Aqua-Hot 250P: RV Heating and Hot Water

John Carrillo with an Aqua-Hot 250P cutaway and components.
John Carrillo with an Aqua-Hot 250P cutaway and components.
Photos by Shawn Spence

Travel trailer and fifth-wheel owners can tap into continuous hot water and quiet, even heating with the new Aqua-Hot 250P

The smiles you see on the faces of families coming out of those big diesel motorhomes on cool autumn mornings in the campground have a lot to do with the good night’s rest and hot showers everyone enjoyed.

Long a staple in half-million-dollar-and-up mobile residences, hydronic heating systems now are available for all RVers. Hydronic systems supply an unlimited amount of hot water and quiet, evenly distributed moist-air heating throughout the interior.

Throughout its history, beginning in 1984, Aqua-Hot has focused on making heating units for the motorhome market. The good news for owners of travel trailers and fifth-wheels is that Aqua-Hot recently introduced a smaller LP-gas- and electric-powered system that can be installed in towable RVs.

Hydronic systems work much like radiant heaters in cars. An antifreeze-based fluid circulates through the system and maintains a temperature of 190 degrees Fahrenheit for heating. When warmth is needed, up to five heat exchangers come on to deliver a moist, even heat without drying the air. For domestic hot water, water flows through the boiler unit and maintains a 120-degree temperature.

John Carrillo spent nine years at Aqua-Hot as a production worker, service technician and technical adviser before leaving in 2008 to start Heat My RV and do business as an independent hydronic-heating specialist. With his office located across from Aqua-Hot’s headquarters in Frederick, Colorado, Carrillo has been a go-to guy for Aqua-Hot repairs and installations. An RVer himself, Carrillo travels to Arizona and California in January and February to service RV heating systems at events and rallies, including the giant Quartzsite, Arizona, show.

When Carrillo offered to give us an inside look at the installation of the new Aqua-Hot 250P in his Grand Design Imagine travel trailer, we took him up on it.

How It Works Interior Heating: Specially formulated antifreeze is heated by the burner in the main heating unit (left). A circulation pump pushes the hot antifreeze to each heat exchanger using a closed-loop system of tubing. When a zone calls for heat, the exchanger fan comes on, pushing hot air. Cooled antifreeze returns to the burner plenum for reheating. HOT WATER: In the hot-water system (right), potable water is heated through an isolated loop, requiring no tank. The water runs through the coil where it is heated and flows, on demand, to the RV’s faucets.
How It Works
INTERIOR HEATING: Specially formulated antifreeze is heated by the burner in the main heating unit (left). A circulation pump pushes the hot antifreeze to each heat exchanger using a closed-loop system of tubing. When a zone calls for heat, the exchanger fan comes on, pushing hot air. Cooled antifreeze returns to the burner plenum for reheating.
HOT WATER: In the hot-water system (right), potable water is heated through an isolated loop, requiring no tank. The water runs through the coil where it is heated and flows, on demand, to the RV’s faucets. Illustration by Rob Roy

PREPARATION AND INSTALLATION

For the installation, the drawers and cabinet facing covering the Imagine’s original forced-air furnace were pulled out. From there, the original LP-gas furnace was quickly removed.
The 250P measures about 12 by 13 by 22 inches and weighs 84 pounds. Surprisingly, it fit perfectly where the old furnace sat. There are many options concerning where to place the unit, including the front storage compartment, but with cargo space always at a premium, using the old furnace bay was a no-brainer.

Once the hole in the flooring of the trailer for the unit’s exhaust manifold was cut, the technician spliced into the potable water lines and connected them to the new system, which are on top for ease of installation. A reservoir mounted on the wall above the system will make it easy to top off the heating system antifreeze fluid through the exterior-access panel. An exhaust pipe was dropped down with an elbow, sending the heat from the unit out the side. Because the system runs on propane or electricity, no smell or smoke is discharged.

The most labor-intensive part of the installation required dropping the underpinning beneath the trailer to run the plastic piping for the antifreeze and electrical wiring to operate the heat exchangers. Runs were made to each of the five heat exchangers, which consist of a combination of the two-fan, 8,200-Btu Cozy units and the smaller single-fan, 4,000-Btu Whisper units.

At the rear of the trailer, the existing water heater was pulled out, and one of the heat exchangers was mounted in its place. That left additional storage space, and Carrillo plans to have a detachable door fabricated to cover the opening.

After mounting the heat exchanger in the water-heater opening, a vent passage to heat the primary living space was cut. Additional exchangers were placed beneath the kitchen island, in the primary living area, and inside the bathroom to heat it and the bedroom. One heat exchanger was mounted in the front storage bay to keep it and the entry point for the water systems warm. A direct connection was established from the heat exchangers to the vents, plus the existing ductwork, to move heat throughout the trailer.

After the plastic pipe and heat connections were made, 6 gallons of propylene-glycol antifreeze solution were used to fill the system. Aqua-Hot recommends making a 50-50 mix, which can change depending on the brand of antifreeze used. The connection for the electrical element was then completed. The LP-gas and electric-element switches were mounted next to the existing thermostat using the wires from the original switches.
The furnace wires were connected to the LP-gas switch and the water-heater wires to the electric-element switch.

OPERATION AND EVALUATION

As the Aqua-Hot 250P went to work, the antifreeze mixture got up to its 190-degree Fahrenheit target within 10 minutes, before shutting down the LP-gas connection and using the electric element to maintain temperature. For daily dish- and handwashing, the electric element will be up to the job, requiring use of LP-gas only when taking showers or other high-use hot-water tasks.

The 250P was, in fact, whisper quiet, sounding similar to a white-noise unit. Once the cabinets in the bedroom are reinstalled, the noise will likely be barely perceptible. Hot water left running for more than 10 minutes had no drop in temperature. Little noise was apparent, but you could feel hot air by placing your hands or feet near the heat registers.
Aqua-Hot tests show a usage of .7 gallons of LP-gas per hour when in constant use, compared to approximately .5 gallons per hour when the stock furnace (40,000-Btu) and water heater (10-gallon/10,000-Btu) were in operation. That said, having the burner run continuously is uncommon, as it engages only until the internal temperature reaches roughly 190 degrees, then shuts off, according to the company.

Harold Odgen, Aqua-Hot’s director of sales and marketing, says the retail price for the 250P is $3,887, plus the heat exchangers, plastic tubing and accessories, which add from $1,000 to $1,500 to the installation cost.

Labor can range from $1,000 to $5,000, according to Carrillo, with the final cost being determined by the length of the trailer or fifth-wheel and number of heat exchangers required. Owners will be encouraged to send photos and any wiring diagrams they have to determine the installation cost estimate. Aqua-Hot has more than 200 authorized service centers with more than 800 certified technicians.

Hydronic-Heating Advantages

Continuous, tankless hot water: In the Aqua-Hot 250P, water flows at 1.5 gallons per minute, with no recovery time.

Even heating: Multiple heat exchangers installed throughout the RV warm the air.
Quiet heating: The system is barely audible, without the noise of forced-air furnaces.
Fuel efficiency: The system burns LP-gas when 120-volt AC power is not available, and the electric element can be used when connected to shorepower.

Low emissions: LP-gas burns clean with no smoke or smell.

Virtually maintenance-free: All that’s required is checking the antifreeze level a couple of times a year, and removing and cleaning the flame detector with a Scotch-Brite pad. The company also recommends running the unit a minimum of once per month for optimal performance.

TECH TIP>> Winterizing the potable-water side of the Aqua-Hot system

Since there is no tank or bypass, winterizing your RV with the Aqua-Hot 250P is essential and easier than with a standard water heater. Do not use compressed air on any RV with a demand water heater. Drain the freshwater tank completely, then connect a pickup hose to the intake side of the demand water pump. Insert the end of the hose into a gallon of RV/marine potable antifreeze, turn on the pump and open every faucet in the RV one at a time until the antifreeze starts flowing. It will probably take at least a couple of gallons.
Make sure the antifreeze flows through both hot and cold lines, and that you get the washer and dryer hookups, outside shower and low-point drains flushed as well. There is no need to winterize or drain the antifreeze solution from the circulating system for the heat exchangers.

Aqua-Hot, www.aquahot.com


 

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