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radiant boiler

keyotekeyote Member Posts: 546
my designer [ im installing} really seems to hate boilers for radiant  he says the low flow  1gpm burns them out and they are too expensive when tankless water heater are better, this is the opposite of everything ive read, but hes got a lot of experience and though ive done a fair amount of hvac and plumbing even a bit of radiant im no expert . i thought he was maybe operating on old information since hes kind of old but hes full of numbers specs etc i know enough to know hes not bullshitting but not enough to know if maybe hes just got a maverick perspective worth considering. i asked if it was the condensation from the low temp that burnd them out thinkng he didnt get the whole stainless modcon thing but he says no its the thin wall tubes get hot spots on low flow high btu i thought the tubes were now usually in a block to heat exchange for a dhw loop. any thoughts, if you guys are adament recomend a boiler i was lnterested in triangle tubes newer  also dans recomended one on the home page here , this guy swears by tagagi t2s

thanks again

 im doing 5000 sf 5 story brick in brooklyn


  • keyotekeyote Member Posts: 546

    hes also worried about short cycling  particularly with out door resets, yeah i know but his point is a solid breick house with spray foam insulation takes days to change temperature , this is true in my house , so by the time the house changes the weather outsides changes again and since im not a thick slab radiant heat sink but rather a warmboard under hardwood situation it doesnt take long to warm the room. kind of made sense while crumbling what i thought was extensive research. below is a design he did looks pretty good to me any thoughts- thanks
  • Aaron_in_MaineAaron_in_Maine Member Posts: 313

    The boiler he is talking about probably has a Giannoni type heat exchanger. If you are doing a radiant system with low temps I would use a fire tube boiler triangle tube is one of many. Giannoni style boilers are good too when installed right.
    Aaron Hamilton Heating
    [email protected]
  • kcoppkcopp Member Posts: 2,774
    Didnt we...

    just go over this? Hot spots? If you ahve the heatloss done(and at this point I might get a 2nd opinion on that) there won't be short cycling.

    Tankless water heaters are for domestic hot at 45* out at 120-130*  not in at 130* out at 150*.... again wrong tool for the job.

    Then there is the recirc thing. Some tankless water heaters if you run a recirc loop to them it cuts their warranty in half.... thats all you are doing in a heating system is recirculating.

    Its up to you... good luck.
  • GordyGordy Member Posts: 7,122
    edited March 2013
    Hx designs and delta t

    The reason or part of why tankless are not as efficient in a radiant application is hx design from a tankless to a boiler. The larger the delta t the faster the btus transfer. With that being said the hx in a tankless is smaller than one in a comparatively sized boiler. That's how the btu ratings are higher in a tankless. And why the are smaller. When used for radiant the btu transfer is different because the delta t is narrower. That's why boilers have larger hxs
  • GordyGordy Member Posts: 7,122
    edited March 2013
  • Paul PolletsPaul Pollets Member Posts: 3,022
    Designer, et al

    If your designer doesn't know the particulars of current mod-con design, you're at a disadvantage. I can't read the schematic details, but I presume the solar array also assists the heating demand, as well as DHW. Drainback systems have their place, but solar glycol is far easier to maintain and doesn't require a large pump to push the fluid. Installing what I can see on the schematic will require significant skillset.

    I'd be using Viessmann components to simplify and you may want to spend some time looking at their schematics under current product documentation:
  • RobGRobG Member Posts: 1,850
    Second design opinion

    You are obviously doing a high end heating system. I agree with all of the above responses. You should contact NRT Rob (Northeast Radiant Technologies). He posts on this site regularly and is a very experienced designer. If you are going to the time and expense of installing this high end system, you better get it right the first time. Anyone who recommended a tankless water heater for a radiant system for my home would be walked straight out the door.

    Just my opinion.


    P.S. here is NRT's link 
  • GordyGordy Member Posts: 7,122
    edited March 2013

    With RobG

    If your doing solar to save money why blow it with a tankless that will be less efficient. Kind of like spending all that money to buy a hybrid car with a 350 engine for the highway economically speaking.

    Is the designer throwing the tankless in the design to make the whole design more affordable so it has a better chance of comming off the drawing board to life?

    A good designer embraces old, and new technology melding the two into an efficient comfort system. This holds true in all types of construction design.

    There are all types of designer mentalities. The hardest part is getting inside their head from a blueprint perspective. Sometimes there are out right mistakes, and some are just unthought of issues that may never be apparent until construction phase.
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