Imagine this: You wake up in the morning to the sounds of nature. Somewhere, Norwegian Composer Edvard Grieg’s iconic classical piece Peer Gynt Suite Number 1, Opus 46 “Morning Mood” is softly playing. The smell of coffee and breakfast warmly greet you to this new day. Ah, the joys of the RV Lifestyle. You hop into the shower, and then- YOUR JARRED AWAKE because you’re out of hot water.
Before now, Hydronic heating systems for RVs came with luxury-level Class A motorhomes only. They’re now the new standard for diesel motorhomes for the 2022 model year. We’ll show you if hydronic heating systems are worth it. You’ll learn how they work, their limitations, and what we found to be the best hydronic water heaters on the market.
What is RV Hydronic Heating?
If you look through the annuls of RV History, you’ll see that today’s innovations come from previous era technologies. The most straightforward example is the rooftop or hatch tents that attach to SUVs. During the Antique Era (1910-1944), the Auto Camp was a wood platform connected to a Ford Model T’s running boards and had a canvas tent attached to the car’s roof.
Hydronic heating systems work like commercial or residential boiler systems. Instead of water, the system uses 50/50 propylene glycol antifreeze (a.k.a. non-toxic antifreeze). This type of antifreeze is the same version you use for your radiator and your pipes when you winterize your RV. If the system ever runs low, you can pick up a bottle at your favorite camping store, big-box superstore, or online.
What Are the Benefits of Hydronic Heating?
Using a hydronic heater in your RV combines three critical components in your diesel motorhome, eliminates the need for propane, and evenly distributes heat throughout the interior, including the storage basement.
- Interior Heating
Instead of using HVAC ductwork in the subfloor, the RV’s heat registers have substation exchanger boxes representing a zone. Small tubing runs from the primary hydronic device through each of the zone substations. The heated antifreeze flows through the zones on a continuous loop. When a substation senses a temperature lower than the desired setting, a quiet fan starts moving air over the tube, taking advantage of the radiant heat.
By the end of the loop, the primary system reheats the antifreeze and continues the process. Forced air systems push air to the point where it will find ways to leak out through your weatherstripping. Hydronic heating systems circulate air which minimizes the “pushing effect.”
- Engine Block Warming
Late season, cold weather camping, or winter camping in the Snowbelt States can be problematic for diesel engines. Diesel fuel has elements in it that become gel-like around 40°F, and it freezes at 32°F. That’s why it’s imperative to have a diesel engine heater. Routing the tubing from an RV hydronic heater to your RV’s engine accomplishes the same goal.
- Endless Hot Water
If you walk around a new diesel motorhome, a red flag may pop up in your mind, but it might not be immediately apparent. Your mind is trying to tell you that the motorcoach is missing a water heater. Before you get frustrated or walk away, the motorhome does have a water heater; it’s now a part of the hydronic heating system.
The boiler inside the heating system has a water line wrapped around it. Whether the water comes from your freshwater tank or your city water connection, you now have a tankless water heater with on-demand hot water. Say goodbye to those quickie 2-minute scrub downs and hello to a relaxing shower. Remember, your grey water tank holds only so much.
How Does Hydronic Heating Systems Heat Up?
RV hydronic systems, like the Aqua-Hot by Airxcel, takes advantage of every heat source possible. The Aqua-Hot is the most popular within the RV Industry, but there are other brands. Generally, they work the same way. Heating works in two ways; either the source maintains the temperature or brings the cold unit up to temperature.
When you’re at your campsite, the system will use the incoming electricity to maintain your desired heat setting. The smaller Aqua-Hot 450D has one electric heating element, and the larger 600 series has two. The electronic heating elements maintain water temperatures as long as the unit doesn’t have to work too hard to stay at temperature.
While you’re driving, hydronic heating systems use engine heat to maintain temperatures as long as the tubing runs to the motor. It’s a great way to keep your hot water at temperature and keep the coach warm, so the dashboard heater doesn’t get overwhelmed.
The last way is the diesel fuel burner. Like your gas generator, built-in hydronic heating systems feed on your RV’s fuel tank. The burner only ignites when the unit needs a significant warm-up and is very fuel-efficient. Once the unit is at the desired temperature, the fuel burner shuts off and relies on the electric or main engine to maintain the heat.
Are Diesel Heaters Safe?
Diesel hydronic heaters are safe to use during regular operation. Most of the time, you’ll power up the device with the toggle switches on your control center panel and forget the device is even there. If there is a problem, the bay that houses the hydronic heating system has a panel with indicator lights. If something’s wrong, the rows of green will be interrupted by a red light that points out the problem.
Experts that work these systems always recommend that you drain the antifreeze before you begin your hydronic heater troubleshooting. You can seal off the closed-loop tubing, so you’re only emptying the primary unit. Use an extra-large container and PEX pipe that can handle the high temperature, so when you’ve completed your work, you can pump the antifreeze back in, saving money and the environment.
Maintaining Your Hydronic Heating System
Adding your hydronic system to your annual RV preventive maintenance checklist is an excellent way to increase longevity. Your inspection should include checking the integrity of hoses, connections, pumps, and wiring. The boiler comes from decades’ long technology. Residential hydronic boilers last between 10 to 20 years, and there isn’t any data that says your RV version is any different. Make sure you check your antifreeze levels monthly.
If you need to manipulate any of the hoses, boiler, or components, wear protective gloves—internal temperatures average 190°F. Some companies sell products with everything you need to conduct your annual maintenance on your RV’s hydronic heater.
For example, ITR Oasis sells an annual maintenance kit that replaces the various filters, ignitor, and fuel nozzle stone. The hoses used are PEX pipe and other standard insulated rubber piping used in plumbing. Fittings, clamps, and electronic components are common pieces found at any hardware store.
Efficiency and Capabilities
Systems in diesel Class A RVs are energy efficient. In a hypothetical situation where the fuel burner runs consistently, one gallon of diesel would run the burner for eight hours. Remember, hydronic heaters use electronic elements and the main engine’s heat to maintain the antifreeze’s temperature.
For those that have had the “privilege” of experiencing heating from older boiler systems, you wore summer apparel, had box fans in the windows, and it took days for the temperature to adjust every time the maintenance staff made any adjustment. Yet, the outdoor thermometer read winter temperatures as low as -15°F.
The good news is, diesel hydronic heating systems aren’t like “Old Bessie” from that previous experience. You can adjust the temperature up or down accordingly. When it comes to hot water temperature, you and your family may have to settle on a compromised setting.
Suppose someone likes to take showers as if they’re a lobster in boiling water, and the other prefers a soothing warm shower that makes them feel like melted butter. A high setting will give the lobster person their desired temperature, but finding the desired warm temperature without losing water pressure, might be a problem for the melted butter person. The temperature range can be narrow with hydronic systems, so finding the perfect setting is a challenge.
Campervan Hydronic Heating Systems
When we used the term “diesel motorhome” throughout our discussion (except the first time), did you only think of Class A RVs? We purposefully generalized the phrase for a reason. Hydronic heating technology dates back to 1984. Various companies have miniaturized these systems throughout their evolution to make them cost-effective for the European Campervan Industry.
As the North American Class B Campervan Sector continues to catch up to the seasoned veterans of European campervan builders like Groupe Rapido (and we’re pretty much there),
Best RV Hydronic Heating Systems
Aqua-Hot Heating Systems started in 1984 by Harold “Hap” Enander. He designed the system because he couldn’t find an RV furnace or water heater that fulfilled his high standards. His system sold well in other industries. In 2019, Aqua-Hot joined the Airxcel Family. With Airxcel’s resources, Aqua-Hot joined its air conditioner counterpart, Coleman Mach, becoming the leader in RV hydronic heating.
Aqua-Hot has eight different models that range in size and BTU capability. The 250P and 400P use propane to fuel the burner instead of diesel. When you perform your annual maintenance, you can purchase an Annual Service Kit from the company directly. It comes in pink or green based on the color of antifreeze used in your system.
The Alde Heating System is new to the North American RV industry, but the Swedish company has been in business for over 70 years. You can find their radiator hydronic heating system on the nuCamp Cirrus truck camper. Unlike the Aqua-Hot and other brands, the Alde uses radiator fins that operate the same way as that “old school” version you had growing up.
The Alde system uses both electricity and propane as an environmentally friendly fuel source. The radiator fins create self-convection, making the warm air rise to start a circulating motion. You don’t have to worry about zone fans breaking or other issues.
International Thermal Research (ITR) opened its doors in 1984. It specializes in the research and development of diesel and non-powered burner systems. You’ll see their products in the U.S. Army, arctic, marine, and RV applications. The Oasis product line is exclusively for the RV market and currently has five different models. The design, manufacturing, and testing in ITR’s British Columbia, Canada’s facility.
The new Oasis NE puts out 50,000 BTU of heat and 85,000 BTU for the Oasis NE-S. All five models can be single or dual looped with five zones. You can mix and match between three different zone devices to suit your needs. You may want your rear bathroom to have in-floor heating, your master bedroom could have passive radiator heating, and the living room may be the best place for convective air vent heating to circulate the air.
Can Gassers or Towables Use a Hydronic Heater System?
Unfortunately, hydronic systems work on either diesel, electricity, or propane. Diesel has a low ignition point like propane. RV manufacturers could install one of these units in gas motorhomes or travel trailers, but the prices of these units and the peripheral parts can exceed $5,000. Conventional six-gallon or ten-gallon water heaters with various plumbing and electrical can stay below $1,000 per RV.
If you want to retrofit a hydronic heater into your RV, be prepared for a lot of work. A DIY project like this requires disassembling cabinets, your floor, and your entire heat ducting network to install everything. In this article from Trailer Life, you’ll see someone who used to work for one of the hydronic heating companies install a system in his Grand Design Imagine travel trailer.
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How Does a Hydronic Heater Compare to a Tankless or Conventional System?
For the next few years, RV furnaces, conventional tank water heaters, and tankless water heaters aren’t going anywhere. These devices are still cost-effective, reach desired temperatures quickly, and a traditional forced-air RV furnace will heat the interior quicker than hydronic systems.
To learn more, we have an article about How to Convert Your RV Propane Water Heater to Electric to make it more energy-efficient. If you’re looking to change out your water heater for a tankless version, you can see our recommendations on the Best RV Tankless Water Heaters we discovered after extensive research.
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