Quiet Heat, Continuous Water
All motorhomes can now be fitted with an Aqua-Hot hydronic system, which was formerly reserved for diesel pushers
Self-containment is the key to making an RV as livable as a home, and two of the most important elements in that regard are the water heater and furnace. Commonly, supplying hot water to the faucets and shower — and keeping the interior warm — has been relegated to independent components. Hot water usually comes from a 6- or 10-gallon gas or gas/electric appliance, and heat is provided by a forced-air furnace. But there are limitations to both.
Standard water heaters do the job with little complaint, but don’t plan on taking long showers. Most people find out the hard way that the hot-water stream is not unlimited — especially when trying to rinse shampoo out of long hair. Typical furnaces supply warm air, but most people experience large swings in room temperature between cycles, and in the middle of the night the fan and combustion chamber can sound like an airplane taking off from your patio.
For years, a number of Class A motorhome builders have circumvented the use of standard RV-issue hot-water tanks and furnaces with the use of hydronic water and comfort heating. Since these systems relied on diesel fuel to power the burner, they were reserved for diesel pushers, and usually only in the higher end of the market. Aqua-Hot is a major supplier of hydronic systems, and the introduction of its LP-gas/electric counterpart to the diesel models is changing the paradigm when it comes to heating and hot water.
Now that diesel fuel is out of the equation with the Aqua-Hot 400LP heating system, trailer and fifth-wheel builders are able to take advantage of hydronics. The benefits of using hydronic components are dramatic. On the heating side, the warm air is moist enough to eliminate the use of a humidifier, which prevents cabinetry and other wood items from drying out, and, of course, the same for our skin. And the big point: Temperature stability and the distribution of heated air are much more even.
The system has two pumps, which can circulate heat to eight registers, four in each of two zones, controlled by dedicated thermostats. This type of flexibility makes the distribution of heat extremely versatile and complete. For example, registers can be placed in the bedroom, bathroom and storage bay in a fifth-wheel. The other pump could service registers in the kitchen, living room and utility bay, and in places where the water manifold and water pump are located. The best news: It’s quiet. In fact, it’s so quiet that newbies will likely get out of bed in the middle of the night to make sure the warm air is actually flowing, although the fact that they are comfortable is all the confirmation they really need.
On the water side, a tankless system produces 90 gallons per hour of continuous hot water, on demand. Even those who lollygag in the shower will have a hard time running out of hot water.
The heart of the system is a metal box that measures 291/2 x 181/2 x 12 inches and houses a burner and an array of tubes and fittings, and weighs 184 pounds when the boiler tank is filled with a 50/50 mixture of propylene-glycol antifreeze and water (distilled, deionized or soft water is best). While the propylene-glycol-based antifreeze is safer than ethylene-glycol-based antifreeze used for automotive use, it’s not the same stuff used for winterizing RV water systems. RV antifreeze is not able to transfer enough heat and has no rust inhibitors. Therefore, boiler-type propylene-glycol-based antifreeze must be used for proper operation of the system.
Tied to the boiler unit is an electronic control panel installed in close proximity that keeps tabs on critical functions via status lights. The control panel performs electronic diagnostics in the event of a power deficiency or malfunction. An interior switch plate, mounted in a convenient location inside the RV, turns on the burner and controls the hot-water function. Continuous hot water can be supplied only when the burner is activated using LP-gas.
Unlike a typical RV furnace that forces heated air through a network of ducting, the Aqua-Hot 400LP utilizes individual heat exchangers that are strategically placed and plumbed, in series, via PEX tubing with a 5/8-inch outside diameter (OD). Fans in the heat exchangers run on 12-volt DC power.
So here’s what happens: The heat source is selected from the interior switch panel. Once the burner switch is on, the boiler tank heats the antifreeze and water to 190 degrees F. When one or both of the zone thermostats call for heat, the heated antifreeze and water flows from the tank to the heat exchangers where internal fans blow the heated air into the interior of the RV. The cooled antifreeze-and-water solution returns to the tank where it is reheated.
When a faucet is opened, the water is heated on demand and remains continuous until the aforementioned 90-gallons-per-hour flow is exhausted. Since it’s highly unlikely anyone will use up that much hot water in an hour, the supply effectively remains unlimited.
While the previously mentioned dimensions and weight suggest that the Aqua-Hot system will occupy a sizable amount of space, keep in mind that it replaces two fairly large components: the standard hot-water tank and the furnace. Beyond the swap for space, installation of the boiler requires a single-point location, and there are no vents required on the side walls of the RV. Unlike a standard water heater that uses a large (and not so pretty) access door on the exterior and, depending on the unit, intake and exhaust vents or a large panel for the furnace, the Aqua-Hot vents and exhausts through the bottom. Normally, a compartment door to the boiler and control panel is provided, but when closed there is no unsightly hardware to break up the exterior look.
To install the Aqua-Hot, the space must be designed so that a special mounting plate can be bolted to the framework. This plate accepts the boiler housing and an exhaust pipe that is routed to the outside, underneath the RV. As part of this requirement, the plate must be installed so that the underside is exposed to the outside. Therefore, when installing in a fifth-wheel or travel trailer, special consideration must be given so that the plate will not be covered by underbelly material.
Once the boiler housing is bolted in place, the PEX tubing, propane supply line and electrical wiring are connected. Access to the components in the boiler housing is provided by a panel that can be removed for service.
To get an idea of how an actual installation would work under real-world conditions, a 400LP system was integrated into a 2015 Forks Continental for our perusal. This is a luxury fifth-wheel, and heat distribution is critical when dealing with a 45-foot RV.
The designers and engineers decided on a two-zone system, controlling heat exchangers in the bedroom and bathroom with one thermostat and the galley and living room with the other. Heat exchangers were placed in cabinet structures at floor level in strategic locations with PEX tubing routed to each one.
Routing the PEX tubing is easier than working with traditional heat ducting, which is much larger and bulkier, because less space is required for runways. Heat exchangers were also installed in the main storage bay and utility center, to prevent freezing in cold weather. To achieve the same two-zone coverage with a standard RV furnace would require two systems, and that would suck up additional space for the installation and ducting.
Plumbing for the domestic hot-water system uses PEX tubing in sizes up to 5/8-inch OD, depending on the number of fixtures. There’s not much difference between hooking up a standard hot-water tank and the Aqua-Hot, except that there is no longer a need for a winterizing bypass valve on the back of the unit because the system is tankless.
Although the Aqua-Hot 400LP is a fairly complex assembly of components, regular maintenance of the system is not that complicated. It’s suggested that the system is run monthly to ensure proper operation of the burner. This requires running all the heat zones until warm air is blowing out of the heat exchangers.
The only other “watch” is to keep an eye on the level of antifreeze and water in the expansion tank. When filling, it’s important to release any air pockets, which is a simple procedure. The manual provides instructions for winterizing the system and getting it ready again for service when it warms up. A refractometer can be used to measure the proper amount of propylene glycol in the antifreeze solution.
Obviously, there is an upcharge for an Aqua-Hot system, but living with even, almost silent heat — and continuous hot water on demand — is pure bliss.
Aqua-Hot Heating Systems
800-685-4298 | www.aquahot.com