30A On Demand Water Heater not working great

So we just bought a used 1987 Shasta Revere 21' in GREAT shape.  All exterior and interior has been repainted, etc etc.  Anyway, the owners previous to the people we bought from installed an on-demand water heater that requires 30A service.  We finally took it camping last weekend and the water barely got lukewarm.  Either:
1) the water pressure coming in was too high (although I adjusted down to a pretty minimal level I thought)
2) the water coming in was too cold - although I can't believe that.
3) We didn't let it run long enough - first time camping, not knowing capacity of grey water tank, we didn't want to waste space.

It did get pretty warm for a few seconds while we ran the water but then it went back down to lukewarm.

Any suggestions?

Thanks much!

Yes....those units are very sensitive to flow rate thru the unit...also if the deposits are built up it acts like an insulator and slows the heat transfer a lot.
Try slowing the flow down on the hot side of the faucet..
If there are deposits in the unit they can be cleaned, however, I never have done that just heard that it can be done.
Good Luck.

George

Is it 30A 120v or 30A 240v?

This is interesting, I didn't know that there was such a thing as a "Tankless" water heater for a towable RV.  I have a gas unit at our house in Wyoming which we love but...it takes a whole lot of energy to heat that water up "instantly".  I was going to put an electric tankless into a piece of rental property a year or so ago until I discovered that the residential units require "3" 30amp circuits to operate, that's 90 amps of power!!!

I'm not sure how you would get an electric tankless to work on an RV, somebody explain the unit if you can.

Thanks

Simple answer - either raise the temperature of a trickle of water from cold to hot, or a larger flow from cold to not-so-cold.  There just aren't enough BTUs available in a 3600 watt heater to do anything else.

So Lou, is what you're saying is that "It Won't Work"?

We do as much boondocking as we can so we really wouldn't have much use for a tankless in the first place, we just don't use that much water when we're going self contained.  If you were full timing in an RV park I guess it might be nice but my 10 gallon Atwood recycles so fast anyway when running on gas and electric I'm not really sure we could run it out or at least not for long.

The short answer is "It won't work"

Here's the long answer ... 

30 amps @ 120 volts provides 3600 watts or 3.6 Kilowatts

1 Kw/hour will provide 3412 BTUs.  3.6 Kw/h will provide 12,283 BTUs.

It takes 1 BTU to heat 1 lb of water 1 degree F.  Since water weighs 8.3 lbs per gallon it takes 8.3 BTUs to raise the temperature of a gallon of water 1 degree.  Or 332 BTUs per gallon to raise it's temperature 40 degrees, say from 60 to 100 degrees.

It will take one hour for a 30 amp circuit to raise the temperature of 37 gallons of water by 40 degrees.  That's 0.62 gallons per minute.

A low flow showerhead uses 1.5 - 2 gallons per minute.  That's more than the 0.62 GPM the water heater can deliver.  So you'll wind up with a shower that's either very cool or with a very anemic water flow.

If the heater was 30 amps at 240 volts, that would double the amount of heat it can produce.  But you'll still only have 1.2 GPM available at full temperature.  Still not enough oomph to really do the job.

I've seen propane powered tankless water heaters, and they work because there's more BTUs available with propane.  You might be able to use one of these in a RV, but I don't think they're covered under the RVIA code.

Thanks Lou,
I didn't think about the BTU's & amps...your 100% correct. In that application It can't work properly. As you stated tank-less, W/H's require massive amount of BTU's for the duration of their use propane or electric..A residential unit will need probably 60 or 90 amp 240 volt circuits. If on propane they consume 60 to 120 Btu's which is somewhere around 60 to 120 CU' of gas per hour of use, if I remember propane is a little under 99K btu's per gallon & some where round 41/2 lbs per gallon..
The premiss is that they save due to the lack of a holding tank use as no use of water means no energy expenditure.
They are pretty big in Europe but are having a hard time catching on in the states.
Thanks for catching my incomplete answer and adding the correction I didn't do.. : :'(

George

Lou Schneider said:

...I've seen propane powered tankless water heaters, and they work because there's more BTUs available with propane.  You might be able to use one of these in a RV, but I don't think they're covered under the RVIA code.

Click to expand...

Sigh! RV tankless water heaters have to be the most understood things on RV forums.

There are now six tankless water heaters approved for RV use available. The Aqua Hot actually is a diesel fired (the others are propane fired) hydronic heating system that also heats domestic water. The Aqua Hots are notoriously expensive to buy and maintain but owners usually swear by them.

Girard makes one model. It is the one most RV manufacturers have been installing in RVs (other than the Aqua Hot). It can be fitted into the same hole both 6 and 10 gl. conventional water heaters use. Water temperature with the Girard is regulated by adjusting the rate of water flow (all others regulate water temperature by blending hot and cold water).

Precision Temp now has two models. The RV 500 has been around for a while and installs in the same hole that 10 gl. conventional water heaters fit into. High wind and winter kits are available to prevent wind from blowing out the flame and to protect the unit from freezing in weather down to -10F.

The RV 550NSP was recently introduced. Instead of having to be mounted in an external wall like most other water heaters, this unit can be installed on the floor anywhere inside of the RV. It is vented through the floor and the exhaust is routed under the RV to the outside wall much like a generator exhaust. Since it is entirely inside the heated area of the RV, there are no concerns for freezing, wind, rain, etc.

Atwood has teamed up with Precision Temp to develop two tankless water heaters to be sold under the Atwood label. One is rated for up to 45,000 BTU and the other is rated for up to 50,000 BTU. The 50,000 BTU model is also equipped with a winter kit (I don't know how low of a temperature it can go without freezing yet since I'm still getting details from Atwood). Both models will fit in a hole designed for both 6 and 10 gl. conventional water heaters. The prices are between the Girard and the RV 500.

You all are correct that electric tankless water heaters are not practical for RVs due to the lack of available power.

It's not only misunderstood by people who DON'T have them - also by those that do (until they get used to thinking backwards )
The turn the hot water UP to cool it down and turn it down to heat it up is a tough concept
when the water hitting certain areas is too cold or too hot
and you've been doing it the other way all your life !

IIRC, our's is 12v and uses propane to heat the water... http://www.mvprv.com/products/destiny/GIRARD-tankless.pdf

and I promise it works ! Too well sometimes !

Typically I will  not turn on the cold at all... and depending on the source water temps, I have a switch to set it to either low flame or high flame as a starting point...

so look your's up on the net and find out how to adjust - and in my case remember to turn the propane on !

Lou , 1 BTU will raise 1 gram or cc of water 1 degree c in 1 min.  Think metric

Nope, 1 BTU is the energy needed to raise 1 pound of water 1 degree F.  Or about 1055 joules.

A Calorie is the energy needed to raise 1 cc of water by 1 degree Celcius.  Something to think about while you're munching on that Big Mac. 

http://www.engineeringtoolbox.com/heat-units-d_664.html

You are right Lou.  My memory is getting bad. Getting mixed up. Thank you

JohnBoyToo said:

It's not only misunderstood by people who DON'T have them - also by those that do (until they get used to thinking backwards )
The turn the hot water UP to cool it down and turn it down to heat it up is a tough concept
when the water hitting certain areas is too cold or too hot
and you've been doing it the other way all your life...

Click to expand...

This is a perfect example of the misinformation that abounds. What you said about water temperature adjustment applies ONLY to the Girards (I even said that in my previous post)! The other five tankless water heaters approved for RV use are adjusted by blending hot and cold water, the same as conventional tank type water heaters.