Navien Tankless Water Heater Comments and questions

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Dana

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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.

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.
 

Dana

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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.)
 

JimmyTony

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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.
 

Dana

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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.

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.
 

Ballvalve

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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.
 

Dana

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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.
 

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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
 

Surfing Plumber

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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
 

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Hmm...4% difference in efficiency eh?

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.
 

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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.
 

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At one time the Wright Flier was a “Fadâ€, 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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:):):):)

Yeah, I too get a bit of a laugh out of the "98% thermal efficiency" numbers for Naviens, in much the same way that I do with the overzealous mod-con boiler advocates.

An on-demand hot -water heater almost BY DEFINITION short-cycles on most of it's burns. Anything less than 5 gallons would be an efficiency-robbing short-cycle for tankless, condensing or otherwise, and even though the bulk of the water use is indeed bathing/shower draws greater than 5 gallons, the numbers of short-cycles, the fixed-losses per burn (flue purges & ignition sequences) add up- they aren't anything LIKE 98% efficient, or even 90% in real-world situations, no matter what their EF number is. (An EF test takes 10+ gallons at every draw, enough to signficantly inflate the performance of a condensing tankless.)

What determines the real as-used efficiency is how well the unit manages the fixed losses on short-draws of 2 gallons or less, not whether it's condensing/non-condensing. Depending on real world use patterns and the fraction of large/small volume draws, a non-condensing tankless will run anywhere from 75-80% efficiency, whereas a condensing unit might run 75-85%, no more.

Used as a condensing space-heating boiler a condensing tankless can indeed hit 90%+, but only if the return water entering the tankless is below 110F. In order to hit 98% the return water would have to be under 70F. While not-too-likely in a heating system, 98% efficiency possible for high volume hot-water draws, since the water from street is typically well below 70F. But the average efficiency as a hot-water heater will always be considerably lower than it's steady-state thermal efficiency.

Tankless HW heaters see a huge number of ignition & flue-purge cycles, robbing efficiency as well as wearing out some of the sub-systems. Even a small well-insulated buffer tank can cut the number cycles by more than half and increase the overall efficiency (while getting rid of the "cold-water sandwich" issue) for the efficiency cost of a small standby loss (less than 1%). From a fuel-saving point of view it's not always cost-effective for just water-heating, but in a combi space-heating/DHW system it can be. (Systems using a reverse-indirect like a ThermoMax or ErgoMax as a heating system buffer while acting as a DHW heat exchanger tends to work well for homes with low/moderate design-day heat loads of 25-75KBTU/hour. But if it's an already high mass low temp radiant-slab heating system where lower than 110F temp heating water is typical the reverse-indirect-as-buffer approach is less than ideal.)

The best selling point for a condensing tankless is when it can use a cheap PVC vent stack instead of stainless/Z-vent for the standard-efficiency model. In installations with long vent runs the installed cost of a condensing tankless + PVC vent sometimes works out to about the same or less than a standard-efficiency unit + Z-vent. In those cases taking the (very modest) efficiency savings offered by the condensing unit seems fair.


By the way, the Center for Energy and Efficinecy has a report out that states that none condensing tankless water heaters performed at highere efficiencies under low flow conditions than Navien condensing tankless water heaters with Buffer tanks. Keep in mind that none condesning units are rated in the mid 80% efficiency range.
 

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JM, a few thoughts to ponder:

How many Rinnai's do you install per year? Does not the Rinnai have better water temperature control and higher flow rates? Doesn't it cost a couple hundred bucks less and have better tech support?

For efficeincy, if you have a car that gets 30mpg and one that gets 35mpg, and they are both in the driveway "OFF" which one is getting better milage?

Now I get the PVC vent thing, however if the venting is up and out the Rinnai is still less expensive with an easy push joint vent kit and a much better hot water source. These things only run for minutes a day, the rest of the time they are off. I think 90+ is over rated for tankless. Seems to me that tgemperature control and flowrate matter more.


Agreed that temperature control and flow rate are both more important. But which tankless provides both features better than any other manufacturer does? according to the Center for Energy and the Environment, Noritz wins on both counts. Don't get me wrong, Rinnai is a very good unit, but I still like Noritz better. Navien has made some improvements to their water heaters over time, but they are still nowhere near the Japanese manufactures such as Rinnai, Takagi (now AO Smith), or Noritz. As for me, I will stick with Noritz any day.
 

techsavy

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80+ is (quite literally) overrated for most tankless in most installations due to the particulars of the EF test: 10.2 gallon minimum draws are nothing like real-world use, and the short-cycle losses for sub-2 gallon draws erodes efficiency dramatically. In real-world draw profiles 0.82EF type tankless units hit in the mid-70s, condensing versions scoring 0.90+ EF numbers run in the high-70s/low 80s. The higher thermal efficiency isn't worth (much) extra for. (Indeed, you'd get better return in fuel savings on drainwater heat recovery on the main shower for the price-delta on the high/mid efficiency units themselves, vent costs not included.)

Steady-state thermal efficiency is a theoretical upper limit, but not a good measure of the real-world performance. Those with tight controls over flue purge cycles losses will do better than those that don't. Those with small header tanks to mitigate cold water sandwich issues that also inhibit fire when the header is above a minimum temp will also suffer fewer cycles, and thus lower purge-losses from multiple low-volume draws, etc. Steady state thermal efficiency or raw combustion-efficiency numbers are only relevant for very large or continuous-draw duty (pool heating, anyone?), not domestic hot water for typical household use. In space heating, commercial laundry/car-wash, health-club showers, or home solar-backup you might beat 90% with a condensing tankless, but not very often (if ever) in straight-ahead DHW apps.


BTW: A a question for any of you who have taken (or will take) the tech courses from various tankless vendors: Is there a modulation level where they typically peak out on raw combustion/thermal efficiency? Do any vendors share any of that data?

Condensing versions likely peak at lower fire in 25-35% of full-fire range (like most mod-con boilers), but I suspect the single heat exchanger types may do better at the high range (like copper-tube boilers), and may be under 80% for raw combustion efficiency at the low end of the modulation range, but 85%+ in the mid/high range. I could as-easily believe the designs have been tweaked to provide peak efficiency at some other burn level, but haven't been able to find test data (which I'm sure is quite proprietary when tested by the manufacturers). Can anybody either confirm/disabuse me of those guesstimates?


I have not personally done any tests, but it looks to me that the efficiency depends on temperature set-point as much as it does on length of usage and firing rate. You would have to look at the effects of temperature set point and of firing rate vs. heat exchanger longevity to identify the optimum usage factors. This of course is not easy to determine. I would immagine that it is not advisable to operate a water heater at the low firing rates for too long or to operate at maximum fire for too long either. Somewhere above 50% burner burn should in my openion be a target range, since all burners will be activated and hence the heat distribution in the combustion chamber would be better thermal control of the heat exchanger pipe coils.
 

techsavy

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I'm going to add to this topic again. when they first hit our local central california coast market, I liked them but the problem of low flow cut out became a problem and changing boards became a regular task for us. What did become a problem was the issue remained after the 1 year labor ran out and Navien would not honor replacement of known problems with these by paying to have these replaced.
Considering the near non response of the sales distributor and the full mailbox of tech support on weekends, I wouldn't recommend this line for any reason. The recirculation pump feature in the A models can not be set up with a remote on demand feature and the pump has limited head capability. I challenged the sales rep how 98% efficiency is achieved with temps at 120 or lower at low flows, he couldn't answer that and has quite touting this at trainings.
We've been installing tankless for over 30 years and have seen our share of what works and what does not. Navien has failed to realize service makes or breaks a company and in my book they lay near at the bottom with Bosch.


Where do the others rank in your book? Who is at the top of the crop?
 

techsavy

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Tankless testing (all brands) follow a standard testing procedure for determination of combustion efficiency and EF.
10 Code of Federal Regulations Section 430.23.
In a nutshell its a series of draws at different flow rates and gallons.

So if Navien is misstating efficiency so is all others.

I wont argue about what it takes to get to it, yes it involves cooler inlet water, but so do the 80%ers to achieve 82-84%.

Whats the big deal with changing a part, make it part of the charged annual service


Actually, you are not very accurate here. Yes, tankless tests are all done in the same manner, which means that Navian's A models are tested in the same fashion as the competitor's brands without a buffer tank. It also means that the Navien A model is tested without the pump in operation, so the advertised efficiency is actually quite a far cry from what it actually delivers in real life tests. You should take a look at the study done at the Centre for Energy and the Environment. According to that study, at below 100000 BTUH per day usage, the Navian A models are actually worse than non-condensing models which are rated with efficiencies in the low to mid 80% range.
 

techsavy

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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.


This is actually not the way to go about this. Your tankless is not a boiler and therefore cannot be used in the manner described. Your tankless must heat domestic water directly. You can add a heat exchanger to heat the space indirectly, but keep in mind that there are rules guiding how much space heating can be done using a water heater. see the following link http://www.noritz.com/u/plumbing_diagrams/nr83/7a1_nr83_dhw_rad.pdf
 

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in the spring i helped remove an old corroded boiler from a house with about 12 bedrooms and 4 bathrooms. the boiler and 2 water heaters supplied DHW and radiant heat. we
replaced it with a Takagi tankless to run the DHW for the summer months with the intentions of plumbing it for radiant heat before winter. Well, the home owner found a Navien
CH240 to do the job instead. I have to say that i liked the Takagi. It installed easy and did provide almost instant hot water, and was simple to operate. We are however
experiencing problems with the Navien. It keeps giving us error codes for low pressure just running one sink for less than 2 minutes, and we can't adjust for elevation with a dip
switch like the Takagi. I have read about 2 years worth of posts on this subject and frankly i have some mixed emotions on the whole tankless concept. Anyone have any
suggestions?
 

Dana

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Tankless Adviser: Firing rate is only a secondary factor on the raw combustion efficiency, and setpoint temp is third-order factor for tankless units. Incoming water temp is primary, and it's ALWAYS going to be well into the condensing range in DHW mode, but can be much warmer/less efficient in space heating applications with high return-water temps.

In DHW mode whether it's at min-mod or full-fire a condensing tankless will always be north of 95% steady-state, whether the output temp is set to 40C or if it's set to 60C. There will always be condensing going on in part of the heat exchanger that contains water under 50C. But flue purges on short-draws eat into efficiency considerably, since every purge extracts the same amount of heat out of the the heat exchanger whether you just took a 20 minute shower, or whether you just rinsed your hands. On the former that loss is a negligible fraction, on the latter it's a good chunk of the total burn. The US DOE EF test over-rates tankless units relative to tanks, since the use profile is all long draws.

I'm curious about the test data on the mini-buffered Naviens- is that Centre for Energy and the Environment available online?
 
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