RV Hydronic heating systems are very popular in upper-scale Class A motorhomes. A hydronic heating system uses a diesel, propane, or gas burner and an electric heating element to heat a boiler, which then circulates boiler antifreeze through various zones in the coach via small heat exchangers to provide heat. Hydronic heating systems also provide hot water for kitchen, bathroom, and shower needs.
Aqua-Hot
In August 2025, I completed service training on Aqua-Hot products as part of my requirements to become an RVIA Master Certified Technician.
The most prevalent hydronic system used in RVs is made by Aqua-Hot Heating Systems, formerly known as Vehicle Systems, Inc. In 2019, Aqua-Hot became part of the Airxcel family of brands.
Oasis by ITR
Another manufacturer of hydronic systems is Oasis by International Thermal Research (ITR), which is installed in Newmar motorhomes.
Of all hydronic systems, I have found the Oasis system to have the best troubleshooting and phone support among hydronic heater manufacturers. I prefer the Oasis’s low-pressure fuel implementation over the AquaHot units’ high-pressure fuel system.
Truma Combi
In November 2024, I completed service training on Truma products as part of my requirements to become an RVIA Master Certified Technician.
Truma Combi is used on smaller coaches such as Class C and Class B. It comes in multiple configurations and can run on Propane or diesel, and Plus models add a 1,700-watt (5,800 BTU/h) electric heating element that requires a shore power connection.
Propane Models (Eco vs. Comfort)
Truma Combi Eco / Eco Plus: Features two primary gas operating levels delivering 7,500 BTU/h and 14,300 BTU/h.
- Truma Combi Comfort / Comfort Plus: Upgrades the upper heating thresholds to include three operating steps: 7,500 BTU/h, 14,300 BTU/h, and a maximum output of 20,400 BTU/h.
- Truma Combi G Comfort: A specialized LP gas variant with five progressive stages, from 6,800 BTU/h to 20,470 BTU/h. [1, 2, 3, 4, 5]
Diesel Models (D Series)
- Truma Combi D Comfort / D Comfort Plus: Features up to six micro-managed burner levels designed to match heating demands efficiently, outputting between 3,400 BTU/h at its lowest up to 20,470 BTU/h on high. [1]
Elwell / Timberline
The Newmar Freedom Aire that I purchased in the Spring of 2026 has an Elwell / Timberline 2 hydronic system. I have experienced several issues with this hydronic system in my coach. Elwell does not provide technician training, unlike other hydronic heater manufacturers. Instead, they work with RV manufacturers and service departments. After the warranty expires, you must take your coach to a dealership for service. Technical service information focuses on visual presentation rather than diagrams and true troubleshooting guidance. Elwell’s support answers questions but lacks the details needed to understand system issues or resolve them.
Annual Service
Aqua-Hot and Oasis RV Hydronic manufacturers recommend an annual service schedule, regardless of the system’s usage throughout the year. If issues arise with the hydronic heat system, perform annual service first.
Diesel Class A at Auction – Google
Wayne ways excellent and detailed with his inspection. He called me to ensure he knew what my priorities were for inspection and continued to update me throughout the process offering valuable insight and recommendations. Would highly recommend him to any of my friends and family if needing an inspection of RV.
Lichtsinn RV in Forest City, IA – Google
I chose Wayne Koster’s as my RV inspector for the Winnebago Navion I ordered from Lichtsinn RV in Forest City, IA. I had owned a couple other RV’s but this would be the 1st on my own. While I was purchasing a new vehicle, I was concerned because of all the difficulties the manufacturers were having getting parts, etc. Wayne tested every element of the unit and sent me a very detailed report. He really gave me the peace of mind that I was getting what I was paying for. Wayne is knowledgeable, courteous and has the innate ability to work well with the RV dealerships. I am grateful that I had Wayne on my “team” Janan Bartell, Ponte Vedra, Florida
Used Travel Trailer – Google
I had Wayne inspect a used travel trailer. Wayne was very professional and was able to inspect in a very short turnaround. Wayne provided me with a very detailed report that the dealer viewed and addressed during negotiations. I am very happy I had Wayne look for the issues so I could make an informed purchase.
Winnebago Motorhome – Google
In all aspects it was a delight to have Wayne provide me with inspection services in my considering the purchase of a motorhome. Response to my initial contact was prompt, courteous and professional. It was my intention to be absent from the inspection but circumstances made it possible to check the coach out while Wayne was just finishing. Again, with the utmost professionalism, Wayne stepped me through the items of concern he found. It is clear from his findings and from comments of witnesses that his inspection could not have been more thorough. This quality of service is well worth the cost.
Electrical Service – Google
Quick and competent service. Excellent website and payment interface.