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Thread: Problem with Takagi & Radiant Heat &Domestic Hot Water

  1. #16
    Master Plumber master plumber mark's Avatar
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    Talking your moral reaponsibility

    Quote Originally Posted by jdgoodman View Post
    99* Of Takagi calls i go on i find a reason they are not functioning. Its always the same story, Bad venting, gas issues, poor placement or just no maintenance. I thought i was a tankless pro until i went to Takagi's plant in California for their training class. Needless to say i discovered i was far from it. People blame the units but in most cases it is the installer or the owner.
    how do you handle a situation where the home might burn down becasue of the way the home owner installed their tankless waterheater???

    do you just write a warning on the bill you hand them to cover any future liability????

  2. #17
    In the trades Dana's Avatar
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    Quote Originally Posted by master plumber mark View Post

    Piggey #2 This fellow decided to install his Bosch into his regular furnace flu pipe
    going up the center of his home... ........oh my goodness, thats a no..no........

    I told him that he might burn his home down that
    way, because his metal chimmney was not designed or rated for the intence heat
    that the tankless would put out,
    I dont think he wanted to hear what I had to say
    I was being too blunt explaining to him that
    that his house might burn down.....
    S'plain me better about this intense heat the tankless is puttin' out?

    I thought the problem for most tankless vent was the coolness of the exhaust creating a potential for flue condensation & corrosion, but those bottom-of-the line atmospheric-drafted Bosch units are low enough efficiency that with the designed-in dilution air makes 'em ventable with the cheap B-vent (provided the draft is sufficient for both appliances whether one or both were firing.)

    Some may require double-wall B-vent, but only the higher end forced draft versions require Z-vent. But again, it's the LACK of intense heat and the relatively high dew point of the undiluted exhaust of the forced draft versions that's the problem, not the high heat intensity that's the problem.

    Vented into improper stack types I'd be more concerned about carbon monoxide hazard from corrosion pinholes than fire.

    What model was Piggy #2's?

  3. #18
    Retired Defense Industry Engineer jadnashua's Avatar
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    Some of the tankless systems use 200K BTU or more, which is a pretty fair amount of heat. Even at their best efficiency, the flue temp can be pretty high. And, the volume of air is substantial, too. Don't put one in without either closed combustion or adequate makeup air and, follow the flue requirements of the manufacturer carefully.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #19
    In the trades Dana's Avatar
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    Quote Originally Posted by jadnashua View Post
    Some of the tankless systems use 200K BTU or more, which is a pretty fair amount of heat. Even at their best efficiency, the flue temp can be pretty high. And, the volume of air is substantial, too. Don't put one in without either closed combustion or adequate makeup air and, follow the flue requirements of the manufacturer carefully.
    I'm not sayin' that there couldn't be any number of problems with the installation, only that most fuggups would lead to a CO poisoning hazard before a fire hazard.

    Most of the cheapo atmospheric vented BOSCH units are under 150kbtu in, and don't have flue temps any hotter than the output of similar-sized furnace burners, and run about 80-82% combustion efficiency. But I could easily believe the height/diameter of the stack wasn't up to snuff for both appliances. But there are plenty of B-vented multi-appliance stacks in the world that aren't hazards, even if the appliance vendor (rightly) warns against doing it that way. (IIRC in MA it's allowed, but the draft has to be empirically proven. Cood be rong, offen am...)

    A typical 25% excess air atmospheric vented burner running in the 80% range will have a net-stack temp of ~400F (which would be ~465F if the combustion air is drawn from a typical basement) before dilution air, but the dilution air brings down to ~300F entering the vent, with the dew point of the exhaust lowered to 100F or less. This is where I'd expect the cheap Bosch units to live. If it's efficiency is in the low 70s the net stack temp might be 600F, but I don't think any tankless units sold run combustion efficiencies much lower than 77-78%, which would be ~500F net, at which point it could withstand huge dilution cooling with no chance of stack condensation, even in a masonry chimney, yet scant fire hazard unless the vent was installed with non code-compliant clearances to combustibles.

  5. #20
    Master Plumber master plumber mark's Avatar
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    Talking just read the damn manual

    most average homes have maybe double wall venting .....not SS pipe ...

    I dont know what size Bosch heater they had,
    but I am sure that it was recommended in the manuel to vent it separately out the side of hte home...

    if the home burns down, the the insurance company can possibly worm out of paying the fire damages beause of something improperly installed..

    I would be willing to bet that you could put a peice of something falmmable next to that
    chimmney near the Bosch heater and it easily could ignite.......

    and I dont have a clue what he
    has in the attic,, I have seen boxes and christmas trees leaning right on the metal chimmneys many times before...

    now wether it is cool enough by the time it gets up there is his problem and gamble...



    .



  6. #21
    In the trades Dana's Avatar
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    Some of the Bosch low-end units (up to and including the 1600 series) have side-vent forced-draft kits available, but most are installed with natural draft & B-vent, and run around 80-82% combustion efficiencies with modest but not super-low stack temps.

    In the Bosch lineup only the near-condensing forced draft 2400 & 2700 series require stainless venting, due to the low temp undiluted exhaust gas which results in large amounts of slightly acidic flue-condensation. Those series operate at around ~86% combustion efficiencies, ~200F net, for absolute exhaust temps under 300F (figure 250-ish) in normal conditions.

    Next time you install a forced-draft tankless that requires stainless vent, measure the exhaust gas & stack wall temps- you may be surprised. Hot to the touch, yes but well below the kindling temp of most construction & household materials- cooler than the glass surface of a 100W incandescent bulb installed in a floor lamp with a paper lampshade. (How much did you want to put on that bet? ;-) ) A Christmas tree won't light-off even held directly in the exhaust stream (try it!). It may outgas highly flammable volatiles with smoky appearance, but it'll still need an ignition source other than the stack itself. It's the intensity of the condensation, not the intensity of the heat that demands the stainless.

    If it's one o' those, Piggy-B probably won't need to worry about collecting on his fire insurance- he'll be long dead from the carbon monoxide poisoning by the time it catches on fire. The weasel clauses in the LIFE insurance may need attention though... ;-)

    If he installed a power-vented unit in a shared stack configuration with an atmospheric-drafted furnace (or conversely) he's clearly suicidal/homicidal. But if they're both atmospheric drafted it may go forever (or until the miserable thing craps out) without significant hazard unless they actually lean a Christmas tree up against the stack after a decade of neglect raised the stack temp to over 450F (from diminished combustion efficiency), or the main vent was severely undersized for the combined full rated output of HW + furnace exhaust flows at the outset. Backdrafting & CO poising would still be the more likely immediate hazard than fire though.

    There are all kinds o' DIY idiots out there though, which is why some states (including MA) specifically disallow DIY installation of ANY gas fired combustion appliances, no matter how simple.

  7. #22
    In the trades Dana's Avatar
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    Took me a bit of search to find it again, but....

    Next time you run into suicidal Piggies looking to end it all via kludgy venting schemes, save your breath (and possibly their lives)- get their email address and send 'em this link to an archived copy of the (only slightly dated) GAMA "Venting Done Right" flash video primer on the subject:

    http://www.slantcom.com/images/gas-a...ce-venting.swf

    It's short, takes way less time than trying to explain it over the phone without cheezy graphics to help explain it. If they don't call back, it's on them.

    (A lot of people need help with understanding the orphaned hot water heater flue condensation problem too.)

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