Pros and Cons of Tankless water heaters in RV

CavemanCharlie wrote:

wra wrote:

wanderingaimlessly wrote:
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.

I have used changing water pressure less than 20 lbs to 60 lbs (a well pump system) with no problem regulating water temperature.

The main point is to have only the hot water faucet turned on. Having he hot and cold water turned on provides a path for cold water to the shower head, and causes the tankless heater to have less water go through it. That situation causes the tankless heating unit to turn off prematurely, and cold water continue to flow.(burr!) The tankless heater should be set to the desired shower head water temperature. Let it do its job.

So it sounds like in a home that it's a learning curve. Most people don't want to change their habits and don't want to learn new things.

That being said, it also sounds like it might not work as well in a RV where the parameters of flow usage and other things can change.

Unless tankless water heaters have changed considerably over the last few years, they have absolutely no temperature adjustments.

You have two designs, one with full on/full off burner that requires a min of .6 gpm flow or a modulated burner that varies the burner according to the flow.

Both however still have a minimal water flow required to turn on the burner.

Both use a very high BTU burner.

Both can only raise the water temperature to a certain point over the incoming water temp and the amount of temp rise is a factor of how fast the water is flowing. Slow moving water will have a much higher rise in temp, but now you risk the burner not staying on and you get a cold burst of bone chilling water or even worse end up with unanticipated scalding hot water..

In sticks and bricks instant water heaters are often installed with a tempering valve to help smooth out the cold/hot/cold variation with water flow.. Tempering valves are not typically built into water heaters.

Something else never mentioned is the need to periodically having to clean the tubes in a instant water heater. Water contains a certain natural amount of minerals (calcium, lime, iron) suspended in the water. Instant water heaters are prone to clogging from this mineral build up in the tubes. Water sources like unfiltered/unprocessed water wells can clog an instant water heater in a relative short amount of use.

In a RV, there is no advantage for using a instant water heater..

Standard 6 gallon RV water heater can easily supply you with 10-15 minute scalding hot shower. They are typically set to 130F-135F and you only need to mix a small amount of hot water into a lot of cold water to get a really nice steamy shower.

If done correctly, it works a bit like 5:1 ratio, 5 parts cold to one part hot. If you use .5 gpm of hot water, 6 gallon water heater can get you about 12 minutes of scalding hot water and as new cold water mixes it will cool down some towards the 15 minute mark and you simply reduce the cold water some..

I have found that if I turn on just enough hot to get water flowing and then add a bunch of cold just enough to make the shower head spray lightly three of us can get back to back (very little recovery time between) showers without anyone getting a cold shower.

Are you going to have a RV shower pin you against the shower walls like sticks and bricks?

Nope.

But, it will be plenty of water to get the cleaning job done..

Camping is not the same as home, there are compromises and if you want to be pinned to the shower walls then use the campgrounds showers or stay at home.

wra wrote:

wanderingaimlessly wrote:
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.

I have used changing water pressure less than 20 lbs to 60 lbs (a well pump system) with no problem regulating water temperature.

The main point is to have only the hot water faucet turned on. Having he hot and cold water turned on provides a path for cold water to the shower head, and causes the tankless heater to have less water go through it. That situation causes the tankless heating unit to turn off prematurely, and cold water continue to flow.(burr!) The tankless heater should be set to the desired shower head water temperature. Let it do its job.

So it sounds like in a home that it's a learning curve. Most people don't want to change their habits and don't want to learn new things.

That being said, it also sounds like it might not work as well in a RV where the parameters of flow usage and other things can change.

wanderingaimlessly wrote:
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.

I have used changing water pressure less than 20 lbs to 60 lbs (a well pump system) with no problem regulating water temperature.

The main point is to have only the hot water faucet turned on. Having he hot and cold water turned on provides a path for cold water to the shower head, and causes the tankless heater to have less water go through it. That situation causes the tankless heating unit to turn off prematurely, and cold water continue to flow.(burr!) The tankless heater should be set to the desired shower head water temperature. Let it do its job.

IMHO:

Given the history, reliability and efficiency of the existing LP/AC water heaters found throughout the RV industry for decades, going to a "Tankless" system is searching for a solution for which there is no known problem. :S

{The government does this a lot... but I digress.}
As always... Opinions and YMMV.

:C

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.

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.

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.

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

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

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