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Thread: Navien Tankless Water Heater Comments and questions

  1. #151
    In the trades Dana's Avatar
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    As I understand it, when the burner modulation has already hit the max rate, flow control restricts the flow to maintain the output temp at or near the thermostatic setopoint. Without flow control the output temp might otherwise drop at high-flow, high delta-T. In practical terms that's not very important for gas-fired units in warm-water states like GA, but if you're trying to fill a tub in MN in January with 35F incoming water, maintaining a high enough output temp without flow control might be more critical even with a 199kbtu burner behind it.

    In GA that would almost never be necessary with any "whole house" gas-fired unit, but would be with an electric tankless since their ratings are so much lower. A 24kw electric tankless is roughly equivalent to a (fairly light-duty) 100KBTU/hr gas tankless, and even in GA the ol' lady would outright kill ya if you decide to start the washer while she was in the shower in January with a 12 or 15kw unit, without flow control (and a functioning anti-scald valve.) But a 36kw unit would probably support two shower flows in GA without needing to throttle back on flow to keep temps up.

  2. #152
    DIY Junior Member Abraham's Avatar
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    Thanks much Dana, but I'm afraid uch of that flew over my confused head...

    If I understand correctly, the "flow control" feature that many of these units tote is essentially a flow restrictor? And if thats the case why would the flow be restricted? Is it b/c the unit wishes to guard against the possibility of another tap or two being drawn at the same time? And why would this be designed to occur only when the "burner modulation" hits the max?

  3. #153
    Retired Defense Industry Engineer jadnashua's Avatar
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    Move you hand through a flame...move it faster, things are cooler...slow it down, they get hotter. Now, change that to a blowtorch, if you go through it fast enough, you won't get burned. Now, replace your hand with water going through the burner. Two ways to get the water to a fixed temp...how fast you move it by the burner, or how hot the burner is. If the water is cold coming in, the burner might not be able to supply enough heat if you are trying to run that water by fast (i.e., using lots of water). So, having both the ability to adjust the burner and slow it down, if trying to use lots, are two methods that will allow the thing to output a fixed temperature.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #154
    DIY Junior Member Abraham's Avatar
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    Thanks for the additional clarification Jadnashua... So essentially this "flow control" feature that these marketers promote is merely a mechanism to guarentee that the hot water temp doesnt suddenly drop due to a sudden increase in demand or colder incoming water temps (hence the reference to Delta T that Dana made earlier).

    Yea Dana you almost lost me with that one (Delta T) but then I used the magical Google tool...

  5. #155
    In the trades Dana's Avatar
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    Sorry- I live in the nerd-world, where expressions like "delta-T" are practically small-talk. (Note to self: define your terms- always.)

  6. #156
    DIY Junior Member G WASH's Avatar
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    Where are you going to use the unit? Will there be a water softner and filter's preping the incoming water supply. See my perspective is different than many here. I own carwashes and I make a living off of the end result...HOT water. Over the year's I've tryed nearly every form of hot water production. And I know thru discussion with other owner's of washes and related industries "What has worked and what sounded like it should work". It's obvious that the condensing unit's are much higher in eff. The deal as I see it is as alway's value over time and cost when it's all said and done. The price on the Navien 240's is right at 2,000$ unit only. Track record...a realy short one. If it's for a large home or small business of mine I would go with what I KNOW... The Takagi TK3 Pro is the staring point of thier commercial line. I have seem their prices dropping over the last 2 year's. I picked up a TK3 for 725$ and the higher tech/more durable burner TK3 pro for 900$ Most good Carwashes use commercial grade softner and filter's that are over kill so as to make the process of producing spot-free rinse water easier and less costly in the end...As a result this make an already highly reliable TLHWH last a long,long time. All the wash owner's I've asked said they had never had the front panel's off their TK2,3's and up. I personally have had mine for 7 year's plus...no repair's The other wash owner's tell the same story. Takagi commercial line is a work horse at a busy carwash...should last 20 year's in a home and at those prices I think i'll wait to see if the Kia..of sorry Navien from Korea can walk the walk In a heavy use areana. The 1100$ price difference will buy a lot of natural Gas...Sorry I hate spell checking so you get my drift

  7. #157
    DIY Junior Member ImpliedConsent's Avatar
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    Hola... like others, google search brings up this thread near the top, so kinda resurrecting. Abraham can probably tell you more about code (I live in the Atlanta area too), but I went with Navien NR-210A because of the costs and research.

    1) house was built in 1993, fist owner. It still has the original A.O. Smith 40gal HWH tank. I've NEVER serviced it and barely even glance at it; however, 17yrs old got me to do some research. First, my bet is that the bottom will dump soon. It's isolated, so I don't believe much damage will happen. Second, it's terribly inefficient by todays standards. I run out of hot water quicker and it takes awhile to get any back. Since it was built in 1993, the codes were different. For me to install a new tank HWH would require the company to install a square cement wall around the unit and deepen the ditch (it's in a "half" crawl space with 6' height). The existing unit is 48" and newer units are taller. BLUF: to replace with a .7EF HWH, 12yr warranty, do the install with construction will cost me about 3k and no 30% Fed Credit.

    2) for 3.3k, I get a new Navien NR-210A (bells/whistles), .98EF and installation of circulation T's at the long runs on external circulation, 15/5yrs warranty ... and the 30% Fed Credit. To me it was no brainer. More efficiency, less cost overall after credit.

    My math:
    Standard tank: 3000.00
    Tax Credit: 0.00
    TOTAL: 3000.00

    Tankless: 3300.00
    Tax Credit: 990.00
    TOTAL: 2310.00

    Delta: 690.00 savings going tankless, + reduced gas costs.

    Anyone see anything wrong with my math?

  8. #158
    Forum Admin, Expert Plumber Terry's Avatar
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    If making all of those changes will run $3,000 for a tank type heater, then you might as well go tankless.
    If the tank had been in a garage, then replacement with a new tank and expansion tank would have been less the $1200
    Depending on the market, maybe even less then that.

  9. #159
    In the trades Dana's Avatar
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    It's usually hard to make an economic argument for going tankless if it's based on fuel savings alone. But this one sounds like a no-brainer, even if you add in some service charges for mainentance over the next decade or so. And just thing, you'll be able to waste as much hot water as effieciently as you like with an EF of 0.98! :-) (Have any long-showering teenagers in the house?)

  10. #160
    DIY Junior Member ImpliedConsent's Avatar
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    Quote Originally Posted by Terry View Post
    If making all of those changes will run $3,000 for a tank type heater, then you might as well go tankless.
    If the tank had been in a garage, then replacement with a new tank and expansion tank would have been less the $1200
    Depending on the market, maybe even less then that.
    Well, I certainly didn't think that I'd get a response from "the man", but there it is. Believe me, I'm envious of seeing HWH's in the garage, but mine is in our basement's 1/2 crawl space. It's convenient on one hand, I never see it; however in times like this, it's a burden. I've had 3 companies come out and they won't touch it without the modifications. My 3k quote was the low quote (I won't even suggest what the others were). From all the research I did, the Nevien consistently hit the top of the charts as it relates to EF and warranty (my 2 criteria). I provided each company with my research. I got responses from my research: from dumbfounded - never heard of companies like Navian or Noritz or Paloma ... to stunned happy surprise that a consumer did research. Needless to say, the Navien won out. My research was done not on company market fluff, but the governments Energy Star program. As of right now, there are ZERO tank HWH's that qualify for the credit.

  11. #161
    DIY Junior Member ImpliedConsent's Avatar
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    Quote Originally Posted by Dana View Post
    It's usually hard to make an economic argument for going tankless if it's based on fuel savings alone. But this one sounds like a no-brainer, even if you add in some service charges for mainentance over the next decade or so. And just thing, you'll be able to waste as much hot water as effieciently as you like with an EF of 0.98! :-) (Have any long-showering teenagers in the house?)
    OMG: 13yr old who thinks water is unlimited resource for her showers is an understatement. She is effectively training my 7yrs old daughter those same habits. I would say that my wife is the master of giving me cold showers, but I think she lurks here. I'm in the military, so taking a hot shower is a luxury anyway, so I'm used to it.

  12. #162
    DIY Junior Member ImpliedConsent's Avatar
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    One more thing (before I become a pain in the @$$): just found out that I also qualify for my states Energy rebate program, which is another 199.00. Total savings: 889.00

  13. #163
    In the trades Dana's Avatar
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    Quote Originally Posted by ImpliedConsent View Post
    OMG: 13yr old who thinks water is unlimited resource for her showers is an understatement. She is effectively training my 7yrs old daughter those same habits. I would say that my wife is the master of giving me cold showers, but I think she lurks here. I'm in the military, so taking a hot shower is a luxury anyway, so I'm used to it.
    Is there enough headroom in the crawl to install even a 30" drainwater heat recovery heat exchanger vertically in a drain down stream from the shower? SFAIK there's no subsidy for them in GA, but it'll boost the "apparent efficiency" of a condensing Navien into the 130-140% range during showers, reducing the water heating bill for the kids. (It's a few hundred bucks if you buy them wholesale.) It may be slow to pay off if your gas prices are low and you're running a Navien, but it's pretty quick for propane-fired water heating.

    OTOH, if you used an occupancy sensor switch for the bathroom lights and set it up to time out in 5 or 6 minutes (8 min, if you're feeling generous or your wife objects) you might be able to re-train them to take shorter showers, for less than $50 in hardware costs, eh? ;-) (I have both the drainwater heat recovery and occupancy-sensor light switch going to keep my 10 year old reined in, or from having to listen to my wife's opionions about the lack of hot water through the closed bathroom door.)
    Last edited by Dana; 11-04-2010 at 01:55 PM.

  14. #164
    DIY Junior Member ImpliedConsent's Avatar
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    Thought I'd share install pictures The new tankless is in nearly the same spot as the tank.
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  15. #165
    DIY Junior Member ImpliedConsent's Avatar
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    Err... now that I look at Navien's fluff marketing, I'm concerned that my install wasn't actually complete. Can y'all tell me how I should resolve this? The quote was for external circulation.
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