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Thread: Tankless the only option? - MultiHead Shower

  1. #16

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    Hi Sam,

    I want to power one over-the-top shower with hot water long enough for my wife and I to take showers one after the other.

    That shower has:
    4 x 2.5GPM body sprays (Kohler water tiles)
    1 x 2.5GPM Shower Head
    1 x 2.5GPM Hand shower.

    Only one of the two hand shower or shower head needs to be on at any given time. So a total of 12.5GPM.
    For this experience, I do not want to worry about not having enough water pressure or having cold bursts of water intermingled with my shower, especially having a cold burst because someone else in the house does something as simple as turning on a faucet.

    I would prefer to be able to take a standard shower (non-body spray) and do laundry, run a dishwasher, or have another person taking a shower elsewhere and experience no ill effects.

    Tanks are not out of the question, though by my math a 90 Gallon tank at 75% mix will only get a single 12min shower or so.

    Our current water heater is in our attic (Texas style). My wife is not a big fan of having mega gallons of water in our attic due to paranoia over a leak or spill (bad experience).

    My water temp this time of year is 60-65F. My water pressure at the faucet outside is 55-65PSI. This leads me to the 60F rise (60->120) that I use to look at all of the GPM data on the tankless units.

  2. #17
    Geologist sjsmithjr's Avatar
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    I keep having to turn my computer over to the IT guys so pardon the brevity of my posts. A single 100 gallon Bradford White EF100t (commercial) has a first hour delivery capacity of 569 gallons at 60F rise, a recovery rate of 499 GPH, and a 3 hour average of 523 GPH and is supplied by a 3/4 inch gas line and requires a 3 or 4-inch vent. That's overkill, of course, but the point is there's more than one way to skin a cat if all your looking for is back to back over the top showers. Also consider that the use of tempering valve will extend the first hour delivery capacity of a more modest water heater.
    Last edited by sjsmithjr; 02-23-2009 at 05:42 PM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  3. #18
    Illinois Licensed Plumber SewerRatz's Avatar
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    The tankless units I like that are similar to the hybrid heaters is the Navien Tankless "A" Models they have a built in recirculation pump and a mini buffer tank. Duel stainless heat exchangers, PVC venting 98% efficiency.

    The remote control has a built in recirculation timer too. here is the brochure http://america.navien.com/PDS/ftp/Na...8_Brochure.pdf

    and here is the web site for more information. http://www.navienamerica.com/

    These units really impressed me when I seen them installed and at the trade shows. The built in recirculation pump has the ability to recirculate the water with in itself, to help eliminate the "cold-water sandwich" if you do not have the piping available for external recirculation.http://america.navien.com/KD_eng/internal.html
    Last edited by SewerRatz; 02-24-2009 at 05:53 AM.

  4. #19

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    So I went and got quotes on hybrid systems as well.

    The cost I have for 2 x R94Lsi Rinnai's + Recirc system (includes 12 Gallon electric tank) 30% cheaper than a Single GU32 system with recirc installed.

    Given the cost, I think I'm going to end up doing the Rinnai's. I'll figure I'll have to spend maintenance for flushing once a year, replacement of recirc tank every 4 years or so. Even with that, the Rennai is going to be cheaper.

    <crossing my fingers>

  5. #20
    DIY Member dimprov's Avatar
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    Nicholas,

    With those facts and choices, it seems like a no brainer, provided you have the space. Consider:
    1. You would need to maintain the GU32 as well.
    2. Odds are against both Rinnai's failing simultaneously. So, if one goes bad, you still have one to limp along on until you can repair/replace the broken unit.
    3. If your recirc tank goes bad, it's easy and cheap to replace. Should be DIY simple. What brand and model recirc tank are you planning to use?

    I'm gravitating toward a similar design, but probably involving 3 tankless units in parallel instead of two, provided the minimum flow rate does not increase by 3x. I would guess the manifold controller lights up one tankless unit until the flow rate is 2x or 3x the minimum, at which point it would light up the second and third unit respectively and then load balance thereafter. Not sure if I'll use Rinnai or a tankless (still to be identified) whose heat exchanger enables the pottable water to be physically isolated from the hot water being recirculated through my hydronic heating system.

    As an aside, the tax rebates on solar are looking pretty good right now (even with installation, I'm told it's almost zero net cost), so I might add that into the mix. Since you're in Texas, you might want to consider it as an add-on also. It was actually the Rinnai dealer who was trying to sell me on solar.

    David
    Last edited by dimprov; 03-03-2009 at 12:31 PM.

  6. #21
    DIY Member dimprov's Avatar
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    It shouldn't change your decision, but one possible gotcha I just realized: somewhere down the line one of your units goes bad and needs to be replaced. Not a problem now, but in the future maybe that model is no longer made. What then? Will the tandem/manifold controller work with a mix of different units? Or does the controller become the weak link that forces you to replace *all* your units? Ouch.

    Any precedents, based on earlier models that are now "obsolete" and no longer being manufactured?

    David
    Last edited by dimprov; 03-03-2009 at 07:03 PM.

  7. #22

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    Well, I have the units installed.
    2 x R94LSi units in parallel with a 12-Gallon electric tank and Grundfos Recirc pump (retrofit style) hooked up. It's working ok so far. We'll so how it does one I get the shower in.

    I had just one unit hooked up for a day, and turned on 5 faucets and a standard show head and saw the pressure downstairs fall enormously (my method of guessing at water pressure lost once I get my shower system installed). I'll try it today when I get a chance with the two units.

    Question: Are you better off lowering the temp for both units and using less cold water mix or increasing the temp for both units and mixing more cold for pressure?

  8. #23
    Retired Defense Industry Engineer jadnashua's Avatar
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    Probably running them hot and using less. Safety needs to be considered here as well - there's both a practical and safety limit on how hot the supply should be. Do you have a tempering valve at the outlet of the tankless systems?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #24

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    I would doubt I have a tempering valve, as I don't know what that is.
    I can control my tankless temps via remote, so I could only turn it up before showering.

    I will have a thermostatic valve at my shower, which I believe will keep me from getting boiled.

  10. #25
    Retired Defense Industry Engineer jadnashua's Avatar
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    Unless that is the only user of that hot water, anyone using hot could be at danger.

    Basically, a tempering valve is used to set a maximum output temperature; if the hot inlet is above the set point, it mixes in some cold to 'temper' the output to the desired maximum, fixed level. They're required in some places, and you may actually have one. Some tankless manufacturers also require them, depending on design.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #26
    DIY Member dimprov's Avatar
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    Just how accurate are tempering valves? Is it +/- 1 degree, +/- 5 degrees, +/- 10 degrees, or +/- 20 degrees?

    I read that they are somewhat crude and can have large +/- temp variation, but I couldn't find any info beyond that. It would force you to set the water temp low enough so that the largest possible high-side variation won't scald you.

    David

  12. #27

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    We are putting in a shower system similar to your set up Nicholas_ii. Do you have your shower in yet? Just wondering how your setup is working....

  13. #28
    DIY Junior Member snd1232's Avatar
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    Default twin water heaters

    I just wanted to comment that we have a MAAX shower with 8 in-wall heads plus an overhead and sprayer plus an additional 2.5 gpm shower head for a total of 10 heads working at any one time. Total waterflow is estimated at up to 20gpm. We have twin 9gpm ranni heaters all plumbed with 1-inch lines and we have never run out of hot water or had pressure issues, inspite of running off well water.




    Quote Originally Posted by Nicholas_ii View Post
    Would you expect that I would still have hot water pressure issues with 2 9.4GPM units? Practically, I don't think I would ever use more than 10, maybe 12.5.

    There's no data for how 2 units in tandem work together.

    It's a also a bit unclear how the recirculating system will play into affect here.

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