Atwood Tankless Hot Water Heater

[BILL49]

One of the issues with the tankless HW heaters is low flow temperature fluctuations that occur when you reduce or adjust water temperature at the point of use. The heater is dependent on flow to turn it on or off. Sometimes you won't have sufficient flow and you'll get a slug of cold water in the line between the heater and the point of use (particularly shocking if you're taking a shower !) The condition is compounded by the fact that the water has to travel from the heater to the manifold and then to the point of use (a long distance) requiring you to run the water until it gets hot (a waste of water and tank capacity). I'm considering installing a continuous hot water loop between the cold water supply line of the hot water heater and the hot water manifold in order to maintain a low flow thru the hot water heater. This could be accomplished with a small pumped connection at the manifold location. The pump could be switched on (say when you're taking a shower) and off when not in use. I think this might be a low cost solution to the tankless heater issues and much less expensive than installing a Truma. My only concern is that feeding heated water to the heater may eventually cause it to overheat (ECO cutout) if the circulating pump is allowed to run too long (ie; without using hot water), but I think the heater modulates based on incoming water temp. Any thoughts ? Has anyone done something similar ? Sorry for the long post !

[Welshes]

I like the idea. In our home, we have a tankless which is cold water supplied. I have a 3gallon heated header tank with a circulation pump which keeps hot water in the loop. I'd like to see how you accomplish this idea...thanks

[BILL49]

The idea is in the "thinking" stage right now, the rig is in the shop for warranty work and I've got a few other design issues to consider, so it may be a little while before I get to implementing it.. , but I will get back on the forum once I do.. Thanks for your input.

[erniet]

I hope one of you find a way to get constant hot water, this was another let down on this motorhome over previous ones.

[doughboy]

Do not think the Atwood takes inlet temp as a factor. I was hooked up to ground water which is approximately was approximately 45 degrees and then switched to the water tank on the coach which had warmed up to approximately 55 and the hot water heater then was hitting high limit. I tried multiple different things finally I just switched at the truma water heater, issues gone.

[zuckerburg]

Bill49 I have my Atwood dialed in pretty good. I had lots of problems when I first had it upgraded from a Gerard.
I went through the water supply and got rid of anything that could cause a reduction in flow. Not pressure but flow. This included the water regulator all quick disconnects and must important the water saver shower head. I bought the most ridiculous shower head I could find. This fixed my issues for the most part. I found that in Florida I still had issues so I ended up turning the gas down. This decreases the BTU the burner is capable of producing. In cold weather I turn it up a little. This doesn’t require a lot of messing with. I adjust it once or twice a year. Easy to do.
I would say this has been about 90% effective for us. Every once in awhile I go cold on me but seldom.
Hopefully this helps.

[BILL49]

That's interesting.. reducing the BTU output of the heater would at first, seem counter-productive since you're trying to maintain a certain hot water temperature at the point of use. A hotter supply temperature would require less hot water flow (a bad thing in terms of heater operation) mixed with more cold water to maintain a desired temp at the point of use. However, reducing the water temperature output of the heater would require more hot water flow thru the heater (a good thing) to maintain the desired temp at point of use. I could see where that change, along with removal of flow restrictions, could help improve the HW issue. The circulating HW loop however, would also improve the latency problems that plague most tankless HW systems. TNX for the input.

[TomnGerri]

You can install recirc line. Tee off hot water line at point of use and tee back into cold water supply line at the hot water heater. Make sure to put a check valve about 6 in from the cold water inlet on the recirc line. By adding the recirc line the water heater will work less to make the degree of Rise that is needed to achieve the temperature at the point of use. This is done in many commercial applications such as hotels restaurants and laundromats.

[BILL49]

Tom.. My thought was to install the loop right in the bay between the hot water supply line to the hot water manifold pumping to the cold water supply line to the hot water heater (with appropriate check valves). While this wouldn't totally eliminate the portion of the "cold water slug" from the hot water manifold to the point of use, it would affect all hot water points of use, be simpler to install and require a minimum of piping modifications. The circulating pump would be turned on prior to hot water use. I think by installing this loop you could lower the temp of the heater and not have to worry that the TCO would shut the heater off. Perhaps a simple mechanical timer switch in the pump circuit would prevent the pump from running for long periods of time when no hot water was being used. I'm thinking the whole job could be accomplished for less than $100-$150. Thanks for your input.

[TomnGerri]

Bill,
Doing it your way would probably not require a pump due to the short run of piping, the water pressure itself should be sufficient. If not a flow switch could be installed and wired to small pump the pump would only turn on once flow was made across the switch. Once the demand was finished the pump would shut down due to no flow and start again once a call for heat was established from the heat exchanger. just my humble opinion

[card16]

If one of you are successful at installing a loop that actually resolves the tankless H2O heater cold slug issues, would you then draw out your solution showing the additional piping and/or pumps and include installation instructions. That would be helpful. Theories are good and sound right on paper, but practical application will prove out those theories. Thanks in advance, I will continue to follow this thread in anticipation of your results.

[gordonsick]

People interested in this question should note that two different solutions have been discussed on this forum.

One solution is by Oscarvan who describes the solution in his Dragonship blog https://dragonship.blog/modifications/hot-water-system/ It is quite similar to the idea being discussed here.

The other solution has been discussed by me at http://www.forestriverforums.com/for...er-119716.html It involves installing a thermostatic shower valve, which takes advantage of the fact that the slug of water is just cooler and not cold, so a temperature valve that keeps the shower temperature constant is all that is needed. At least one other forum user has also done this installation (I used a Delta and I think he used a Grohe, but both were thermostatic shower valves.) Both of us are happy with our installations, which are much simpler (and cheaper, and more efficient) than installing an extra heater into the circuit.

–Gordon

[card16]

Gordon, thanks for the additional information and the links, I appreciate it.

[TomnGerri]

Another way maybe to install a thermostatic mixing valve instead of having to change out the entire shower valve

[TomnGerri]

Originally Posted by TomnGerri

Another way maybe to install a thermostatic mixing valve instead of having to change out the entire shower valve

[BamaBob]

I have a even better idea

Replace the Atwood piece of junk with a Truma and your problems will be over! We have had a Truma now for 2 years and absolutely love it! Truma is now the standard Tankless Hot Water Heater in all Berkshire models

[gordonsick]

Originally Posted by TomnGerri

Another way maybe to install a thermostatic mixing valve instead of having to change out the entire shower valve

What are the inputs for the thermostatic mixing valve? Hot and cold?

Where do you put this valve? If it is in the shower, you have to do as much work as if you replace the existing shower valve. If the valve is in the wall and then feeds the shower valve, how do you adjust the temperature?

Just a little confused on how to make this work?

–Gordon

[TomnGerri]

Gordon you don't have to put it in the shower you just take it and mount it where the hot water heater is then you have a constant set temp throughout your camper

[gordonsick]

Originally Posted by TomnGerri

Gordon you don't have to put it in the shower you just take it and mount it where the hot water heater is then you have a constant set temp throughout your camper

OK. I see now.

But that means I'd be washing my dishes at the same temperature as I wash myself. Maybe that's not a big problem.

The plan must be to blend in cold water with the water that comes out of the tank.

–Gordon

[David N Dianna]

We found that if you turn the hot water on in the sink you can adjust the hot water temp by how much flow you allow through that faucet.
If you want hotter water in the shower turn the faucet down, if you want cooler then open it up more.
This has worked for us for the last 6 years.