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Hydronic RV Heating Explained: Aqua-Hot, Hydro-Hot, and Oasis Systems

The addition of an Aqua-Hot or hydronic heating system to your RV is a valuable one. While they are usually factory additions, they usually cost around $10,000. These systems are used for heating air and water in the RV and can be a fantastic system… when they work. They also, however, are extremely complicated. I have a love-hate relationship with our hydronic system, so today, let’s learn about it!

This RV System Is the Best And Worst To Have At The Same Time - (Hydronic Heat)

What Is Hydronic Heating? 

Hydronic heating may be complex, but it’s fascinating how the whole process works. The system provides heat for air and hot water inside your RV, no matter where you are parked. Some even heat the engine or pull heat off the engine.

Hydronic systems are heaters that heat up a special antifreeze solution to circulate heat into the coach. Think of it like a heat battery, usually diesel, propane or electricity heats up a fluid that is used to heat other things. This heat is stored inside a tank and can be used later or immediately. Some systems can heat with multiple heat sources all at the same time or move heat in two directions. For example our system can heat the engine (when its cold) or pull heat off the engine (when its hot). This allows us to use heat from the engine to warm the inside of the vehicle or heat our water. Cool Right!

How Does a Hydronic RV Heating System Work? 

The hydronic RV heating system transfers heat from various energy sources into a liquid antifreeze solution. (The antifreeze is a solution that wont freeze if the coach is not being used and prevents corrosion in the system)

Frequently, the heat sources are electric elements or a diesel boiler, but sometimes, they can also be propane. The hot liquid flows through system loops within the RV that pass a series of vents inside. 

hydronic RV heating System Vent
Air heat exchangers are usually located near the floor of the RV and will have a small fan that blows air through them. They are selectable and usually very quiet compared to forced air furnaces.

Small fans pass air through those vents that is warmed by the hot liquid, giving the interior of the RV a pleasant and even temperature throughout each room. Usually, there are many zones that are controllable so its easy to control the heat.

exposed air heat exchanger for aquahot
This is what the backside of a heat exchanger looks like with the fan mounted in it. This exposed unit is for heating the basement and water lines and tank.

However, that’s just one part of the Aqua-Hot system. In addition to heating air it also heats the water in the coach. Inside the tank there are tubes that cold water runs through, this heats up the water. The hydronic fluid does not mix with the water as the tubes are separate; this is called liquid-to-liquid heat exchange. This in turn can provide unlimited on-demand hot water as long as the burner is running keeping the system hot.

Some hydronic system can also pump heated fluid into your diesel engine to preheat it before hitting the road. In addition to all this, the system also can use the preheat circuit to get the heat off the engine while driving. The system works in reverse taking engine heat and heating the boiler fluid. This way the coach can be heated through the air exchangers while driving.

The versatility of the system is impressive.  

The Many hydronic heating functions
Hydronic RV heat is very versatile and performs many heating functions

Pro Tip: We found 7 of the Best RV Water Heaters that we think your RV water system would benefit from!

What Are Problems Or Drawbacks To Hydronic Systems?

The biggest problem with hydronic systems is their complexity. Because of all the ways they can heat and move heat, there are lots of places where things can leak, pumps can fail, or electronics can malfunction. Luckily with multiple heat sources, there is at least redundancy and sometimes the system will partially work if one side fails. Maintenance is critical on theses systems and problems need to be addressed quickly to keep them operating properly. If they are not fixed quickly they can actually cause a lot of damage to your RV.

I put an entire video together showing some of our challenges but here are the high level issues.

Leaks – Because the system is fluid-based, lines can leak; they can leak in the boiler or in the RV. If they are connected to the engine, those can leak too. Since water is connected, it can leak as well, and if it’s diesel, that can leak too! Our system has had ALL of these fluids leak at one point or another. Its just the nature of the beast. These leaks however can cause major damage to your RV and need to be addressed quickly.

Electronics – There are three or more control circuits for the systems and problems with them are not uncommon. Relays failing, capacitors going or worse are possible. I have had to diagnose multiple electronic failures.

Pumps- Pumps are required to move the fluid (and heat). These pumps will burn out and need replacing. I have now replaced all the pumps on our 15-year-old unit.

How Long Does It Take for Aqua-Hot to Heat Water?

If the system is already hot, you will get hot water to your taps in a matter of seconds. Because its like a heat battery, it will heat the water instantly if its hot. If the primary burner is on it should last as long as the tap is on.

A full heat up with your Aqua-Hot heating system from cold however, including air vents could take around an hour, depending on the circumstances and size of the system. The system will heat up faster when switching on the electric and diesel power sources.

How Do You Winterize an Aqua-Hot System? 

Winterization of the hydronic heating lines is not necessary because they utilize an antifreeze solution that will not freeze. This is why its critical to use the correct fluid in the system.

The water heating size of the system will need to be winterized, however. This can be accomplished by flushing them with antifreeze. If you expect freezing temperatures be sure to do this or you will have serious damage to the system. DO NOT BLOW THE LINES OUT ONLY. Because of the design of the heat exchanger inside the tank, blowing out the lines will not remove all the water and can still cause a failure, always fill the hot water circuit with antifreeze!

Pro Tip: Prep your RV for the cold with these tips on How to Heat Your RV Tanks and Prevent Freezing.

boiler antifreeze
The working fluid within the system is an antifreeze that does not need to be winterized, winterize your water system however just like any other RV.

How Much Is an Aqua-Hot?

Hydronic heating systems are not usually possible to retrofit install so the cost is usually wrapped up in the RV. Usually, it’s around a 10k add; however, a replacement can run 8-10k. If our system completely fails someday I will consider replacing it with a residential on-demand boiler because they cost less than half of this.

Aqua Hot System | RV How To: La Mesa RV

Is Aqua-Hot in an RV Worth It?

Maybe. Is it the most comfortable heat in an RV, Yes. Is it quieter than forced air furnaces? Yes. Is it wonderful to heat with many different sources? For sure! Is the maintenance and reliability a problem, Yes to that too. If you’re handy, have lots of money, or are buying a new RV with a warranty, this system will offer you the best heating experience possible in an RV. But, if you want simple and reliable, hydronic is not the way to go.

What size system does your RV need to suit your travel party?  Drop a comment and let us know!

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About Tom Morton

Tom, a Pacific Northwest native, is our technical genius. Born in Washington and raised in Alaska before settling in Michigan. He's the man who keeps our operation running, both figuratively and literally.

With a background in Electrical Engineering, Tom specializes in RV solar systems and lithium batteries. He made history as the first documented individual to use a Tesla battery module as an RV battery. Tom has personally assisted countless RVers with system installations and has educated thousands more through his videos and articles.

Cinematography is another of Tom's passions, showcased in his work on the Go North series. You can see his camera skills on display in The RVers TV show on Discovery Channel and PBS where he also stars as a co-host.

Tom's mechanical expertise extends beyond RVs to boats, planes, and all things mechanical. He's renowned for taking on maintenance and repair projects single-handedly and is often spotted underneath RVs, making him the technical backbone of our endeavors.

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Richard

Wednesday 17th of May 2023

I have the Aqua Hot in my 2006 Beaver coach and the invention of the system is amazing, I can see why parts are still available with OEM

Mortons on the Move

Saturday 24th of June 2023

We love ours for sure!

John

Saturday 26th of February 2022

Having an on demand system is a wonderful luxury. Having really hot engine-heated water when you are stopping for lunch when travelling is especially convenient.

I look forward to a follow-up post "aqua hot vs oasis: which is the better unit?" .