Reduce motorhome weight, conserve water and propane, and enjoy hot water on demand.
By Gary Bunzer
RV owners share many common interests and concerns. Two major aspects of the lifestyle that all RVers should pay special attention to when on the road are weight and resource conservation. Carrying excess weight in a motorhome can lead to premature tire wear; undue stress on the drivetrain and brakes; and steering, towing, and handling issues. Likewise, conserving onboard water, battery power, and propane should 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 reduce weight, save water, use very little battery power, and consume less propane than a similar appliance. But that’s exactly what the RV-500 tankless water heater from Precision Temp accomplishes. I’d heard good things about the RV-500 for some time. I studied the specifications and read all the literature, but I had never had the opportunity to actually install a brand-new unit.
I was aware that the RV-500 was a logical replacement for any 10-gallon RV water heater, but I was surprised to learn that with only a slight modification to the height of the cutout size in the sidewall, it also can replace aging 6-gallon units. But why would someone want a tankless water heater?
Less weight is one of the major draws. The RV-500 weighs 35 pounds, which makes it slightly heavier than a 10-gallon Atwood heater but 10 to 20 pounds lighter than a comparable Suburban heater. The difference is that traditional water heaters are filled with water, which weighs approximately 8.35 pounds per gallon; the RV-500 is not. That means you can eliminate almost 80 pounds of travel weight when replacing a 10-gallon, direct-spark-ignition (DSI) Atwood heater and 90 pounds when replacing a like-size Suburban water heater.
Another benefit is that a tankless water heater can supply an unlimited amount of hot water upon demand. As long as there is a supply of fresh water and propane available (along with 12-volt-DC power) to the RV-500, it can produce endless hot water for your motorhome’s shower and sink faucets.
For those unfamiliar with how a tankless water heater operates, here’s a brief explanation. First, as the name suggests, there’s no tank. There also is no pilot flame, since the RV-500 is a DSI appliance. The high-performance, 12-orifice burner ignites only when water flows. When the unit is powered by 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 motorhome.
Once water begins to flow (delivered by city pressure or onboard pump pressure), a small rotary flow meter is activated and begins to monitor the flow of the cold water entering the RV-500. Once the meter senses a steady flow approaching 1/2-gallon per minute, a signal is sent to a modulating LP-gas valve, opening the valve and activating the automatic spark igniter. As with most other DSI appliances found on RVs, the control board opens the gas valve, creates the spark that ignites the incoming fuel, and monitors the flame to ensure the propane is indeed being consumed at the burner.
The microprocessor constantly calculates the amount of water flow as well as the temperature of the water at several locations within the heater and adjusts the propane flow through the gas valve accordingly. This modulating of propane inside the gas control valve makes for a very efficient propane-burning appliance. It consumes only what it needs in order to maintain a preset water temperature.
As the water enters the system and passes through the heat exchanger on its way to your shower or sink, the temperature is monitored by thermistors positioned at the cold inlet, within the heat exchanger, and at the hot outlet. The processor interprets this information and recalculates the amount of propane flow needed to maintain a consistent output water temperature within 2 degrees Fahrenheit of the preset temperature. Even though the thermostat is preset at the factory to approximately 120 degrees, it is adjustable to any point between 90 and 135 degrees. However, company literature notes that adjusting the temperature is not recommended, since injuries could occur. As long as a hot faucet is open, hot water will continue to flow. The burner shuts down when water flow stops. What this means is that you never have to worry about running out of hot water just before you rinse the shampoo from your hair.
Propane appliance safety is always a concern in a motorhome. The RV-500 is equipped with multiple safety features, including two electronically operated over-temperature sensors that will shut down the sequence if exceeded, as well as a thermal energy cutoff (ECO) switch that’s automatically resettable.
A redundant solenoid controls gas flow. The gas valve closes in less than 1 second if no flame is sensed upon initial ignition of each sequence. The circuit board will make two attempts to light the burner and then go into lockout. A lockout condition means something is amiss — low or no propane pressure, insufficient voltage, etc.
There is a typical pressure-and-temperature relief valve (P&T) common to all water heaters. Like standard RV water heaters, all combustion takes place outside of the living area, 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 that another fuse be installed 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 pulls out from the exterior for maintenance and inspection. According to the installation and operating instructions that are included with each heater, the RV-500 should undergo a routine inspection by a qualified service technician at least once a year. The guide includes eight areas of concern that should be looked at during the inspection.
Replacing an existing tank-type RV water heater is not particularly complicated. After draining the existing tank, disconnect, protect, and move aside the 12-volt-DC wires, hot and cold water lines, and the propane copper tubing. Next, remove the water heater. The RV-500, which measures 13.5 inches wide, 13.5 inches deep, and 14.5 inches high, should slip right into the same hole as the current 10-gallon heater, although it may be necessary to reroute the propane tubing. 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-DC wires and the hot and cold water lines attach at the rear of the RV-500. The only wiring modification may be to reroute the hot wire from the existing master switch or to run a new conductor from a newly installed switch, plus the negative ground wire.
If you’re replacing an existing non-wired, pilot-type water heater, be sure to use at least 18-gauge wiring for the hot and ground circuits (I recommend 14-gauge wiring). Protect the switch and power circuit with a 3-amp to 5-amp fuse or circuit breaker.
One difference with the water tubing connections on the RV-500 is that the hot and cold are reversed. 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 find out soon enough. You should not have that problem, however, since both water connections are clearly labeled. Any RV handyperson should be able to replace a standard tank-type water heater with the RV-500.
Technical specifications, installation manuals, users guides, etc. are shipped with each unit and also are available at the company’s Web site (www.precisiontemp.com). These documents cover the full spectrum of installation options as well as all the nuances of safety. Read all the paperwork prior to installing and using the RV-500. As with any propane-powered appliance, check all connections for leaks prior to putting the appliance into service.
I recommend that the motorhome’s entire propane system, not just the connection at the heater, be leak-checked. Have a certified RV technician perform a timed pressure drop test. In addition, this appliance, like all RV appliances, must be fed a steady diet of propane delivered at 11.0 water column inches. A manometer and a specific set of procedures are necessary to set the propane delivery pressure and to test the system for leaks. Rely only on a certified or master certified technician to perform these procedures.
RVers everywhere have embraced the practicality of sustainable living. That’s exactly what self-contained RVing is about, right? Without doubt, the tankless, on-demand water heater is here to stay and is likely to become increasingly prevalent as more suppliers offer these appliances. As a growing number of RV manufacturers become more weight-conscious, and with 8 million (maybe more) RVs on the road in America, I believe Precision Temp just may be busier than ever.
The RV-500 has been on the market since 1996 and was replaced in 2013 by the RV-550 and RV-550-NSP. The RV-550 is the highest-output water heater on the market and installs and functions in the same way as the RV-500. It incorporates a new modulating gas valve system that controls water temperature while eliminating some of the electronics, which increases reliability and also simplifies servicing the unit.
Wind protection and cold weather protection, optional on the RV-500, are now standard in the 550 Series. When the temperature approaches freezing, the cold protection turns on automatically and protects the unit from freezing down to -20 degrees Fahrenheit. (Note: the propane and 12-volt power should be left on to assure freeze protection.)
The RV-550-NSP (No Sidewall Penetration) is the first water heater in the industry designed to mount in the “basement” or storage area. Its flue consists of a 2-inch exhaust pipe that extends through the floor, just like a generator exhaust pipe. This allows for a cleaner exterior sidewall, which is especially important where graphics are involved. Plus, it opens up floor plan options for RV manufacturers and increases storage options.
Both of the PrecisionTemp RV-550 models have a suggested retail price of $1,125, which includes the door, cold weather protection and wind protection, and installation fittings. For more information about PrecisionTemp’s products, visit www.precisiontemp.com or call (800) 934-9690. And remember: RVing is more than a hobby; it’s a lifestyle!