On demand water heater swap.

Hi folk, we have a shower nuance model 3700 RLB fifth wheel, and I would really like to switch out the hot water heater from the factory one to a 120v on demand water heater. I guess my question is, has anyone ever done this before, and if you have, what model of heater did you replace it with. The reason why I want to switch it is because the factory heater doesn’t supply us with enough hot water. You might get appropriately 3 minutes in the shower, our previous fifth wheel had a lot better hot water heater and I would like this one to have the same capacity and hot water time frame. Thank you in advance.

we have a shower nuance model 3700 RLB fifth wheel,

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I'm guessing auto correct changed Sundance into shower nuance.

GarryN2016 said:

Hi folk, we have a shower nuance model 3700 RLB fifth wheel, and I would really like to switch out the hot water heater from the factory one to a 120v on demand water heater. I guess my question is, has anyone ever done this before, and if you have, what model of heater did you replace it with. The reason why I want to switch it is because the factory heater doesn’t supply us with enough hot water. You might get appropriately 3 minutes in the shower, our previous fifth wheel had a lot better hot water heater and I would like this one to have the same capacity and hot water time frame. Thank you in advance.

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Something is not correct about your current setup. Some possibility if heating correctly, is the HW bypass in wrong position, or the check valve on the HW heater is bad.

GarryN2016 said:

Hi folk, we have a shower nuance model 3700 RLB fifth wheel, and I would really like to switch out the hot water heater from the factory one to a 120v on demand water heater. I guess my question is, has anyone ever done this before, and if you have, what model of heater did you replace it with. The reason why I want to switch it is because the factory heater doesn’t supply us with enough hot water. You might get appropriately 3 minutes in the shower, our previous fifth wheel had a lot better hot water heater and I would like this one to have the same capacity and hot water time frame. Thank you in advance.

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I think you’ll be making an unwise choice switching to an on demand tankless water heater. For regular residential use, the tankless is the only way to go. We have used them for over 20 years and swear by them.
For rv setups, their reviews are not good. As was suggested, trouble shoot your current system and find out what’s wrong. We all use the tank water heaters and most think they are sufficient.

plenty of super hot water in our RV, I'd do so more toubleshooting

Cold weather can be a problem. If the incoming water is very cold, you'll use more hot water in the mix to get a comfortable temperature. If you keep your fresh tank full and run from the pump, the cold water won't be as cold and your hot water will last longer.

Water heaters come in various sizes, with 6 gallon, 10 gallon, and 12 gallon being commonly used. Obviously a 12 gallon water heater will last twice as long as a 6 gallon. You can determine the size by removing the outside cover and looking at the model #. That'll also be helpful as the size may be important when selecting a replacement.

Dahillbilly said:

plenty of super hot water in our RV, I'd do so more toubleshooting

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I spent all last summer messing around with the water heater, I double checked the by passes, and turned on both the electrical and propane switches so it would get both heating systems working to reheat quicker, but we only get approximately three minutes of hot water. I felt the bypass piping to make sure that it wasn’t seeping by, and even if it was a 6 gallon heater, it should definitely give you more than three minutes of hot water. It’s very frustrating, we just got this fifth wheel last year, our other fifth wheel was totaled off by a gang of squirrels over the winter, but it had plenty of hot water capacity. I just don’t know where to go next with this, short of pulling it out and getting a different type of water heater.

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Dahillbilly said:

plenty of super hot water in our RV, I'd do so more toubleshooting

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I spent all last summer messing around with it, and couldn’t get more than about three minutes of shower time out of the hot water. I checked the bypasses for leakage, by feeling the lines for hotness, and even tried activating both the electric and propane heaters to see if both together would make it regenerate the hot water quicker. But to no avail. I just don’t know what to do next, I’ve asked all of our fellow campers in our RV park but everyone thinks it’s just small capacity. That’s why I’m to the point of just switching it out.

Let's assume you have a 10 gallon water heater. Also assume the mix is 50% and 50% cold. That would mean you can expect to run out of hot water after 20 gallons, or maybe a bit less.

Now assume you've got good water flow and are using 4 gallons/minute in your shower.

That would give you 5 minutes of shower time.

And if it's cold, your mix is probably more like 60% hot / 40% cold and the shower would get cold that much faster.

If you have an Atwood water heater, I think the thermostat can be changed to deliver 140 (F) instead of 130 (F), which would help.

Have you checked to see if both valves on your external shower are completely closed? If the cold is partly open, it can mix into the hot water lines and cool down the water.


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If you’re using 4 gallon/minute, you need to get a new shower head with a lower flow rate. And if you have a DSI water heater, turn on both the electric and propane heaters before showering.

In the 11 years we had our 3670 with a 12 gallon water heater, we never had a cold shower, even when we took ours right after the other person.


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boatto5er said:

Have you checked to see if both valves on your external shower are completely closed? If the cold is partly open, it can mix into the hot water lines and cool down the water.


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Yes, I had checked extensively on everything I could possibly think of. I did check the outside shower for any leakage and there wasn’t. I guess the frustrating part is that before we had this ever, we had a smaller keystone copper canyon and it had plenty of hot water. This sundance has three shower stations in it, and also has a bigger sleeping capacity than our other ever, one would think that it would have a hot water heater capacity to accommodate the camper.

If you're looking for help, get the manufacturer/model # of the water heater. Remove the outside cover to find the label.

with the water in the tank, fully heated to a reasonable temperature, you should be able to open any faucet in your rv (just the hot water and NOT the cold), and have about 4-6 minutes of run time before you notice it getting cold.... mixed with cold to make it comfortable for a shower should give you at least 10 minutes before it starts to get too cold to shower in ....

with that said, ALL the plumbing in the trailer could be correct, but if either the cold water in-feed, or the hot water out-feed lines INSIDE the water heater is faulty, it will have the same symptoms you describe...
as well as if someone plumbed the water heater into the trailer plumbing, backwards, it will have the same symptoms....

a higher temp for the hot water will require more cold water to cool it down enough to shower in, which this can increase the amount of shower time you would have, and just the opposite is true if the water heater only heats the water to a comfortable level, without any need for mixing with cold water.... in which case, a 4 minute shower is about what you will have before it starts to get noticeably colder...

What is the gallon per minute output of the shower head? I replaced the cheap RV shower head (in both Bighorns with a 12 gal water heater) with a quality water saving unit from Lowe’s. As I recall it’s output is 1.75 gpm meaning on 50/50 hot/cold one should have a comfortable shower for at least 15 minutes IMO.
The two of us can take back to back showers without wanting for additional hot water. Just saying
IMO if you have confirmed the tank is plumbed correctly and there are no blockages of the hot water outlet I’d be swapping out the hi/lo limit switch first and as a last resort replacing with a new RV unit before installing a demand water heater in an RV unless maybe if I was on a seasonal site.
Camper friend of ours actually added an additional heated storage tank in his MH to supplement the on demand hot water heater because the on demand heater lacked on performance in his opinion


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