Concerned with reliability of tankless options

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jetto-setto

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Hey guys, new here. I've got the opportunity to replace a standard tank-style water heater with a tankless unit. I've done a lot of research, but still have some questions. My first real encounter with tankless heaters was on a stay in Japan, where I was fascinated by the multi-room remote controls, temperature fine-tuning, and even automatic tub-filling. My friend's house had a Rinnai, but I certainly don't have any reason to favor that brand.

In terms of the idea of tankless, I'm sold. But I'll admit, I've been a little put off by the number of complaints online for even the big brands like Rinnai/Noritz with regards to the reliability of the units (perhaps Noritz especially). Although I understand that tankless units may require more maintenance - and that's fine by me - but I wouldn't want something that's just a complicated nightmare compared to a simple tank, especially given the higher cost.

Any advice on this would be greatly appreciated. Are tankless units more problematic than simple old tank heaters, or are the complaints online more to do with the fact that people are more likely to post about their problems online than their successes? Which brands, if any, are generally considered to be the most reliable? Thanks in advance!
 
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Dana

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Tankless HW heaters have peak flow issues and maintenance issues, but properly installed and properly attended to they'll last a coupla decades. A common installation error leading to flaky performance (or worse) is insufficient gas distribution plumbing &/or insufficient gas meter/regulator size for a bigassed burner like a tankless. It can be expensive to do it right.

Rinnai is the world's largest manufacturer of gas burning appliances, with very good design and distribution support, but that's not to say you can't do as well with some of the others.

There is no good financial rationale for a tankless at current US natural gas prices, but there can be with propane. Efficiency wise you can do as-well or even better with a condensing tank hot water heater, and a tank will fill a tub faster than a tankless, since it's flow is not burner-capacity limited. But a tankless buys you a few feet of living space (a major factor in Japan, where they are usually mounted outdoors.) In US-sized houses that's not as important, but still some. In the US I've seen them wall-mounted above the washing machine in tight quarters to avoid eating into valuable usable floor area.
 

BadgerBoilerMN

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We have installed most of the gas-fired tankless water heater, both condensing and non-condensing, over the last 25 years, starting with Bosch and Aquastar/Polaris. Proper application, installation and maintenance are the key to performance, reliability and longevity. They are particularly well-suited to warm climates since ground water temperature dramatically effects output.

All must be fed soft water. Note the period.

We currently install Bosch, Takagi and Navien with great success. We have great support and experience, which is what you want in your local market. DIY online reviews are of little use the the layman so local supply and support are important even if you install the unit yourself and forgo the factory warranty.

Tank heaters last 10 years and cost a third as much as a condensing tankless and sometimes more if the one has a tough conversion.

PS. I personally installed an 80% Noritz in a pool house 10 years ago and have never been back.
 

jetto-setto

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Hey guys, thanks for the info. The water in my area certainly isn't as hard as in some parts of the states at about 9 GPG, but that's still considered hard water. Rinnai does seem to make a scale-prevention device that is installed prior to the tankless heater. I think if I end up going the tankless/Rinnai route, I should really put that on for peace of mind. Good to know that with proper installation they can be reliable.

Thanks again for your help and I'll continue to give this more thought!
 

Dana

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Morgan- If you 've never been back, how do you know whether it's still working or not? :)

I lived with a Bosch for a dozen years or so, and it was fine- retired it still working when updating the heating system.

I've been using a Takagi as a combi-boiler heating both my house and hot water for more than a half-dozen years, and it's fine too. (I half expected it to crap out by now, but it shows no sign of giving up, despite being mostly neglected, save cleaning the crummy li'l screen filter every year or two and the occasional system water change when hacking on the radiation.) When it eventually dies I'll likely be dropping in a small mod-con boiler, though a small micro-cogenerator would be nice. (I had hoped there would be more micro cogenerators available in the US by then, and designed the system buffering accordingly, but it seems to not be in the cards.)
 

Dana

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If they don't call me, it's still working :).

You will need a Viessmann 222F I think.

I don't need a combi, just a boiler- the Viessmann would be overkill. The 48 gallon ErgoMax reverse indirect at the center of the mess buffering the system isn't going to give up for another couple or three decades at least (it has a lifetime warranty in residential applications.) Based on the modulation levels I'm seeing out of the Takagi when somebody is taking a long shower in the dead of winter, it would do just fine dropping in an HTP UFT-80 or a Burnham ALP-080, an 80K Munchkin or similar, with some flow tweaking (or a smarter pump) to keep the delta-Ts in a decent range under both space heating & hot water loads. Ripping out the whole thing to get the last 2% of efficiency out if it with outdoor reset wouldn't be worth it. With the current heating loads & radiation it keeps up at 125AWT, and the hot water performance is fine with the buffer set to 130F.

As currently configured at the end of a burn with the aquastat on the buffer set to 130F the EWT at the boiler is ~127F, but at the beginning of a burn or under sustained space heating load it's 118-120F, (lower, in "endless shower" mode), so I'd expect to get 92-94% average seasonal efficiency out of a mod-con once it's dialed in, but not 95%+. A mod con would take higher flow/lower delta-T than the Takagi, but simple-math design calculations indicate it wouldn't be a problem and it would even bump up the hot water performance a notch (due to higher turbulence on the heat exchanger coils, and a faster modulation ramp when running a fixed-temp output on the boiler.) It's possible I'd be able to knock the temp down a few degrees (but not 10), and pick up another percent or so in raw combustion efficiency.
 

Dana

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Sure, why not!? (And thanks for all of your shared insights to date!)

I think it's fair to say that I've gotten my $250-worth out of that surplus eBay Takagi! :)
 
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