Oasis Hydronic Heating Explained

[MikeGriffin]

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.

[SWag]

Nice summary Mike, thanks for sharing.

[PDR John]

Mixing valve

["007"]

Welcome to the forum and irv2, Mike.
Here is a 2015 Brochure and Owners Guide for you, sorry no 2016's yet.
I will add your over view of the Oasis system in QT's # 3 for future reference.
In my signature below you will find links to many more for your future Newmar.
Nice coach your looking at are you keeping the two bar stools?
Good luck in 2016 if you can wait that long, enjoy the forums.

[VP Chianese]

Thanks for the detailed description.

We bought our coach used just a few months ago so sometime there are things done by the last owner that need to be let's say "undone".

We had plenty of hot water when the heat was on but not when the heat was off. Also we had limited hot water in the shower as in less than two minutes from can't stand it hot to can't stand it cold. The dealer chased these two problems for several weeks. Not realizing that they were separate in cause. The reason for hot water with the heat on was that the tank was heating for heat thus hot water was abundant. But the dealer never tried with the heat off because it was 35* outside. So we got that squares away and they replaced the sensor for hot water which solved the problem. But not quite. The shower was still a problem but the threes sinks were not. They had all you could stand but the shower got cold after a few minutes. Now for the easy repair. Went to Lowe's and bought a shower head that was a 1.5 GPM max flow rate. Now we can have a sauna with steam for as long as we want. Seems the old shower head was just to high of a flow rate.

[Mr JP]

Very Nice and easy to understand !! Thanks for the great explanation.

JP

[spsm]

Thanks for the input Mike. Love this forum.

[Falcon190]

Thanks. Your description is spot on. I replaced my old Aquahot with a new Oasis last March at the ITR factory service center in Vancouver, WA. So far it seems to be a much better unit. And easier to service.

[Lee L]

Thanks for taking time to post this, good stuff. I too have learned more than I wanted to know about the Oasis system in the year and a half we have owned ours. Had more than a little trouble which appears to have finally been fixed by replacing the flame sensor, for the second time...seems that the first replacement was intermittent which caused much tail chasing in the troubleshooting department.

There is one thing I don't understand, and not even Oasis tech support can explain it. We usually keep the burner switch on, since we like lots of hot water/heat when we need it. The burner will come on pretty regularly for a minute or two, even when no heating/hot water is being called for. I can understand why the burner comes on when the furnace is calling for heat, or a hot water faucet is on and calling for hot water. Our coach stays in our barn and I can hear the burner fire off for a few minutes every couple of hours.....even when the thermostats are set to off, and there is no one using water. It does this all the time, if the burner switch is on, the burner is going to run every couple of hours or so whether needed or not. Makes no sense to me.

[VP Chianese]

Originally Posted by Lee L

Thanks for taking time to post this, good stuff. I too have learned more than I wanted to know about the Oasis system in the year and a half we have owned ours. Had more than a little trouble which appears to have finally been fixed by replacing the flame sensor, for the second time...seems that the first replacement was intermittent which caused much tail chasing in the troubleshooting department.

There is one thing I don't understand, and not even Oasis tech support can explain it. We usually keep the burner switch on, since we like lots of hot water/heat when we need it. The burner will come on pretty regularly for a minute or two, even when no heating/hot water is being called for. I can understand why the burner comes on when the furnace is calling for heat, or a hot water faucet is on and calling for hot water. Our coach stays in our barn and I can hear the burner fire off for a few minutes every couple of hours.....even when the thermostats are set to off, and there is no one using water. It does this all the time, if the burner switch is on, the burner is going to run every couple of hours or so whether needed or not. Makes no sense to me.

Ours does exactly the same thing. I think it is keeping the tank at temp. demand or no demand. But I could be wrong so that's a good question.

[OC Bill]

Originally Posted by VP Chianese

Ours does exactly the same thing. I think it is keeping the tank at temp. demand or no demand. But I could be wrong so that's a good question.

X2

Bill

[MikeGriffin]

When the burner switch is left in the "on" position, the burner will continue to operate until the coolant reaches the desired temperature at the top of a set range, at which time it will turn off. When the coolant cools down to the temperature at the bottom of the range, it will turn back on and will stay on until either the burner switch is turned off or the high-range temperature is reached. If the burner is turned off at the switch while it is running, it will enter a two-minute cool-down stage before it completely turns off.

[wagonmaster2]

Wow Mike, that's some explanation. Greatly helps me understand what I will be facing in 2-3 months. Makes my current gas furnace and gas/electric water heater seem very archaic. Think I'd better copy your explanation for my 4018 file and save it.

["007"]

Its always in the QT's # 3 thread look under AC's, Heat Pump Heating Section.