates as the water flows down to even cooler areas. Once it hits bottom, it is pushed back into the engine by the descending water behind it. Many early cars accentuated water return to the engine by placing the radiator quite high, so the cooled water could continue to descend to get to the engine. No pushing was needed for the return.
Superb! Just place our radiator or heater core higher than the water heater, and put the hot water pipe to its top inlet and the return line to its lower outlet. Flow, right? Probably not, or not very much. Thermosyphon radiators were direct, vertical flow – the cooling tubes inside all ran straight up and down. Modern radiators are cross-flow because a water pump allows for this more efficient use of space and cooling capacity. When you lack a pump, a cross-flow radiator imposes way too much fluid drag. Other than buying an expensive Ford Model T reproduction radiator from a specialty vendor, I’m not sure how to overcome this problem. Likewise, selecting a heater core instead of a radiator must also be done carefully. The inlet and outlet must be as far away from each other as possible, and flow between them must be as direct as possible. Oriented with inlet at the top and outlet at the bottom, such a core must be as tall as possible and as narrow as possible as the main tube snakes its way from top to bottom. The goal is to allow a little side to side flow as water descends, but eliminate any core that insists on up and down flow. The guy at the parts counter won’t love you.
The other concern with thermosyphon systems is that they must be kept absolutely filled in order to work. That means up past the upper hose inlet. Letting them run low simply prevents the recycling circulation, and the radiator gets no heat at all.
The second basic approach to the heat problem is to adapt a propane-fired portable shower unit instead of an RV water heater. These are less expensive, far lighter, heat water much more rapidly, and some come with electric pumps. Whether they come with pumps, batteries to run them, the ability to take 1-lb propane bottles or 20-lb bulk tanks is something that will need to be worked around in any case. My concern with them is that their temperatures are of necessity even lower than an RV water heater. They also need to be adapted to longer runtimes, and I don’t know how many cycles they’re engineered for. In other words, for the lesser cost, how long will they last? I have no idea. But they are still very tempting, especially as a way to prove out the concept at minimum cost.
Being more comfort-oriented, I personally would like to dump the whole radiator/heater core thing and pump the hot water through heated tubes below thin flooring of some kind. Slap some thick insulation under that first, and it could mimic residential heating. Certainly not that fastest system in the world. Oh well. Your comments and input are welcome on this post as always. What have I missed? Just don’t say, “a hot water bottle works fine for me”, because it isn’t still hot at 2 AM or 6 AM when duty calls. What would work fine for you two or three hours before sunrise, if you were financially challenged and jammed inside a van? Just throwin’ it out there…