Pros and Cons of Tankless water heaters in RV

[NamMedevac_70]

Thank you for your replies if any.

[valhalla360]

goducks10 wrote:
As far as I know tankless only run on propane.

They do make electric versions but it takes a lot of power to heat water. 30amp rigs won't have enough and 50amp rigs will only be able to power the lower flow models.

We had a propane unit on our boat and almost never used it because it was almost impossible to get hot but not scalding water.

A possible compromise might be the inclusion of a 1/2 gal mixing tank. That way the temp changes are at least gradual.

[wanderingaimles]

wra wrote:
I notice that some answers mention having no hot water and suddenly having too hot water, having to mix cold water, or needing high flow to turn unit on. All these problem are due to not having the the correct hot water unit or not having it set properly. The correct gpm flow should come on less than half a gallon per minute. The temperature should be set to the temperature desired with no mixing of cold water. That way, the water takes less time to get to the point of use, and does not waste electricity or propane heating water to temperature not needed. That is the purposes of tankless heaters; that you do NOT heat water higher than you need, as well as not keeping water hot when you are not using it. This applies to RV and stick home use.

Your in florida, for home or rv use you only need to heat the water 30-40 degrees to get the temp you want, from an rv tank you may not need even that much, but as temperature range changes increase, the difficulties regulating it do as well.

[wanderingaimles]

To explain the all hot or all cold.
Flow rate turns on the unit, you have to meet the minimum flow rate through the heater or it does not come on. In most cases that is around .6 gpm in small units, but in the first gas home model I got it was 1.4 gpm.
.6 gpm to a showerhead is less than half the flow rate of most showerheads. RV showerheads can be lower flow to conserve water, but Girard, the biggest brand of RV tankless heaters warns that rv users with low flow showerheads will need to remove any restrictors from the showerhead.
At .6 gpm the water comes out with no force, but because the flow is low, the water has more time in the small heating chamber to be warmed. The faster that water flows through the chamber, the less heat it can absorb.
So if the flow rate allows a 50 degree rise in temp that makes a comfortable shower or sink temp IF the water entering the unit is about 50 degrees, if the incoming water is 70 degrees it will exit at 120, if it enters at 40 degrees it will exit at 90.
The RV units try to regulate the temp by modulating the flame from the propane, in an attempt to control how much heat is applied to the water to allow more variation in the final warm water. How successful they are is a matter of opinion.

sample flow chart of tankless water heat flow vs temp rise this is for a single point of use home electric unit, but sized similar to the rv units,
elec unit.

Note usage is listed for region where it is to be used, rv cant specify that, it moves around.
Look at amount of heating, flow at that temp change, and then decide if you will be able to live with those parameters.

[Lantley]

wra wrote:
I notice that some answers mention having no hot water and suddenly having too hot water, having to mix cold water, or needing high flow to turn unit on. All these problem are due to not having the the correct hot water unit or not having it set properly. The correct gpm flow should come on less than half a gallon per minute. The temperature should be set to the temperature desired with no mixing of cold water. That way, the water takes less time to get to the point of use, and does not waste electricity or propane heating water to temperature not needed. That is the purposes of tankless heaters; that you do NOT heat water higher than you need, as well as not keeping water hot when you are not using it. This applies to RV and stick home use.

Tankless for RV's maybe a good idea on paper but in reality there are lots of obstacles. Firts issue is the incoming water pressure varies with the campground. The end user does nothave full control over the incoming water pressure

[Shearwater]

If your vehicle runs on diesel there is a diesel-powered water heater available. This works extremely well - instant hot water with no tanks.

[wa8yxm]

Pro: You never run out of HOT water unless you run out of Water
PRO: it only burns energy (usually propane) when you call for hot water

Cons: Burns a lot of propane when running (generally less over all however)
Con: May not activate at low flow rate

[time2roll]

NamMedevac 70 wrote:
Thank you for your replies if any.

what issue are you trying to resolve?
My family of 3 does fine with 6 gallon w/h. Even a couple more would seem manageable.

[wra]

I notice that some answers mention having no hot water and suddenly having too hot water, having to mix cold water, or needing high flow to turn unit on. All these problem are due to not having the the correct hot water unit or not having it set properly. The correct gpm flow should come on less than half a gallon per minute. The temperature should be set to the temperature desired with no mixing of cold water. That way, the water takes less time to get to the point of use, and does not waste electricity or propane heating water to temperature not needed. That is the purposes of tankless heaters; that you do NOT heat water higher than you need, as well as not keeping water hot when you are not using it. This applies to RV and stick home use.

[Lantley]

Crowe wrote:
We also have tankless in our house. Never again. It wastes tons of water to get hot-much more inefficient than heating a tank. The up side is we don't have this big tank in our basement, but that's about it.

Tankless is less efficient in terms of using additional water. I agree it takes a bit longer to get hot water at the faucet. THe amount of time it takes to actually have heated water Depends on how far away the faucet is from the tank. A recirculate line can solve the wait and waste issue.
However tankless is way more efficient vs. keeping 40 gallons of water hot 24/7/365.

[Crowe]

We also have tankless in our house. Never again. It wastes tons of water to get hot-much more inefficient than heating a tank. The up side is we don't have this big tank in our basement, but that's about it.

[wanderingaimles]

I went that route in S&B,,,,, never again.
You can not just run warm water at a lavatory, either way too hot, or running water wide open on both taps because the heater requires a specific flow in gpm to turn on, once its on, its full hot, there is no mid point, so you have run large amounts of cold to balance it.
For us at home, in the winter we run the hot only, to get a lukewarm shower. 45 degree water in, needs a 50-55 degree rise to be warm so the 13200 watt unit can only meet that at a .6 gpm flow.
In the summer, 65-70 degree water in, we must run the full 1.8 gpm at the heater and then add cold to keep from having the systems safeties cycle the unit off and on to avoid scalding. Which if that happens, you get a cycle of full hot, then all cold, then all hot.

I cant see it ever being a good idea in any system trying to conserve water. We have learned to use it at home, and we dont really have a good place for a conventional unit, otherwise I would have tossed it.

[goducks10]

As far as I know tankless only run on propane. Not sure how much they use but being on FH you still need propane.
FWIW my wife and I have never run out of hot water with our 10gal WH. I can't imagine needing to stand in a small RV shower that long anyways. Get in and get out.

[Desert_Captain]

Unless you spend all of your time in a full hook up site there really aren't many "pro's". The manufacturers like to brag that they provide unlimited {yeah, right} hot water but...
"unlimited" is a seriously challenged word truth wise, just sayin.

An unlimited hot water supply necessitates unlimited fresh water supply so for this to work you must be hooked up. The second consideration is where does all of that "unlimited" hot water go once you have used it? In a full hook up site no problem but anything else and you are simply chasing your tail as you continuously fill your gray and black tanks.

The hot water starts pretty quick but "instant"... not so much. It will always take a bit to get the flow at a temp you can live with {as in stand in without screaming}. 🙂 Now if they would sell you a tankless system for the price of an LP/DC system the tankless would almost become a viable option for the RV Park crowd but price both systems folks... ain't gonna happen. :R

I would have no problem with an on demand/tankless hot water system for my house {even though they cost a lot more - frankly with a solar system making a great deal more sense but I digress}} but for my motorhome and the way we use it, it just does not make any sense.

As always... opinion s and YMMV.

:C

[Diamond_c]

I too am very interested in what people have to say about this. I’ve been wondering about this myself.