Thoughts On Navien Vs AO Smith Small Tankless Propane Boiler

Discussion in 'Tankless Water Heater Forum' started by CORVAIRWILD, Mar 12, 2014.

  1. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    I'm building an office for my wife from our 3 car garage. 10'x20'. 4" concrete w embedded PEX over 2" styro over existing concrete. I am super-insulating the walls with double off-set studs so the fiberglass insulation overlaps, and adding a foot of fiberglass to the ceiling.

    The local plumbing supply carries A O Smith and Navien. A O Smith made in USA, my price $933. Navien is made in Japan $1160.

    Both exit thru the wall and will be mounted directly above my wife's desk. She works from home, so noise is important, and less is better. thoughts?

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  2. Reach4

    Reach4 Active Member

    Messages:
    1,897
    Location:
    IL
    AO Smith has a "15 year" but it is 12 years on the heat exchanger and and 5 years on warranty, but I don't know what the restrictions are. They give no warranty if you install it yourself.

    http://www.navienamerica.com/WarrantyInformation/ http://www.navienamerica.com/WarrantyInformation/NPE/ seems to exclude damage due to build up, but I don't see a specific hardness cuttoff. One exclusion reads
    They specifically say no warranty for any unit bought via the internet.

    For A O Smith the hardness limit number is 7 grains.
    So don't assume you get a warranty just because they advertize a warranty. Don't assume that I found all of the weasel words for you.
  3. zl700

    zl700 DIY Senior Member

    Messages:
    237
    Location:
    Texas
    First
    The AO Smith is a Takagi made in Japan and labeled AO Smith
    The Navien is made in S Korea

    Second
    Don't use a tankless water heater as a boiler for your radiant heat, you will be sorry in so many ways, too many to list here.

    Third
    It's an office why wouldn't you put the utilities in a mechanical closet to hide all the pipes, pump and wiring? All that would like like crap over a desk
    Last edited: Mar 12, 2014
  4. CORVAIRWILD

    CORVAIRWILD New Member

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    20
    Location:
    NY
    That's why I came here for advice. What should I use to heat the floor? I thot the tankless was THE way to heat in floor?!?!?

    There's only 9' exterior walls and I'd like to vent directly outside, in the back away from the street side. I could mount it on a side wall and runs along the shared garage wall, or I guess I could run the system on the street side...

    And the ceiling is 10', so if I mount the heater on the wall above the desk it's not to unsightly, and mount the expansion tank higher up, and use white pipes... I could build a small chase for the pipes

    Is there a thread here I should look at?

    And sorry to confuse the origins of the units, my bad
  5. houptee

    houptee Member

    Messages:
    181
    Location:
    Monmouth County, NJ
    What model AO smith are they quoting you that price?

    A Takagi TK Jr2 is worth a google search.

    If you plan to install it yourself they sell Navien, Rinnai, and Takagi so you could print it out and negotiate price with local supplier.
    Last edited by a moderator: Mar 14, 2014
  6. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
  7. houptee

    houptee Member

    Messages:
    181
    Location:
    Monmouth County, NJ
    Takagi and AO Smith formed a marketing partnership a few years ago.
    Like zl700 said the AO is a Takagi with different label on it.

    As far as price who knows guess he is quoting your full list price and does he actually stock it or does he order it and it comes via ups to his supply house?
    If so his inventory carrying cost is nothing, but he does have a brick and mortar storefront and the expenses to keep the place open.

    Its hard to try and support local businesses when the price is so far away from online prices but nobody pays me whatever i quote they shop around get 3 quotes and then still try to get you to throw in extra stuff or offer less its just business.
  8. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    Here's the quote. I dunno if they have it in stock, locally or at main store or drop ship.

    So what do you recommend I use?

    Attached Files:

    Last edited: Mar 13, 2014
  9. houptee

    houptee Member

    Messages:
    181
    Location:
    Monmouth County, NJ
    That AO model is equivalent to the Takagi T-H3J-DV/IN
    http://takagi.com/index.php?product_id=139&page_id=2

    His price is good its actually lower than what I find online for that model Takagi

    Question is do you only want to heat that 10x20 floor with it? Did you do any type of heat load calculation to size the required boiler/water heater?
    If so you might not really need to spend the extra money on a "condensing" water heater for that small of a load.
    The TK jr2 is not condensing that's why it is half the price of the quoted models but has 140k btu max capacity.
    It does require special cat 3 stainless venting you cannot use PVC to vent a TK jr.
    http://takagi.com/index.php?product_id=101&page_id=2
  10. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    No, I didn't do a load check, but a really well insulated 9x20 w 10 foot ceiling can't take much to heat. And this is just to heat this space, the rest of the house already has oil HW heat, but there's a concrete floored 10' breezeway in between.

    So no condensing? and how much is the SS stack compared to PVC? Does it require the same 12" clearance to a window? We're downsizing the window to accommodate that
    Last edited: Mar 13, 2014
  11. houptee

    houptee Member

    Messages:
    181
    Location:
    Monmouth County, NJ
    If you go out the top of unit with an adapter then elbow thru wall with a wall thimble then have a vent hood on outside you need total of 4 vent parts.
    The Z-Vent brand is less than the takagi branded venting parts and they add up to $158 in stainless from a site in Fla discounttankless.net or google designer plumbing

    The clearance from any type of building openings is less distance if the unit is "direct vent" meaning it has a second intake air pipe for combustion air vs. using air from the room.
    The direct vent conversion kit for takagi tkjr is $58 extra if you think you need it.

    So total would be around $786 from that website for Tkjr unit and venting, free ship, no sales tax.

    Your unit is 933 plus tax
    Last edited: Mar 13, 2014
  12. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    So why not the condensing? My application too small? And what outside/window clearance do I need? The shiny colorful brochure doesn't list any numbers.

    I'll go look at the link
  13. houptee

    houptee Member

    Messages:
    181
    Location:
    Monmouth County, NJ
    You have to download the full manual pdf from takagi link and read the section on venting, it shows diagrams of various window and soffit clearances etc but these are dictated by the local codes not the manufacturer of the equipment. In NJ we use the National Fuel Gas Code but NY might use something else.

    Im not saying the TKjr is better than the other units you were quoted, just making a suggestion for alternative unit since you have a fairly small slab, the bigger units you mentioned might be overkill on the btus since radiant is run at lower temps.

    If a condensing unit will save you a measurable amount of energy I do not know for sure, only that the cost difference is much higher, and you probably need a condensate drain pump etc so more parts and piping.
  14. houptee

    houptee Member

    Messages:
    181
    Location:
    Monmouth County, NJ
    Well first off there are "tankless water heaters" that can be used for space heating, like the models you have looked at, but they are not classified "boilers" so have no AFUE energy ratings, only the EF rating used to test domestic water heating.

    There are "wall hung boilers" that are made for space heating and have AFUE energy ratings like a regular boiler.

    Then in both categories there are condensing and non condensing models.

    So its hard to compare a water heater to a boiler based on the energy ratings because they are not the same tests.

    So keep googling around and see what other radiant floor systems installers have used and had good results with in your climate.
  15. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    Jeez... all true...

    But back OT... I was at another plumbing supplier, and the clerk suggested an electric boiler. Since I only have less than 200sq and 10' ceiling... I wonder if the solar cells I plan to power the house/office with will be able to handle the 25 amps the elec boiler requires? I have a meeting w the solar installer tmrw. I'll be sure to ask. Electric would require only a 10g cable-25 amps, no gas-bottle-chimney. Worth asking!
  16. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    I got a brochure for a Trinity LP boiler made by NYThermal... Made in New Brunswick Canada

    Looking over the brochures, some weigh 200lbs for a condensing boiler, another weighs 128lbs.

    I feel like I should mention that the subject has gotten off topic. Can we discuss my heating needs?

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  17. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    At the extremely low loads you're likely to be seeing here I'm not sure what the point of using a boiler OR at tankless would be (or even bother wih the radiant floor for that matter, but I'll leave that for another day.)

    Seriously, run a load calculation! (Even a dumb I=B=R approach would be fine.) I'll bet this place could be heated just fine with a cheap tank-type hot water heater.

    But at the price of propane you'd likely be able to heat the space at half the operational cost (or less) with a 3/4 ton cold-climate mini-split. (eg: Fujitsu AOU 9RLS2H, or Mitsubishi MSZ-FH09NA ), which would cost less than any of the ridiculously oversized boiler or tankless solutions you seem to be contemplating.

    The worlds-smallest electric boilers or a small tank-type electric water heater could heat the place using the floor PEX too, but would use about 3x the amount of electricity annually that a mini-split would. The mini-split can also air-condition/dehumidify the place during the dog days of summer too.

    If this place is off-grid there's no point to heating with ANYTHING that requires electricity, but if your PV array is going to be grid-tied the mini-split solution works. (And yes, they can probably cover your load even at -30F, just eyeballing the walls & windows in the pictures.)

    To get a really crude handle on the heat load, let's have a bit more info:

    How many square feet of window, and what is the window's U-factor or type?

    How many square feet of exterior wall, and how thick is the fiberglass in your double-offset walls?

    How many square feet of exterior door, and what type?

    What ZIP code is this (for best-guesstimate on outside design temps.)
    Last edited: Mar 18, 2014
  18. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    ZIP 12901

    We'll be ordering Marvin windows 50sq ft total, triple glazed

    All walls are "exterior". 2x20' in breezeway and garage, unheated tho

    2x9' window walls

    Fiberglass 3.5" original + 5.5" new and offset + 1' added to attic, 90d to rafters

    2x 36" exterior doors w magnetic seals, and I install them perfectly!

    We met w the SOLAR fellow today, really nice guy. He suggested we live there for 1 year to get a baseline of our consumption, and he suggested we meet with the Geo-Thermal installer for a quote.

    The PV install will run around $50k for 15KV(KW?). NY offers about $35k back, so our final out-of-pocket $15K or so, and we net meter here, so over the year we shouldn't have an electric bill if our current consumption is the same at the new house.

    I'll have to go see what a mini-split is... Never heard of it...

    Looked up mini-splits... not what we're looking for, no A/C required, we open the windows.

    https://www.google.com/search?q=Mit...a:en-US:official&client=firefox-a&channel=rcs

    I'm betting the Geo Thermal will run a Gazillion dollars... 1500sq ft house, 3.5" cedar logs, milled grooves to kinda seal things, and even with the wind and 0f temps, house is 58f and NOT drafty. We're not living there, but I've been working on the office and sitting in various rooms of the house for snack breaks. 4" styro in roof I'm guessing, maybe 6", w cathedral ceilings thru-ought.
    Last edited: Mar 18, 2014
  19. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    Plattsburgh 12901 has a 99% outside design temp of -4F. Assuming an interior temp of 71F that's a 75F delta-T/


    I'll assume solid wood, not insulated doors for a U-factor of about 0.5. With 2 doors it's a total of about 45 square feet. At design condition you're looking at door losses of about:

    U0.5 x 45' x 75F= 1678 BTU/hr (<If it's an insulated steel or fiberglass door you're looking at about 100 BTU/hr- so it matters.)

    You have 50' of triple-glazed that probably run about U0.20 for window losses of about:

    U0.2 x 50' x 75F= 750 BTU/hr.

    The 2x6 studs w/fg run about R13 after factoring in the thermal bridging, the offset 2x4' part runs about R9 after thermal bridging, the sheathing/siding/gypsum adds up to about R1, so your looking at a "whole-wall" R of about R23, for a U-factor of about U0.043 BTU/foot-degree hour for the walls. With a perimeter of ~60' and assuming 9' wall height you're looking at 540' of gross wall area, less the ~95' of window & doors leaves ~ 450' square feet of wall, for wall losses of about:

    U0.043 x 450' x 75F= 1451 BTU/hr

    I'll assume you have about R50 total in the attic after thermal bridging of rafters or trusses (it's probably better than that) for a U-factor of about 0.025. With 9x 20' it's 180 square feet, for ceiling losses of about:

    U0.025 x 180' x 75F= 338 BTU/hr.

    Add it all up and you get 4217 BTU/hr.

    Then subtract 350 BTU/hr for one seated-but-conscious adult human, 500 BTU/hr for a running computer, maybe another 250 BTU/hr for 75 watts of lights and you're at about 3100 BTU/hr that needs to be supplied by the heating system.

    Even if you DOUBLED that to account for air infiltration/ventilation and the losses through the insulated slab you are well-within the -4F output of the MSZ-FH09NA or AOU-9RLS2 either of which can deliver over 8000 BTU/R @ -15F. If anything they are arguably too BIG for the application to hit their optimum efficiency but even so they'll use only about 1/3 the amount of electricity of an electric boiler or hot water heater. Turnkey professionally installed cost would run about $3500 for either of those. Installing the outdoor unit in the breezeway or bracket mounted on the wall under rake of the roof where it's protected from roof-cornice fall and above the snow-drift depth is highly recommended- you don't want to be digging the thing up after every storm.

    A 4500 W electric hot water heater element on a cheap electric hot water heater delivers ~15,000 BTU/hr, so even that is more than 3x oversized for your 99% design load, and would be a cheap way to go if you insist on the radiant floor. With a design load is only ~3000BTU/hr and your average mid-winter load is 2000BTU/hr, with 180' of radiant floor it'll be warm enough to have some real cush-factor, but it'll cost 3x as much to run as a mini-split.

    You could also get there with less than $500 worth of 1000-1500 watt of radiant cove heaters mounted at the crown-molding level. If controlled with an occupancy-sensor type wall switch rated for 1500W of incandescents in series with a line-voltage thermostat the cove heater approach wouldn't use any power until/unless the place was occupied, and since they work by radiating heat at the humans and objects rather than convecting the heat to the air first it comes on quickly and is pretty comfortable while coming up to temperature, even if it's starting out at 55-60F. With the thermal mass of the slab fully inside the insulation and high-R building envelope if you get any solar gains at all it would probably stay above 50F. It's not tough to wire in a by-pass switch in parallel with the occupancy sensor if it turns out to be uncomfortably cold in the mornings in January, but during the shoulder seasons you'd be fine.

    The binned hourly mean temp in Plattsburgh is about +20F, a delta T of only 50F which means your average mid-winter load before subtracting off gains is about 2800 BTU/hr, but after solar gain and the ~1000 BTU/hr of humans, lights & office equipment your heat load during daylight hours on sunny days is effectively zero, but on cloudy days there will still be some. The heating/cooling balance point of this way-better-than-code building is likely to be at about 55F outdoor temps, and with the high-R envelope + the thermal mass of the slab the interior temperatures should stay pretty stable no matter how you heat the place.

    The last thing you want to do is put a propane-burner behind this miniscule heat load. The smallest boilers are 10x oversized for the load, and most mod-cons even at min-fire is going to be at least 4x oversized for the load. A cheap propane tank type water heater is also more than 8x oversized for the load.

    If you want to heat the FLOOR with a high efficiency air source heat pumps you could spring for the smallest Daikin Altherma which would probably come in at about $10-15K (half the cost of 1-ton of geothermal if you have to drill through granite), but it seems like overkill given that a $3500 mini-split would have you covered 2x over. The net efficiency of either the Altherma or the -FH09NA would be comparable to or better than a cheaper/crummier geo installation, if somewhat less a perfectly sized perfectly designed state-of-the art system.

    If you've never experienced heating with small mini-splits I should point out that they are fully modulating systems with a turn-down ratio of something like 4:1, and at minimum speed (where it would be running except for at 5AM on the coldest night of the year), the indoor head is literally quieter than your breathing and at max speed it's comparable to a refrigerator. The outdoor unit is similarly ghostly-quiet, since they all use variable speed scroll compressors (none of the at air-conditioning rattle) and variable speed DC blowers. With a "set and forget" approach to the mini-split temperature setting (recommended, since they have phenomenal part-load efficiency compared to full-speed), at your oversizing factor you would never even hear it unless you turned off the computer and held your breath, since it would only rarely have to step up to even half-speed.
  20. CORVAIRWILD

    CORVAIRWILD New Member

    Messages:
    20
    Location:
    NY
    Hmmm... Lots of intricate detail.. Nonetheless I installed 299' of PEX today in 3 loops. Plumber friend had recommended 200' in 2 loops, I figured if 2 is good 3 is better. I thot the idea of 3 shorter loops would be easier to regulate as the water wouldn't have as much of a temp difference from exit to return. I spaced the PEX about 9" apart.

    The goethermal will be for the 1500sq ft house. But we're waiting to hear from the installer. I expect it to be in the $30k range. The solar was $50, with substantial tax credits, none for the goe I think

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    Last edited: Mar 19, 2014
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