Saturday, September 12, 2015

Oasis Hydronic Heating

Okay, I'm cheating on this post.  It's just a cut n' paste of a post I made in January 2015 on the irv2 forums.  I was curious about how the Oasis Heating system worked and so I did a bit of research and wrote it all down before I forgot it.  It gets a little bit detailed, but you can always just roll your eyes and go read something more fun!  I tried my best to explain things at a level so that even I could understand it because I'm not a mechanic or a plumber.

Oasis Hydronic Heating Explained

It wasn’t too long ago that I had questions about the basic operation of the Oasis Hydronic water heating system. After getting some great responses on Facebook, reading articles on irv2 and doing some research on the Internet, I think I have a basic understanding now about how it all comes together. I've seen articles that provide a great amount of detail, but thought it might be helpful for some to offer something that's more of an overview.

The Oasis Hydronic Water Heating system installed on Newmar RVs is located in the basement of the motorhome, usually on the driver's side. It is housed in a green container and is made up of two "sides": a Heating Module and a Distribution Module. These are back-to-back, with the Heating module being the side you see when you open the compartment.

Within the Heating module is an 8.2 gallon tank that contains coolant. The coolant is basically a mixture of antifreeze and water. The Heating module also contains a 15kW stainless steel burner. It is powered using 12VDC, but uses diesel fuel to heat the coolant. The diesel fuel is taken from the main RV diesel tank - the same one that powers the motorhome's diesel engine. For this reason, the Oasis also has its own built-in fuel pump and an exhaust to expel the smoke and smell.

The Heating module also contains two 1500 watt "immersion" elements that provide secondary (to the burner) heat. These require a 120VAC power source. 

The Distribution module literally uses three pumps to distribute the coolant to different zones throughout the coach. It has a heat exchanger that is used to heat water as it passes through it. This is where water is heated for sinks and the shower. It also has a function that can provide heat to pre-heat the engine.

The Oasis can be used for three things: 1) heat the RV, 2) heat water for sinks and showers and 3) pre-heat the engine if the option is installed to do so.

To heat the RV, the secondary elements and/or the burner are used to heat the coolant and then send the heated coolant to a maximum of five different zones within the coach. When it gets near an output vent, a fan pushes air over its own heating coil (contains the hot coolant) and the warm air enters the cabin. The coolant then returns to the Oasis tank to be re-heated.

To heat water, the Oasis takes water from the RV's water tank and runs it through the heat exchanger in the Distribution module. The heated water is then sent out to the RV's hot water line.

When equipped, the Oasis can pre-heat the engine. When the engine pre-heat switch in the coach is turned on, the engine pre-heat pump and the coolant pump will be activated and heated coolant is sent to the engine to warm it up. (That's about as much as I can tell you about this!)

The Oasis also has a feature that allows engine heat to be used instead of using the elements or the burner. With the burner switch in the cabin turned to "On", the burner will heat up and will then cycle to off . At that point, heat from the engine is transferred so that it can heat up water and even the coach.

The control panel in the coach has a Burner switch, an "AC" switch and, if equipped, an Engine Pre-Heat switch.

The Burner switch turns the diesel burner on or off. Once the burner has been activated, the Burner LED light will come on.

The AC switch controls the two secondary heating elements. This switch has three positions: Both off, one on, or two on. The AC heat LED will turn on when the element(s) have been activated.

If the engine pre-heat option has been installed, this switch will turn on the engine pre-heat pump. Note that it won't work, though, until the coolant has reached a preset temperature.

For people who don't think their hot water is hot enough, there are several things to try: 1) turn on an additional AC (heating) element on the control panel, 2) turn on the burner - you may be heating the coach at the same time and you need it to get maximum heat, 3) remove the plate behind the shower water handle and see if there is a restrictor (usually red) that restricts how much hot water will flow and 4) adjust the mixing valve inside of the Distribution module. The only one of these that probably needs some explanation is the mixing valve adjustment. To get to it, you'll likely have to climb inside of the storage compartment behind the Oasis (from the curb side), remove a panel and then remove the Distribution module's cover. The mixing valve is located inside of the module (see some other posts for details on its exact location; I think it's on the lower right and it's gray in color). The mixing valve is factory set to 120 degrees, but it can be adjusted from 100 degrees up to a maximum of 145 degrees. Turn it clockwise to increase the temperature.

I hope this answers the basic questions that some folks want to know. If I've put out any incorrect information, please reply and let me know. Feel free to expand on any areas, too.


  1. The collant in the overflow tank is below the level got 'cold". You said the coolant is just a mix of antifreeze and water. Does Oasis sell a regular coolant or do you mix your ow. What proportion?

  2. I was told there is only one kind of coolant that should be used with Oasis. It comes either as a concentrate where you mix 2 to 1 (the explanation is on the jug) or you can buy it pre-mixed where you just pour it in. Some RV repair people don't know about the reservoir in the back.