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Thread: shower valves and tankless

  1. #1
    DIY Junior Member morpho's Avatar
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    Default shower valves and tankless

    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.

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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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.

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    DIY Junior Member morpho's Avatar
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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.

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    Retired Defense Industry Engineer jadnashua's Avatar
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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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member morpho's Avatar
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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!

  6. #6
    In the trades Dana's Avatar
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    Quote Originally Posted by cacher_chick View Post
    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.

  7. #7
    DIY Junior Member morpho's Avatar
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    Dana,

    Thanks for that insight.

    I wouldn't have cause to have it anywhere near that kind of temp as we don't have a tub and I like the shower at about 105-110.
    So I guess I'll try a thermostatic valve and see what's what.

    I came across these:
    http://www.deltafaucet.ca/bath/details/r10000-unbx.html
    which gives the option for different cartridge's

    Okay.

    Thanks again everyone.

  8. #8
    DIY Junior Member morpho's Avatar
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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

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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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.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Junior Member morpho's Avatar
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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.

  11. #11
    In the trades Dana's Avatar
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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.

  12. #12
    DIY Junior Member morpho's Avatar
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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.

  13. #13
    In the trades Dana's Avatar
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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.

  14. #14
    DIY Junior Member morpho's Avatar
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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.

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