Tankless in an unconditioned NJ attic

Discussion in 'Tankless Water Heater Forum' started by North Jersey, Jan 21, 2009.

  1. gregsauls

    gregsauls Homeowner

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    FWIW, my tankless is about 40 feet from our master bath. In comparision between our old tank setup and our tankless, it takes about 8 seconds longer to get hot water now to get to the shower.... No biggy. You won't have a problem filling that 200 gal tub that's for sure!

    On another note, it would scare the crap out of me to have pipes to tankless in the attic that could freeze. Talk about a making a mess of the house. But maybe they do that up north and don't think twice.
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    While the anti-freeze stuff IN the tankless might prevent it from bursting internally, it won't do much of anything to the pipes coming and going from it. And, as noted, if you have a power outage, all bets are off. Keep in mind that all of that combustion air is being pulled through cracks in your house, bringing in outside air (and if it can't get enough, creating CO). This negative pressure will also affect things like a gas stove, dryer, fireplace, etc. This will mean more air you have to heat, killing any savings on the tankless. In the winter, what does it say about gpm flow rates? The things often adjust the flow based on the incoming water temperature. So, to get it warm enough, you might only get 3 gpm, so to fill your 200 gallon tub, would take maybe over an hour. In that time, what is in there is cooling off, so you'd be tempted to start with it much hotter, wasting more energy.

    So, really, what kind of flow rate and outlet temperature can you get with say 40-degree inlet temperature water? Are you willing to wait an hour to fill the tub in the winter? It should go much faster in the summer, but maybe not depending on the depth of the well and the size of the bladder storage tank. The solution, if you stay with tankless is to maybe use two units in series, or get a much bigger unit, which would have even more combustion air makeup problems (unless you go with direct vent). Is your gas line big enough, too? A good 3/4" valve to your tub could draw 14 gallons/minute and fill the tub quickly IF there's enough flow. You sure your pump can keep up and the well produce enough? That's a pretty big tub!
     
  3. Ladiesman271

    Ladiesman271 Homeowner

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    Takagi specifies type 3 venting. The Takagi units have fan assisted exhaust. You can't vent those units into a chimney per the gas code book. That so called "high temperature" claim means nothing to me.

    I have an older atmospheric vented ELM Aquastar that only requires a single wall gas vent into a gas vent or chimney. B vent is preferred over single wall in a cold climate (gas code). My unit is 5" B vented to the 8 x 12 (?) clay tile liner of the masonry chimney. This conforms to the 7 X rule.
     
  4. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

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    the clay liner was the problem

    that is about what I had palnned, and for me it would
    have been almost a direct dump into the 8x12 tile liner...

    I was told that Takagi frowns on that....becasue it blasts out of the unit almost like a jet engine...


    So if they tell me it might burn my house down,

    I generally take notice..
    I will have to do some more ivestigation....




    This sort of makes me wonder how many people
    have thrown away the instruction manuels and just
    rigged up these things to what loooks like will work..???.
     
  5. Ladiesman271

    Ladiesman271 Homeowner

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    I think the issue is moisture, not excess heat. You ever hear the story about the exploding tank type water heater? How about the exploding house?

    I have read the 1996 Gas Code Handbook, and what it pretty much says in Section 11 is that fan assisted units can not vent into a masonry chimney. You need to have all old type draft hood units with no fan assist on any unit connected to the vent. There are various tables in that vent section.

    Anyway, the handbook also states:

    Exception: The installation of vents serving listed appliances shall be permitted in accordance with the manufacturer's instructions and the terms of the listing.

    The way I understand the gas code, since the Takagi units (all fan assisted) require the type 3 vent that is what has to be used. That means follow the Takagi instruction manual.

    If my present tankless ever goes bad and is not repairable, there is no current B vent unit around that has a thermostatic water temperature control. I will be forced to do a chimney reline or something else if I need to replace my present unit.

    I still have my 50 year old original hot air furnace that I am looking to replace in the near term. The plumbing inspector said that as long as the water heater drafts properly after the old FHA heater is removed from the shared vent, I only have to conform to the 7 times rule for the water heater.
     
    Last edited: Jan 22, 2009
  6. Dana

    Dana In the trades

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    Yep, the issue with the newer higher efficiency forced-draft units is condensation. With less dilution air they get better controlled higher combustion-efficiency, but less dilution air also means higher CO2 concentration, which lowers the exhaust's dew point. That, combined with the lower exhaust temp due to the higher-efficiency heat exchanger, stack condensation is all but guaranteed (even in side vented units.)

    The older atmospheric drafted units like the E.L.M. never got much above 80% combustion efficiency, whereas the newer ones are all in the mid- or even high 80s. The new ones are in many respects more akin to low-mass modulating boilers than the old-school tankless heaters.
     
  7. tourne

    tourne New Member

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    I don't think these things are meant to be installed outdoors in a freezing climate. Takagi says that their freeze protection is only good to 5 degrees F. Your going to be running a lot of electricity to keep that thing from freezing all winter long.
     
  8. North Jersey

    North Jersey Member

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    You're right, I think most of the outdoor models still need protection from freezing temperatures. The only basic difference between my indoor model and the outdoor model is the vent. I talked to Rheem and several techs told me that an attic install would be OK as long as my vent is sufficiently long. The inline condensate drain seems like a bad idea, especially if the heater will be in close proximity to the termination. I'm going to do a short offset with an elbow condensate drain to avoid freezing.I'm going to place the pex under tented insulation in the attic. I've also considered putting a small electric heater in a vented enclosure in the attic.
     
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    It's my understanding that you don't see a lot of condensation until the efficiency gets a little higher. My boiler (obviously not the same as a tankless), condenses even in the summer when it's 90-degrees out (it's at about 95%). My old boiler was 88%, and there'd sometimes be drips out the exhaust vent (the horizontal section had to have a downward pitch to ensure it didn't fall back into the burner). It was hot enough to ensure it couldn't condense for at least a few feet, and you had to turn from vertical to horizontal before that.
     
  10. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

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    they are menat for florida and arizona

     
  11. North Jersey

    North Jersey Member

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    *UPDATE*

    Well, the freeze kit thing is not available for any new models.

    At any rate, I just called Rheem again and they assured me that the water heater would survive -30 amibient temperatures. They said the only real concern is having a vent that is sufficiently long. They recommended a cold-weather vent kit with a damper-style end cap.
     
  12. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

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    good luck.....


    I dont think I would trust anything that Rheem says.
    never trust a Techey that teaches theory.....


    yes, -30 that is pretty damn cold, but it dont take that to freeze pipes
    ....

    you had better be installing that unit with some sort of drain pan under it. Something Like a washing maching pan with a drain to the outside...

    ....just in case those Rheem techs are wrong....


    Also, I dont understand how the water lines going to and from this unit in that -30 temp area attic in New Jersey are supposed to keep from freezing and flooding your home either...


    are they telling you to run heat tape on all the lines
    all the way to the unit???


    and if the unit sits without comming on for a whole day
    in those harsh conditions, wont that coil get a little frosty??


    is their some sort of fail-safe on this ??

    Being installed the attic of your home,

    I would be very hesitant about this....


    .
     
    Last edited: Apr 28, 2009
  13. North Jersey

    North Jersey Member

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    Yeah, the attic won't be hitting -30 here. -15 would be a record setting day. We don't go negative very often. The average low during the coldest part of the year is 14.

    At any rate, I'll be running the 1" pex underneath the insulation. The only exposed area will be the 18" portion up to the water heater. Maybe I'll just run the heat tape for the last few feet. I probably will put a drain pan under the unit. The problem with putting the unit in my basement is supplying air for combustion. 199k btus requires a little more volume than we have down there.
     
  14. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

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    small hint....

     
  15. North Jersey

    North Jersey Member

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    What do you think about extending the house envelope to the attic, i.e., removing insulation between the ceiling and building an enclosure around the heater? I would have to put in a fairly large louvered vent in the door. I guess I could always put in a couple of thermostatic outlets for heat tape and a space heater.
     
    Last edited by a moderator: Apr 29, 2009
  16. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    There are all sorts of fire code and structural issues with moving something like this into the attic and opening up the space. At least a tankless won't weigh as much as a tank would up there - most ceiling joists aren't designed for that kind of point load of a tank.

    Some of these things can be installed in small spaces like a closet...is there one near the master bath that could be usurpted for that use? You'd still have the makeup air problem, but that may be doable.
     
  17. Dana

    Dana In the trades

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    A 200kbtu/h burner needs much more than a dryer hose for combustion air unless it a sealed-combustion setup. Backdrafting or lean operation due to wind-driven and exhaust fan pressure differentials are real possibilities (even in forced-draft models.) Good luck passing inspection if you're just plopping in a dryer hose into the space. (Good luck with getting it INSURED too.) 200kbtu/h is more burner than many/most home heating boilers or furnaces in NJ, and needs to be treated accordingly.

    Usually the freeze protection on these suckers relies on having reliable power. If an ice storm took down all the lines an you're out of power for a few days in winter (as happened to me this past December), if the unit is outside the thermal envelope of the building you're basically screwed. (Which DIDN'T happen to me. My HW heater lives in an insulated conditioned basement, it never got below 40F even on nights when it was 10F outside.)

    There are many good reasons (well beyond the scope of a hot water heater discussion) for converting attics into sealed, insulated-rafter conditioned or semi-conditioned space and dispensing with attic venting. It's both easier and better than you might think. A condensed encyclopedic overview of published research lives here:

    http://www.fsec.ucf.edu/en/publications/pdf/FSEC-CR-1496-05.pdf

    There are also very good reasons for going with sealed-combustion water heaters & boilers, especially if you have tightened up the place a lot (or plan to.) Takagi makes sealed-combustion kits for all of their hot water heaters, and other manufacturers have models/kits that are sealed combustion as well. Backdraft preventers on the venting offers quite a bit of freeze protection from wind (assuming it's inside the thermal envelope of the building) but can only be used on forced-draft models, (which would be most models over 100kbtu/h- I'm less familiar with Rheem, but I'd be surprised if it wasn't.)
     
  18. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

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    That sounds like a lot of WORK to me


    the last time I re-did an attic, I sort of remember it being a lot of nasty , dirty , hot and
    god awful grimey work......

    and you are wanting to do all this just to get your tankless unit up there...


    basically you are going to increase the overall area of your home that needs to be heated , increaseing your yearly heating bill and cooling bill,
    I suppose that is a good thing if you ahve been wanting to do this anyway someday...


    but to go through all this work just to be able to
    save a few dollars a month with your tankless water heater...???


    Why not put it in the basement, and simply put in a large enough
    vent to the outside of the home for air>???



    anyway, enough on this topic,

    you do whatever makes you happy,
     
    Last edited: Apr 30, 2009
  19. ChuckS

    ChuckS New Member

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  20. North Jersey

    North Jersey Member

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    *update*

    The plumbing inspector said he'll probably want me to open up the attic to the conditioned portion of the house. I don't think he realized that my home will likely not provide sufficient combustion air for a 199k btu water heater. I could place the water in a basement utility room next to the water softener and the expansion tank, but boring a 5-1/2" hole for combustion would cause the same sort of freeze problem as putting the unit the attic, right?

    Is a buying a direct-vent unit my only practical option at this point?
     
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