Shower valves and tankless

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morpho

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Okay, first I'll say I am aware of the shortcomings of Tankless units. But I have lived with one for 7 years and not had a problem with it at all.
I love the stupid thing!

BUT! I have been using it in a cabin/makeshift setting where I simply had Cold water pumping into it and out to a shower head. (no valve and no cold to mix into it)

Well I am about to do the plumbing to the bathroom in my new house and it's going to be a right proper shower with hot AND cold runnin' water!
My concern is what effect a pressure regulating or thermostatic valve will have on the Tankless.

(my preference would be to have old school manual valves hot and cold and the two simply meet and mix but these are no longer allowed by code....the tankless already serves as the scald protector as it is set to a specific temp and never fluctuates)

Anybody have some advice?
Some experience?

Thanks a bunch.
 

Cacher_Chick

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Not sure what you suspect, but a tankless works with a current model shower valve the same way that a tank heater does. We set either style water heater to 140F and leave it there.
 

morpho

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Thanks for the response,

I have read various concerns/problems with different valve types creating situations where the tankless unit is affected by the valve mechanism. I have read reports that they can make the unit shut off etc.
chances are there will be no problem, but it would suck to get it all set up and closed in the wall, only to find out that when mars is lined up with the moon and the valve is a pressure regulator type....I get (or more importantly my wife) a cold shower.
 

Jadnashua

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Some tankless heaters have built-in flow restriction. That can mean that the hot and cold are not balanced, and that can affect some valves. How often, I don't know. It's probably less of a problem with a thermostatically controlled valve, and may not happen with your setup.
 

morpho

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I guess the only thing to do is pick one, instal, hope for the best and be prepped to replace it with a different kind of valve.....after my wife has finished chasing me around the house after yet another cold shower!
 

Dana

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Not sure what you suspect, but a tankless works with a current model shower valve the same way that a tank heater does. We set either style water heater to 140F and leave it there.

There's no point to running a tankless at 140F, and that only exaggerates other issues, including more rapid scale-up and liming. Interactions with some types of anti-scald valves are also more likely due to the pressure difference issues as Jim noted.

While I agree a thermostatic valve is less likely to be an issue than pressure balancing anti-scald valves, set it up with the tankless set to 110-115F (as low as is tolerable for a tub-fill), with the thermostatic valve wide tweaked to the same or slightly higher temp as the tankless so that all the flow is through the heater. With the somewhat higher flow the tankless will then regulate temp better and have fewer flame out or delayed-ignition issues. If it's shower-only (no tub), you can probably set it as low as 105-106F and get satisfactory results. The flow through the tankless is somewhat higher, but the firing rate will be the same as if it were set up with higher-temp/lower-flow output.
 

morpho

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Hey Dana,
In a perfect world.... would old school pre-scald proof shower valves work best?
I know this is considered bad form when it comes to the code, but is this the ideal for tankless?

Thanks
 

Jadnashua

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The output of a tankless when it's reaching its max capacity can change radically based on the volume of water it is requested to flow...this would be radically transmitted to a conventional valve without one of the antiscald technologies in it...so, IMHO, a straight valve with a tankless would be worse than a required antiscald one. Even if your shower was the only hot water user, anything that affected the cold volume/pressure could affect the flow through the tankless and thus change the temperature outlet. The internal controls just can't respond that quickly in a tankless, a pressure balance antiscald valve can. Most thermostatically controlled valves need less than a second to compensate for variations, so you may or may not notice, but you won't get scalded.
 

morpho

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Hi jadnashua,

Thanks.
I get your point.

But I still contend that the tankless unit acts as the antiscald device simply due to the fact it is set to a max temp well below scald concerns.
My concern is the valve may shut off the gas flow or some other mysto effect and create an even worse problem...the COLD SHOWER!

If I had a straight valve in the shower I probably wouldn't even turn on the cold tap because I can set the temp at the tankless unit to a comfortable shower temp.
 

Dana

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If you set the thing to your preferred showering temp it's protective enough at high flow, less so at ultra-minimum flow (but still not a very real problem.) It may or may not meet code without an external secondary protection device though. A thermostatic mixing valve on the output of the water heater meets code in most places. Setting the mixing valve to 115F, and the tankless to 108F results in no mixing- 100% of the flow is through the tankless.

Shower mixing valves without internal anti-scald should work fine but the difference in cold side & hot side water pressure due to the impedance of the may make the fine-tuning of temp a bit difficult at high flow (= higher pressure drop through the tankless). That could be countered by plumbing in a ball-valve to insert an adjustable impedance on the cold side to roughly even-up the pressure differences. That approach could also allow you to tune out any interactions of an anti-scald shower valve with the tankless as well.
 

morpho

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The bucket of warm water I am currently using as a "shower" is looking better and better.

Okay, so this seems to be a complex unknown. So seeing as I don't know and things could go way sideways the more complex it gets, I figure the best thing to do is just install the thing and see what happens.
Maybe I will get one of those external valve jobs so I don't have to rip the wall apart when I need to change the thing out.

(what's with the obsession of burying the complex, leak and break down mechanism behind tiles and concrete board anyway???!!!)

I have built this house completely by myself and I am constantly amazed at how every little thing is riddled with unknowns and questions.
We should be extruding out perfect little house cubes by this stage in human evolution! But instead I can get an ipad that will talk to my coffee maker, but the house it sits in is still caught in the 19th century!

Thanks everyone.
 

Dana

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It's not that complex, and totally known- you're over-thinking it.

If you want the "endless shower" experience and the extra half square meter of cabin space, go with the tankless- the downsides are way over exaggerated. Real-world interations regarding mixing valves & anti-scald valves still relatively rare, and totally fixable if/when they occur without ripping out the tile work.
 

morpho

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Hey Dana,
I hear you what you are saying. And you are right, I am having to over think it.

My concern stems from having several neighbors who had to pull out their Tankless units and replace with hot water tanks simply because they couldn't get through a shower without having it turn cold.
They couldn't solve the problem, the plumbers had no idea why, the tankless manufactures had no solutions for them, so there must be an unknown in the equation somewhere.
So if the valves are part of the problem, how do I lessen the risk? What are the other factors that make for a cold shower?
So unfortunately I do have to over think it, because the plumbers and the manufactures don't seem to know. Or are unwilling to provide the solution.

All I know is that the unit I have been using in the cabin was flawless and the hot out line ran directly to a shower head, full blast hot water, no cold mixed in and it worked great. For a regular shower with all the valves and regular-ness it gets more complicated and the reaction of the unit is more complicated.

Anyway, cool. I will instal and see what happens.
 

Murphysf

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Hello

I just returned from staying at a friends vacation home.

I experienced a tankless water heater shower issued where the shower would be hot for about 1-2 minutes they get very lukewarm.

I was curious so I investigated the setup. The tankless water heater only sources hot water to the shower and tub. It is a single delta valve as the shower is over the tub.

There is a separate traditional water heater that supplies hot water to the rest of the home, all sinks, etc.

I noticed that when I run the tub the water stays hot, so I thought that the flow was limited by the shower head, which was the cause of the problem. I removed the shower head but still after a minute or so the water would go from hot to barley warm. I noticed that the shower arm gooseneck didn't look like a traditional piece of pipe, I believe it was part of the Delta kit and that it had a weird shape and most likely has a restrictor in it.

So I believe my friend has an incompatible installation.

The tankless water heater is a BOSCH unit and the temp knob was turned all the wat to the right.

So is the problem with the shower valve and or restrictor in the head or gooseneck or could there be an issue with the BOSCH tankless heater. It seems like since the tub temp is fine its not the BOSCH tankless water heater?

Not sure why they installed a separate tankless water heater for just the shower/tub and not have plumbed it to conventional tank water heater that supplies hot water to the two bathroom sinks and the kitchen sink. Note: The second bathroom only has a toilet and sink.

Ideas???
 
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Dana

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It's pretty common in Europe to have a medium sized tankless for the bathing & laundry area, and a fairly small one in the kitchen.

Thermo-mechanical feedback units like many of the low-end Bosch units have pretty lousy temperature control at low flow which may be part of why it behaves better with a tub-fill than a shower. But the anti-scald valves in shower mixers can interact with the inherent difference in water pressure induced by the restrictive heat exchangers in tankless water heaters, particularly smaller tankless units.
 

Ladiesman217

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It's pretty common in Europe to have a medium sized tankless for the bathing & laundry area, and a fairly small one in the kitchen.

Thermo-mechanical feedback units like many of the low-end Bosch units have pretty lousy temperature control at low flow which may be part of why it behaves better with a tub-fill than a shower. But the anti-scald valves in shower mixers can interact with the inherent difference in water pressure induced by the restrictive heat exchangers in tankless water heaters, particularly smaller tankless units.


I doubt that is a water heater problem.

I have an older ELM Aquastar tankless. Thermo mechanical feedback works fine as long as the thermostat probe assembly is good.

Similar water temperature thread below, but the output problem is just the opposite of this threads problem. Shower fine, but tub output is cold. Sounds like a valve related problem to me.

https://terrylove.com/forums/index.php?threads/moen-single-handle-no-hot-water.74064/

Here is another thread. The so called plumber even swapped out the old tankless heater with a new unit. Same problem after tankless swap.

https://terrylove.com/forums/index....s-still-not-providing-hot-water-to-tub.73490/
 

Jadnashua

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Depending on your home and how you do things, 105-110 degrees may not suffice for all hot water needs. Yes, it will work for a shower and maybe a tub fill. But, on some dishwashers that do not have internal heaters for the water, that low of a water temp will result in even some DW detergents from not dissolving, let alone the dishes getting clean. Same thing with some things in the washing machine. YEs, some of the tankless systems have remote control so you can change the setting, but it can be messy if you either forget, or then want to do something else simultaneously where now, the water is significantly hotter. Many washing machines and some dishwashers tend to pulse the water inlet, and if you're using hot, that puts a lot of stress on the tankless unit and often, won't be actually supplying hot water based on the cycle time and how long its been since there was hot (the pipes may have cooled). Living further north and especially in the winter when the incoming water temperature is lower just makes the whole thing harder...you'll use less cold to temper the water to warm, and increase the demand on the tankless system.
 
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