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Thread: Navien Tankless Water Heater Comments and questions

  1. #181
    DIY Junior Member JimmyTony's Avatar
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    Hey Guys,
    Im getting ready to build a new house and was looking at in-floor heat using a tankless combined with a small tank to act as a "shock absorber" to keep the tankless, from cycling on all the time. In reading this thread I've come across some great posts by Dana and some others about this kind of system. I'm not a plumber, and could use some help getting a good mix of cost and efficiency in putting a system together. Any thoughts would be appreciated, Thanks!

  2. #182
    In the trades Dana's Avatar
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    This really should have been a new thread, eh? (It has nothing to do with Navien, other than that Navien doesn't void the warranty when their units are used for space heating.)

    Every reasonable heating system design starts with a good heat-loss estimate/calculation.

    If you build the radiant in to a concrete slab, it doesn't need a buffer tank.

    There are cheap ways of doing radiant with a tankless, but if your design condition water temp requirements are low enough, there may be better options.

    In climates as mild as Bend, for new construction, you have the option of spending the money on high efficiency building envelope rather than a high heating system. If you target design condition heat loads to be <<20KBTU/hr (not tough to hit for 2000-2800' house in Bend's climate, but it has to be designed), at which point you can have your cake and eat it too, since you can then heat & cool the place with a highly efficient ductless mini-split. (Even if it's not as cushy as radiant floors...) If you're not on a gas main and would be otherwise be using propane, it would be practically INSANE not to use an R410A refrigerant heat pump for primary heating in that climate. (If propane-fired radiant, even R410A air-to-water air source heat pumps start looking pretty good in terms of 10 year NPV compared to condensing propane, even though they're far more expensive than mini-splits.)

    Consider building to Zone-5 specs in the table 0.2 on p10 in this document, for starters:

    http://www.buildingscience.com/docum...-climate-zones

    Note that those R values are not center-cavity, but rather "whole wall" R with thermal bridging of the framing included. An R30 wall isn't a 2x10 studwall with R30 batts- when the thermal bridging of all framing is factored in that would come out at ~ R21-R22 for homes with "typical" or "average" framing fractions. But a 2x4" wall with R13 batts or spray cellulose + 3.25" of exterior polyisocyanurate rigid-board is ~R30, with typical framing fractions.

    Air infiltration is a LARGE factor in total heat load- designing a continuous primary air barrier on all 6 sides of the cube and having a Konstruction-Kommandant to enforce air sealing is critical, as is blower-door testing & remediation on the main shell as soon as you have the windows & doors installed. Typical pretty-good construction comes in at ~ 10 air changes per hour @ 50 pascals pressure (ACH/50), the standard leakage test. The IBC 2009 standard specs out 7 ACH/50 or less, which is usually achievable as a post-construction (read "post test-failure") retrofit. But to be very efficient you need to be under 3 ACH/50 and under 1.5 is better, and relatively easy to hit, if you have a plan and execute on it.

    Air sealing is by far the most cost-effective envelope performance upgrade you can do- a well insulated wind tunnel is a waste. Put a bead of caulk or acoustic sealant under & between stud-wall plates, foam seal & gasket foundation sills, caulk every sheet of structural sheathing to the studs, etc etc. It's cheap & quick, but it has to be consistent. On upper floor ceilings use OSB or ply on the underside of the joists/truss-chords (you'll need it to hold up the 20" of cellulose without bowing), and detail it similarly as an air barrier. Don't mess around with stuffing fiberglass in around window framing either- use the appropriate compliant foams.

    Only use insulated doors. Don't use sliding doors- they all leak like crazy with age (some even when new.) Swinging patio doors/french doors can be made to seal better. (But see notes about minimizing glazed area.)

    Minimize the total glazed area except where passive solar gains have been site-simulated and optimized. Every square foot of U-0.34 pretty-good window is an R3 hole in your R30 wall, with literally 10x the heat loss per square foot. Size & locate them for daylighting & egress needs.

    Use fixed (non-opening) windows where you don't absolutely need to open a window- they leak LOT less air. Where they must open, use casement & awning types, since they leak less air than double-hungs & sliders, and they give more egress & ventilation cross-section per square foot of glazing too.

    Avoid recessed lights, particularly those that would penetrate into attic or cathedral-ceilings. Even IC rated air-tight versions aren't usually all that air-tight, and make thin spots in the insulation.

    If taking the foam-clad framed building approach, a LOT of money can be saved by using reclaimed roofing insulation from commercial re-roofing jobs. An overcoat of R18-R24 iso or eps comes in at well under $5K for most reasonable-sized houses, which roughly triples the whole-wall R-value of a 2x4 fiber-insulated wall, and more than doubles that of a 2x6 wall. (If virgin stock it could easily hit $12K+.) Going to an air-tight R30 with glazing reduced to under 15% of floor area (as opposed to the ~18% new construction average) can cut the heat load of a house down to 1/3 or less of a typical-leakage typical glazing fraction code-min house, without having to live in dank darkness.

    To see what foam clad timber frame looks like, check out the retrofit the section titled "An architect works on his own house":

    http://www.greenbuildingadvisor.com/...builders-maine

    (Note the 1-part expanding foam in the pictures that seals the seams of his 6" of reclaimed iso board.)

    Other foam-cladding retrofits can be seen here: http://thousandhomechallenge.com/case-studies

    If you ARE on the natural gas grid, running low-temp radiant with a condensing water is roughly comparable to heating with a mini-split for a low-heat load house, but you pay quite a bit up front for that extra-cushy warmth underfoot. There's no payback on it, other than the "aahhhhhh" factor when it's 10F outside.

  3. #183
    DIY Junior Member JimmyTony's Avatar
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    Thanks for the reply Dana, and the info.
    I should provide more info. Radiant appeals to me because I can get it done in a slab for cheaper than a crawl space with a finished floor on it plus a separate heating system like a conventional forced air system. I know thats not the case for everyone, but it is for me. The ductless split is intrigueing but we have pets and allergy sensitive kids, so I was trying to take out the air movement from the equation. (dander and dust). Also, an aquantanace who had a split system installed says the moving air always feels a bit cold. Could be just her I guess. Also, I wanted to use the tankless for houshold water as well, so I thought thats where a buffer tank would come into play. i.e. prevent hand washing from forcing the tankless to kick on every time, not to mention the cold water sandwiches. As I say, I am not a plumber, but I'm trying to educate myself so I can make the best choice.
    Yes, an air tight envelope is part of the plan, likely a low density foam/ cellulose hybrid for starters, with major caulking, so I feel pretty good about starting with as reduced a demand as possible.
    We do not have the option of ntural gas, so propane or electricity are my options. I worry about the volatility of propane prices more than electricity prices in the NW, Propane is about $2.40/ gal and electricity is about $.10 /kwh which is about a wash before comparing efficiencies, but I also don't know if efficiency cclaims can be compared between propane units and electrical, and if they can be believed, especially heat pumps. I guess I've started to question all the assumptions I'd made while planning the house. I suppose thats good because I'm not locked into one idea/ solution/. But I need to come to a decision here pretty soon, and got to this site after my plumber laughed at my idea of doing infloor heat with electricity. He suggested propane and swears by Navien tankless. Thats the system he used with his in-floor system in the same neighborhood. What I've read here so far makes me lean more towards a Noritz or Rinnei, but obviously I'd have to committ to propane. The one thing I know for sure is that I don't know enough, so thanks again for the info and if you see a good heating solution somewhere in all this let me know.

  4. #184
    In the trades Dana's Avatar
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    Quote Originally Posted by JimmyTony View Post
    Thanks for the reply Dana, and the info.
    I should provide more info. Radiant appeals to me because I can get it done in a slab for cheaper than a crawl space with a finished floor on it plus a separate heating system like a conventional forced air system. I know thats not the case for everyone, but it is for me. The ductless split is intrigueing but we have pets and allergy sensitive kids, so I was trying to take out the air movement from the equation. (dander and dust). Also, an aquantanace who had a split system installed says the moving air always feels a bit cold. Could be just her I guess. Also, I wanted to use the tankless for houshold water as well, so I thought thats where a buffer tank would come into play. i.e. prevent hand washing from forcing the tankless to kick on every time, not to mention the cold water sandwiches. As I say, I am not a plumber, but I'm trying to educate myself so I can make the best choice.
    Yes, an air tight envelope is part of the plan, likely a low density foam/ cellulose hybrid for starters, with major caulking, so I feel pretty good about starting with as reduced a demand as possible.
    We do not have the option of ntural gas, so propane or electricity are my options. I worry about the volatility of propane prices more than electricity prices in the NW, Propane is about $2.40/ gal and electricity is about $.10 /kwh which is about a wash before comparing efficiencies, but I also don't know if efficiency cclaims can be compared between propane units and electrical, and if they can be believed, especially heat pumps. I guess I've started to question all the assumptions I'd made while planning the house. I suppose thats good because I'm not locked into one idea/ solution/. But I need to come to a decision here pretty soon, and got to this site after my plumber laughed at my idea of doing infloor heat with electricity. He suggested propane and swears by Navien tankless. Thats the system he used with his in-floor system in the same neighborhood. What I've read here so far makes me lean more towards a Noritz or Rinnei, but obviously I'd have to committ to propane. The one thing I know for sure is that I don't know enough, so thanks again for the info and if you see a good heating solution somewhere in all this let me know.
    With $2.40 propane as your fossil fuel and 10 cent electricity your heating cost will be at least 2.5x that of doing it with heat pumps.

    At $2.40 per 91000 BTUs and a 90% average burner efficiency that works out to about 10 cents/kwh, delivered- heat, but with a heat pump you'd most likely get a COP of 2.5 in winter, better than that in the shoulder seasons.

    With a continously variable interior unit the air movement issue is very slight (some use 2-speed AC motors, but the better Mitsubishis all use variable DC) and you can bump up the temps 2-3F for higher comfort and still be ahead. Placement of the interior units where they won't be blowing directly on you (at any speed) is also an important comfort factor.

    Ecotope (a consulting company in Seattle) has an ongoing study of primarily retrofit heat pumps all over the PNW commissioned by the BPA, some of which is available on online if you want to seek it out. You'll get a COP > 2.5 in Bend if you size it right, and at least 2 even if you don't.

    There's no particular cost-advantage to going with a propane tankless with a separate tank for HW compared to a condensing boiler + indirect. With a radiant slab and an even modestly high-R house your heating water temps on design day will never exceed 100F, and you'd need 120F+ for the tank.

    Design the house for the minimum heat load, THEN decide what mechanicals make the most sense. But there are 2-ton mini-splits heating high-R homes in much cooler climates than Bend, that cost less up front than a propane tankless + tank + radiant floor.

    With a Daikin Altherma air-to-hydronic heat pump and a low-temp slab you'd probably average a COP of ~3 in Bend, maybe even a bit more, but it'll be at least 2x the upfront cost of a mini-split.

  5. #185
    DIY Junior Member JimmyTony's Avatar
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    You mention combining a boiler and an indirect. Whats an indirect?

  6. #186
    In the trades Dana's Avatar
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    The coil inside the tank contains heating-system water, not mixing with the potable hot water. The indirect is usually operated as a separate heating zone, often a "priority" zone, inhibiting other heating zone calls until the hot water tank's call for heat is satisfied (that way you get 100% of the boiler's output applied to the hot water, much like a tankless.)

  7. #187
    DIY Junior Member JimmyTony's Avatar
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    Huh! Can you hook it up to a tankless (cheaper) instead of a boiler and have the tankless directly heat the floor, and the indirect supply the potable side? I don't know the efficiency of indirects but tmaybe this could be an economical choice as far as up front costs and monthly costs.

  8. #188
    In the trades Dana's Avatar
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    Quote Originally Posted by JimmyTony View Post
    Huh! Can you hook it up to a tankless (cheaper) instead of a boiler and have the tankless directly heat the floor, and the indirect supply the potable side? I don't know the efficiency of indirects but tmaybe this could be an economical choice as far as up front costs and monthly costs.
    In most states it's not legal (and not a great idea where it is) to run potable water through your heating system plumbing, especially at the volumes you have with a radiant slab, which is why you'd need the indirect. Tankless heaters aren't inherently set up and controlled for zoned space heating, and by the time you've monkeyed around engineering your way around it it's not clear there are any savings to be had. If the radiation water temp requirements are essentially the same as domestic hot water temps there are sometimes shortcuts, but with radiant slabs + domestic hot water you're talking dual-temp system. Condensing boilers can tweak double-digit savings out of higher single-temp solutions by using outdoor-reset curves to vary the boiler temp with heating load, resulting in more condensing hours. Navien and Rinnai both make combi-systems for both space heating & DHW with outdoor reset built in, but they're not particularly cheap either.

    And again, at Bend's average winter temps you'd pay less than half as much on space heating if you went with with an R410A refrigerant split-system heat pump solution, no matter HOW good your condensing propane system might be. From a strictly financial point of view you're far better off spending the money on insulation in a new-build not radiant heating, and heating with a (relatively)low cost but high-efficiency heat pump.

  9. #189
    General Engineering Contractor ballvalve's Avatar
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    I always plumb the radiant as a full time inlet to the water heater. Whats the beef? extra warm incoming water to the heater in the winter and removing heat from the slab in the summer. Seems like the best of both worlds.

  10. #190
    In the trades Dana's Avatar
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    Other than the fact that it doesn't meet code in most places?

    Using potable in the radiation is more corrosive to the heating system components (requires bronze pumps, etc.)

    Any zoned systems may have days/weeks/months of stagnation at tepid temps high enough to promote to potential human pathothens (protozoan & bacterial), which is the primary rationale for codes barring "open" systems. In MA open systems are allowed only if controlled in such a way to guarantee a specified minimum amount of circulation PER HOUR occurs whether the heating system is operating or not. In a tankless system recirculation this would usually cause an ignition cycle & burn, whether it's 95F outdoors or not.

  11. #191
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    Hi all,
    I have some questions of the external recirculating of NR240-A. I have a return line and I've set DIP switch 4/5 to OFF/ON and make sure the 3-way return valve is in the horizontal position. I set the timer to run about 16 hours. Is that all correct?

    I dont feel the return pipe getting hot.

    Another question, since I have the timer running 16hrs. What do I do if I'm on vacation? The tech told me to press the "POWER" button. I thought the "POWER" button on the remote is just for the remote keypad. Does it turn off the heater?

    After a power failure, beside setting the clock, what do I need to do to ensure the heater is on and running?

    Did anyone use a computer UPS with this heater, so heater will fire up during power outage?

    regards,
    C Lee

  12. #192
    DIY Junior Member Surfing Plumber's Avatar
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    Warning: Stay away from Navien!!!

    I installed a good amount of Navien in my life time and I gotta say, 80% call backs from my customers. It is frustrating for both the homeowners and I as it takes time away from my other jobs!!

    There is always something wrong with these Navien, if it's not the flow sensor, it is the mother board.. I am tired of them...Stay away. go for other reputable brands like Noritz or Rinnai

  13. #193
    DIY Junior Member Tankless Adviser's Avatar
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    Default Hmm...4% difference in efficiency eh?

    Quote Originally Posted by nhmaster View Post
    sorry, I didn't catch that part. But going through your pas posts I really couldn't find a compelling reason other than the great price you got on the unit. That is in itself reason for question since even with my discount I can't buy one for that. Aside from that though, How far did you have to run the stainless steel vent pipe up through the roof because that stuff ain't cheap either. Oh and while we are at it, did you check the maximum allowable length of the vertical vent pipe. Because those darned things can and will condensate on long runs, especially if the pipe passes through a cold attic. probably nothing to worry about though.

    Maybe it seems like I and others are dissing you or having sport with you and nothing could be further from the truth. What we are trying do do is educate a public that has been hypnotized into buying this line of efficiency and economy that just flat does not exist. The math is the math. People lie. Numbers do not. So other than the one in a lifetime price you got on the unit, and your ability to self install it (and btw I looked at your pictures and you did a nice job there) why would anyone consider installing one of these. Please don't give us the line about a tank type running all day long when you are not hoem because they don't. If they did the operational cost differential would be much greater than it is, and that runs about 4% normally. 4% projected over 10 or 20 years does not make up for the cost and service.


    Hi nhmaster,

    You claim that tankless water heaters are only 4% more efficient compared with tank type water heaters. Could you provide us your source? From what I understand, even the best insulated tank water heaters have efficiency ratings in the 67% energy factor range. Now add condensing to the tank and you are still below 80%. If you believe this to be wrong information, perhaps you should visit any tank water heater manufacturer's website and look at their efficinecy ratings.

    By the way, a condensing direct vent tank water heater costs more than a condensing direct vent tankless water heater. You said you are in the business, so you should know this. You should also know that nearly every tank manufacture today has gone out and secured a tankless OEM line for themselves. If the technology was not proven, they would not waste their time, energy, or efforts with tankless technology.

  14. #194
    DIY Junior Member Tankless Adviser's Avatar
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    Quote Originally Posted by ChuckS View Post
    I would like to throw the unit I have into the mix. We have the Paloma 7.4 and so far it's solid. It also has a duel flame burner, very stable temp output and did cut our energy bills way down.

    http://www.tanklesswaterheaters.com/waiwelaph28ri.html

    I agree my wife and daughter take longer showers but that doesn't negate not heating water through the day and overnight. Not to mention if you go away for the weekend etc... Will it pay for itself is another question all together since ours was $2600 installed but I will say we're very happy with it and I don't miss running out of hot water in the mornings (I am the last in the shower).

    I do not believe that you Paloma unit has a dual flame burner. As of the time of this email, Noritz is the only water heater with a Dual flame burner. They also have an eco burner on their new line of products. By the way, Rinnai is also up there in terms of quality, but I would have to say Noritz is the best of all tankless water heaters. They give you products specific to your needs, so you can definitely find one that suits your needs at a good price.

  15. #195
    DIY Junior Member Tankless Adviser's Avatar
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    Quote Originally Posted by Scott D. Plumber View Post
    At one time the Wright Flier was a “Fad”, Henry Ford was wasting his time with motor cars and copper pipe was for amateurs who could not cut and thread Galvanized. Everything happens in stages and the first stages are more expensive…at first. Remember the first flat screen TV’s?

    The Consumer report piece is so obviously a hit piece it’s not funny. One day, I’ll take the time to go through it and blow it up, but not today.

    As for Navien, it’s an ok product but plagued by temperature swings at low temp rises. It makes a better boiler than a water heater IMHO. Rinnai is my favorite with Noritz a close second. You might think you are saving $200 in vent with PVC but the unit cost $200-$300 more than a comparable Rinnai and then you have to cut/prime/glue the ugly PVC. Unlike the low profile, single concentric, push-joint Rinnai vent. So what have you gained? Plus the Rinnai gives more hot water and so does Noritz.

    The Navien is 90+ Really? If I have a car that gets 50mpg and a car that gets 38mpg in the driveway, and they are both “OFF” which ones is getting better mileage? We are talking about equipment that only runs for a fraction of the day anyway. I would think actual energy difference is negligible.

    That said, the there is only one product with a nationwide network of trained Authorized Service Providers, a 24/7/365 tech support (in the USA, Not India) and a highly trained Rep network. That’s Rinnai. Nothings perfect, but some things are better than others.
    I am suprised that you prefer Rinnai over Noritz. If you want to speak about ease of installation, the Noritz concentric vent products are easier to install than Rinnai. No cutting of venting required and no gluing required unlike the Rinnai concentric. Also don't fortget the 25% thicker heat exchanger that will increase product life by 25% compared to Rinnai. We haven't even started on the dual flame burner that helps out with heat exchanger longevity due to more evenly dispersed heat intensity in the combustion chamber.

    I can't help it; I just love the Noritz product line and I am sure that based on my previous posts, you are probably aware that I am pro Noritz. This is a company that has the best of both worlds. Concentric venting for our non-condensing units and PVC636 venting for our condensing units. No matter what your application, you definitely have a product that will work for you. By the way, Noritz went with PVC 636 venting for their condensing units so that you don't have to spend so much more on venting if you have to snorkel due to inadequate clearance of the vent termination to grade.

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