Product Spotlight: Precision Temp RV-500 Tankless Water Heater

Two common concerns with recreation vehicles that are (or should be) familiar to just about every RVer on the road today are weight and resource conservation. Carrying excess weight in any rig has distinct disadvantages. In fact, I’m not sure there are any advantages to running an overweight rig down the road. From tire life to running gear to steering/towing/handling issues, shedding excess weight when possible all rack up on the “plus” side of the column. Likewise, conserving onboard water, battery power and LP gas have to be foremost on the mind of even the most casual RVer, especially when enjoying the adventures of dry camping.

Not often does a single product come along that can do all four; reduce weight, save water, use little battery current and consume almost half the normal amount of propane, especially when found in an appliance such as a water heater. But that’s exactly what the RV-500 tankless water heater produced by Precision Temp accomplishes. I’d heard good things about the RV-500 for a long time. I’ve studied the specs and read all the literature, but never had the opportunity to actually install a brand new unit, until now.

 I’ve known for years that the RV-500 was the logical replacement for any 10-gallon RV water heater, but was surprised to learn that with only a slight modification to the height of the cutout size in the sidewall, it can easily replace all those aging 6-gallon units still out there. But why would anyone choose a tankless water heater in the first place?

Well, less weight being one of major draws. Considering that water weighs 8.35 pounds per gallon, that means you can immediately eliminate almost eighty pounds of unnecessary travel weight when replacing a 10-gallon, DSI (direct spark ignition) Atwood heater and a whopping 90-pounds when replacing a like-size Suburban water heater. Over time, your tires and suspension components will thank you.

For those unfamiliar with how a tankless water heater actually operates, allow me to elaborate. First of all, there’s no tank, duh! There’s also no pilot flame since the RV-500 is a direct spark ignition appliance. The high performance, 12-orifice burner will only ignite when water is flowing. Here’s how it works; when the unit is first powered up by applying 12-volts DC, the integral microprocessor readies the gas valve and puts the operational sequence in stand-by status until a hot faucet is opened somewhere in the coach.

Once water starts to flow, (by either city pressure or onboard pump pressure), a small rotary flow meter is activated and begins monitoring the actual flow of the cold water coming into the RV-500. Once it senses a steady flow approaching one-half gallon per minute, a signal is sent to a modulating LP gas valve, opening the valve and starting the automatic spark igniter. Like most other DSI appliances found on RVs, the control board performs multiple functions; opens the gas valve, creates the spark that ignites the incoming fuel and monitors the flame to ensure the LP is indeed being consumed at the burner.

The microprocessor constantly calculates the amount of water flow as well as the temperature of the incoming water and adjusts (modulates), the LP flow through the gas valve accordingly. This modulating of LP inside the gas control valve makes for a very efficient LP-burning appliance. It only consumes what it needs in order to maintain a set delivery water temperature.

As the incoming water passes through the heat exchanger on its way to your shower or sink faucet, the temperature is monitored by three thermistors positioned at various points along the route. The one pictured here, (the compression nut with the black insulation), is positioned about half way through the heat exchanger. There is another one monitoring the water temperature at the cold inlet and yet a third mounted at the hot outlet.

The processor also interprets this information and recalculates the amount of LP flow needed to maintain a consistent output water temperature within (+ or –) two degrees F. The thermostat, by the way, even though preset by the factory at 115-degrees, is adjustable to any set point between 90 and 135-degrees F. As long as you have that hot faucet open, hot water will continue to flow. The burner shuts down when water flow is stopped. No more running out of hot water just before you rinse the shampoo!

LP appliance safety is always a concern on an RV. The RV-500 is equipped with multiple safety features including two electronically operated over-temperature sensors that will shut the sequence down if exceeded, as well as a thermal ECO (energy cut-off), which is automatically resettable.

A redundant solenoid controls gas flow. The gas valve closes in less than one second if no flame is sensed upon initial ignition of each sequence. The circuit board will try twice for ignition, and then go into lockout. A lockout condition means something is amiss; low or no LP pressure, insufficient voltage, etc.

There is a typical pressure relief valve (P&T) common to all water heaters. And like standard RV water heaters, all combustion takes place outside of the living section, with primary air intake and exhaust gases all sealed from the interior of the RV.

 A covered, 3-amp, in-line fuse accessible through a removable side port protects the internal 12-volt DC wiring. It is recommended to install another fuse in the switch circuit to protect it and the conductors between the voltage source and the RV-500.

The microprocessor and electronic circuitry, including two operational LEDs, are contained in a handy drawer that easily pulls out for maintenance and inspection, accessible from the exterior of the RV-500. About the only maintenance requirement I see is to clean the contacts on the circuit boards once a year.

Replacing an existing tank-type RV water heater is pretty straightforward. After draining the tank, the 12-volt DC wires, hot and cold water lines and LP copper tubing must be disconnected, protected and moved aside. The RV-500 will slip right into the same hole as your current 10-gallon heater. It will likely be necessary to reroute the LP tubing, however. Conveniently, the RV-500 has a rear and a side option for connecting the copper tubing to the inlet flare fitting on the gas control valve.

The 12-volt wires and the hot and cold water lines attach at the rear of the water heater, much like they all do. The only wiring modification may be to reroute the hot wire, either from the existing master switch or run a new conductor from a newly installed switch, plus the negative, ground wire.

If you’re replacing an existing non-wired, pilot-model water heater, be sure to use 18-gauge wires for the hot and ground circuits at a minimum (I recommend 14-gauge). And protect the switch and power circuit with a 3-5-amp fuse or circuit breaker as previously mentioned.

One difference with the water tubing connections on the RV-500, is that the hot and cold are reversed, top and bottom. On a typical RV water heater, cold water enters at the bottom of the tank. On the RV-500, the cold water enters at the top and the hot water emits from the bottom. Of course, if you happen to install it the other way around, you’ll soon find out! Thankfully, I didn’t have that problem since both water connections are clearly labeled! Any RV handyperson should be able to easily replace a standard, tank-type water heater with the RV-500.

The good (quality-wise and customer service-wise), suppliers in the RV Industry freely post their technical literature. And Precision Temp is one of them. Technical specifications, installation manuals, user’s guides, etc., are all available on-line, but are also shipped with each unit. They cover the full spectrum of installation options as well as all the nuances of safety. As with all LP appliances, it is necessary to check all connections for leaks prior to putting the appliance into service. Take the time to read all the paperwork!

I do recommend that the LP system, not just the connection at the heater, but the entire coach be leak-checked by having a certified RV technician perform a timed pressure drop test. Additionally, this appliance, like all RV appliances, must be fed a steady diet of LP delivered at 11.0 water column inches. A manometer and a specific set of procedures are necessary to set the LP delivery pressure and to test the rig for leaks. Rely only on a Certified or Master Certified technician to perform these procedures.

Though the RV-500 was designed initially for use in a recreation vehicle, I chose to install it in what’s called a “tiny house.” There is a distinct “tiny house” movement going on that is quite cool to say the least; basic, simplistic living at its best! Try Googling “tiny house movement” and spend the next few hours (or days) perusing the growing popularity of this social phenomenon.

The installation of the RV-500 in the tiny house is the perfect marriage of sorts. A small dwelling with simple accoutrements simply does not need to house six or ten (or twelve) gallons of water in the water heater. Aside from the RV market, it wouldn’t surprise me to see the RV-500 installed in more of the tiny houses within this growing movement. To read the story about Zoey’s tiny house, go to: http://www.togetherweareone.com/building

As with the tiny house movement, RVers everywhere have long embraced the practicality of sustainable living; that’s exactly what self-contained RVing is, right? Without a doubt, the tankless, instantaneous water heater is here to stay. As a matter of fact, as I type, another product supplier has jumped on the tankless water heater bandwagon, albeit far behind the efforts of Precision Temp. And as more RV manufacturers become more weight conscious, and with eight million (maybe more) RVs on the road in America, I believe Precision Temp just may be busier than ever!

Your homework assignment starts here: http://www.precisiontemp.com/pt_rvmd_main.html

And remember, RVing is more than a hobby, it’s a lifestyle!

Troubled by RV Doc Response

I have trouble with your answer about the check valve on water heaters you addressed in an earlier question. I am sorry, but I have never seen one on the cold water line. The only ones I have seen have been in the hot outlet on the tank. Norman, (Milford, NH)

Norman, you'll find a backflow preventer oftentimes at the cold water inlet, right at the back of the water heater. It's preferred by many of the better manufacturers in order to prevent hot water from migrating back out through the cold inlet. Here's why; If a branch cold line is tee'd into the fresh water system right at the water heater, it could siphon hot water out of the heater and into the cold system. I've seen a few RVs with the water heater located in the lavatory, under a cabinet and in close proximity to the toilet. The customer would get hot water (and steam!) rising from the toilet if he flushed the toilet with hot water in the heater. They thought the cold line to the toilet was plumbed incorrectly but by adding a check valve at the cold inlet, it rectified the "steam in the toilet" issue.

Not all RV manufacturers install a backflow preventer or check valve in the cold inlet because of the added cost and the fact it is not a code requirement, but some do as an added benefit to the end-user. It's a good thing, so let not your heart be troubled any longer!

Travel Trailer Tires

It's time to replace my trailer tires. Installed from the factory are LT235R85/16's. I've been told to get those LT tires off there and replace them with ST tires. If ST rated tires are the best for trailer service, why did the manufacturer use LT rated tires? We have a 34-foot Montana 5th wheel rated at 12,100 pounds. I've heard good and bad about both types of tires. What’s the real story on this question? Leonard, (Kansas City, MO)

Leonard, LT stands for “Light Truck”, ST stands for “Special Trailer.” Although both tires are rated for trailer use, there are distinct differences. For passenger tires (including LT tires), ride, traction, and handling are the key design elements and are all achieved primarily by adding flex to the sidewall. This maximizes tread contact with the road, thus increasing traction and allowing the driver to maintain better control over the vehicle. For trailers, sidewall flexing is not a desired effect because it can be a cause of trailer sway. The stiffer sidewalls and higher operating pressures common with ST tires helps control and reduce the occurrence of trailer sway.

For travel trailers, it is important to match the tires to the application and payload. Since ST tires are constructed with heavier materials, they are tougher and more bruise resistant than typical passenger car tires. This is a plus because trailer suspension systems are generally stiffer and less sophisticated than automotive suspension systems. A tire designed to operate in the more demanding trailer environment will provide you with longer service life and be able to withstand the added abuse trailer tires tend to be subject to.

Bottom line, trailers are more stable and pull better on tires designed specifically for trailer use and I recommend that you switch to the ST type. The manufacturer likely used LT tires because they too are rated for trailer use and are simply cheaper than ST tires.

Non-RV Portable Generator Installation

I have a 25-foot Surveyor travel trailer I also purchased a 3000-watt portable generator. Where would you recommend I mount this generator? On the tongue or on the rear bumper? It weighs about 145 pounds.
Leroy, (Los Angeles, CA)

Personally Leroy, I do not recommend permanently installing portable, non-RV generators. Besides, a portable generator should remain portable. They simply are not suited for a permanent installation in an RV. Certainly do not mount any generator at or near the LP cylinders. The best place for an RV-approved generator is mounted into the side of the coach within a correctly constructed generator compartment. Wish I had better news for you, but electrical integrity and safety are paramount when it comes to generator installations. Installations must comply with the NFPA 1192 RV Standards as well as the NEC.

George Bunzer - Gone, but Not Forgotten

George was a unique character. He was also my Dad. He was almost eighty when he died in March of 2002 and if it wasn’t for him, you wouldn’t be reading this, nor would I have a career in RV technical education. He passed down to me much of what he had absorbed through his mobile home industry genes, along with his sense of humor, his view of the world and his fascination with words.

George was a brilliant entrepreneur even before many really understood the meaningful depth of that popular moniker. A self-made man, he revolutionized the mobile home industry in Florida by being one of the first to build strictly custom-made, one-off, modular units, including a two-story mobile home. He employed a cadre of brilliant craftsmen within his business, Geo. J. Bunzer Industries, Inc. I grew up in that environment, spending my summers working for Bunzer Industries while going to junior and senior high school. Himself a gifted craftsman, little did I know that he was exposing me to some of the best craftsmanship in the building trades as well as instilling in me a true, hard-nosed work ethic. During one summer, I’d shadow a master carpenter, the next I’d be connected at the hip to a master plumber, then a master electrician, then a master troubleshooter, then a senior manager, etc., until upon graduation from high school I was well-versed in all the building and repair trades.

After college, marriage, military and another year under his tutelage, my wife and I relocated to Southern California where I began my independent working life at a facility that serviced both mobile homes and recreation vehicles. Through my college studies, as well as my years spent as a US Navy Seabee Military Instructor, and after a few years of master level troubleshooting and repair in various RV shops, I came to embrace the prospect of teaching and began my technical consulting career solely within the RV Industry. But that’s only half the story.

You see George was also a personality of sorts; he wrote many articles along with a monthly mobile home repair column for a small regional publication in Florida. In addition, after relocating to the mountains of Western North Carolina, he ventured into the radio host chair of a local AM radio station with his own, Ask George, daily broadcast featuring repair tips for home owners.

And oh how he loved those Carolina Mountains! Earlier, while still living and working in Florida, we’d visit those mountains every summer for a couple of weeks at an old, revamped, TVA housing project-turned summer vacation resort near Murphy, NC; right in the corner where NC, TN and GA all come together. We rented the same cabin every year so he could have the same convergent view of Hiawassee Lake and the mountains from the same worn sofa in the main room.

Well, after he retired from the mobile home business, George moved with Mom to those mountains permanently. He still wrote his George Sez column every month for that little regional in Florida, but he was also getting a lot of RV-related questions coming in. As I was now firmly entrenched in the RV Industry, working for a rolling stock RV dealership in San Diego, he'd forward those types of questions to me. I’d write the response and he’d publish the Q&A in his column. Eventually, the majority of the questions became RV-related so he suggested to the publisher that I take over the column. And the published, Gary Sez column was born. The year was 1976.

Soon thereafter, we all settled in the Murphy area to enter into a business venture that expanded on yet another of George’s ingenious inventions; the RV Chalet, (he held numerous other patents as well). Though that joint quest lasted only a year, it was successful, once again, in making an impact on the housing industry; the RV Chalet was featured in many articles and books showcasing unique single-family dwellings. (For a detailed explanation about the RV Chalet, go to this page).

In the meantime, back in California, I realized that the Gary Sez column was only featured in that one tiny tabloid publication in Florida. I wondered if it might garner interest in other RV friendly areas as well. This was before the days of media consolidation, when individual publishers still owned their respective geographical magazines. So the Gary Sez column gained additional traction. Within a few months one publisher wondered if he could change the name of the column to RV Doctor. I concurred as yet more publications signed on to the self-published labor of love. The RV Doctor column has now been published somewhere every month for over thirty-three consecutive years. And I have George to thank for that, among other things.

George lived the rest of his life in his beloved NC mountains. He wasn't afraid of dying, but he did have three wishes; he wanted to die at home, without pain, and with his family around him. He was granted all three wishes.

Shortly after he died, I was moved to write a song about him, basically thanking him for all the things he passed down to me over the years. So I gathered some of my musical friends and we booked time at a local recording studio in San Diego. I hope you enjoy this tune about the Old Man From the Hills, my Dad, George Bunzer.

Old Man From the Hills - Song

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No Output - RV Generator

I have a Generac gasoline generator in my motorhome. I started it up and it was running fine for about five minutes. Then it stopped putting out any electricity, but the engine is running fine. The 20-amp circuit breaker on the unit had tripped. I reset it and still no output. I have checked both circuit breakers with an ohm meter and I show resistance in the closed position and none in the open position. I checked all the breakers in the coach and they seem fine. Could the problem be further down the line? What is a "J-Box?” Any idea what else I should check? Karle, (Littleton, NC)

Karle, if you are sure the circuit breakers are okay, then there might be something more serious to contend with internal to the generator. First, with the generator running, check for AC voltage at the input to the circuit breakers. This will rule out the breakers and anything downstream. If there is no voltage or lower than normal voltage going into the circuit breakers, then the problem is likely a bad voltage regulator, rotor, or stator on the generator itself. All of these components are very expensive and difficult to replace and they mandate you take the coach to a qualified Generac dealer or service center for repair. 

Also check the voltage at the output of the circuit breaker. If there is voltage at the input to the breaker but not the output, then the breaker is faulty, even though it passed your continuity test. It may break down under current flow and/or higher temperatures. The J-box you referred to is the junction box. It is located fairly close the generator and is the transition connection between the flexible cable coming out of the generator and the conduit going into the coach. If AC voltage is present at the output of the breakers the next place to check is inside the junction box. Remove the cover and inspect and probe the wiring. If there is power there then the problem is further downstream of that. You did not mention whether you have to manually plug your shore power cable into a generator receptacle or whether you have an automatic transfer switch. If you have a transfer switch, that is likely to be the problem if the rest of the areas check out as good.

RV Travel Trailer Tongue Weight

We have a 1996 1/2-ton Chevrolet truck with a 5.7 liter engine and a 3.73 axle ratio. Our owner's manual says we can safely tow 7,500 pounds. We are now towing a 1997 Wilderness travel trailer, (no slideout), and are having no problems whatsoever with towing. Our ride is smooth and we never feel a big strain on the engine. We are thinking about selling our trailer and getting a new Wilderness with a slideout. The UVW on this trailer is about 6,400 pounds, but the hitch weight is substantially higher than with our current trailer. My question is, how important is hitch weight and what happens if your hitch weight is too much for your tow vehicle? I have heard from other RVers that if the hitch weight is too high, your front wheels on your tow vehicle may come off the ground at times and it will be hard/unsafe to drive. What are your opinions on this?
Ellen, (Butler, MD)

Ellen, knowing the correct hitch weight, or "tongue weight" as it is sometimes called, is crucial in order to establish a safe towing configuration with any conventional travel trailer. More prevalent in years past, inadequate tongue or hitch weight was a significant contributor to trailer sway. With today’s engineering standards being more defined, this probable cause from the past has been lessened quite a bit.

Still, in terms of most hitches, the ideal tongue weight should be about 12% of the total weight of the fully loaded trailer. Some of the larger trailers may have tongue weights nearing 17% of the total. Anything less than 12% could have a tendency to be the cause of trailer sway.

If the tongue weight is extremely heavy, such as your fear, the majority of stowed objects may need to be positioned aft of the axles rather than in front of them. In any case, it will be necessary to have your towing configuration properly weighed on a platform scale to determine the optimum positioning of all the stowed gear. All this assumes you are using a weight distributing hitch, by far the most common type of hitch today. As a point of reference, refer to this weight capacity chart:

Class Type Capacity

I Weight Carrying 2,000 GVW

II Weight Carrying 3,500 GVW

II (torsional) Weight Distributing 3,500 GVW

III Weight Carrying 5,000 GVW

III Weight Distributing 10,000 GVW

IV Weight Distributing 10,000 GVW

V Weight Distributing 15,000 GVW

Always mounted to the frame of the tow vehicle, this type of hitch, by its design, distributes the weight to both axles of the tow vehicle. Weight distributing hitches are the preferred method of towing all but the lightest forms of travel trailers. The weight distributing hitch works in concert with tongue weight and all but eliminates your concern of putting too much weight on the rear of the truck. A properly adjusted set of spring bars, in conjunction with a properly sized weight distributing hitch, will shift a portion of the tongue weight to the front axle of the tow vehicle. Your front tires will never leave the ground!

No More PB

I have a fresh water plumbing question. Our motorhome has the grey piping throughout. Recently we replaced the kitchen sink. When I went to Home Depot I was given the newer white type PEX pipe. I already have the crimper and crimp rings. As I made the repair I noticed the new brass fittings were snug in the white pipe but loose in the grey pipe. Continuing with the repair all fittings were crimped. When the water was turned on the grey crimps all leaked. It appears the grey piping is a slight bit larger on the inside. Is the grey piping becoming obsolete? Are there fittings that will convert the grey to the white? Camping World and most places are only carrying the white pipe. Where is the best place to find the grey pipe? Help! Denney, (Lehigh Acres, FL)

Denney, indeed, the older, gray, polybutylene water tubing is no longer available. The white tubing is called cross-linked polyethylene (PEX) and has a different diameter than the older PB. Thankfully there are “transitional” fittings available that will successfully mate the two types of piping together. One company producing them is called Flair-It. They are available at many online retail outlets, as well as most RV accessory stores.