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heating with indirect

radmix Member Posts: 194
I just went to a  project today and the previous heating contractor's used a super stor indirect to lower the boiler temp for a radiant application. 5 zones of heat all radiant and I will be adding a 6th zone. Im trying to sell the homeowner on a variable speed injection mix, Can anyone tell me the efficiency of heating with an indirect vs. heating with a mix directly off of the boiler loop.


  • Ironman
    Ironman Member Posts: 6,900
    Tank Temp?

    Is the indirect's temp being controlled by some form of reset or just a simple aquastat?

    If reset is being used, then I would tend to think that using the tank would be more efficient as it would eliminate boiler short cycling.

    If multiple temps are required, then the tank would still be beneficial but the various temps would have to be created past the tank.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • radmix
    radmix Member Posts: 194

    I would think that heating the space directly on the boiler loop would be more efficient than going through a second heat exchange. There's always going to be a loss through the exchange. I'm also questioning heating 6 zones of radiant in a 4000sq house using a ss45 gallon water heater is enough. I will be using outdoor reset with the variable speed injection system.

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    More questions....

    What is the heat transfer capacity of the tank/heat exchanger when there is only a 60 degree differential in working fluids (180 vs 120)?

    Why would one put a heat exchanger in a closed loop system (non oxygen barrier tube)?

    The tank will add bufferage to the system, but I am with you, if at all possible, eliminating as many heat exchangers as possible will lower the operating boiler temperature needs, which equates to energy $aving$.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • radmix
    radmix Member Posts: 194

    I'm also questioning the life of the water heater since its made for DHW production not space heating. I'm sure the warranty would not be honored if its used for space heating. The house is only 3 years old.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,216
    it is easier to do heating than

    to do domestic heating from a dissolved gas and mineral standing. Also a lower delta T so less thermal stress on the tank and heat exchanger. It is not a bad idea what was done IF done correctly.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    this is an odd choice

    if that's a high temp boiler, this doesn't provide boiler protection unless we're counting on limited heat transfer through the coil. is it a particularly bad indirect?

    in other words if the tank is 100 degrees and the boiler is trying to heat it up, how fast do you really get over the boiler minimum temperature?

    Maybe it's not too bad, and that is an argument for the heat exchanger, since if this was just a storage tank you would NEVER get over boiler minimum and would rot out the boiler if you constantly fired it at low temp, just as if the radiant was connected directly without mixing and the water temp set low.

    but I suspect it's probably condensing more than anyone wants if it's connected to low temp radiant and/or if it's using reset without a boiler minimum/protection control feature.

    tank's already there though, could use it. make it high-ish temp (boiler protection) and inject out of it.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • radmix
    radmix Member Posts: 194

    I returned to the project today to find that the radiant side of the indirect was completely corroded with rust and slug. The radiant tube used is Onyx 200, loops were off of an extended header. This tube should be oxygen barrier so oxygen must be leaking in from somewhere, Maybe this is why they used an indirect like Mark stated. All of the circs are cast and piping is black. When I started to unthread the expansion tank my finger when through it, then upon further investigation it was found that the piping of 11/4" pipe had a circumference of about 3/4". I'm going to re pipe the system with a plate heat exchange and stainless circs.

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    You are not alone...

    I've heard from NUMEROUS people about corrosion issues with that product. And, in ones minds eye, you WOULDN"T expect to see that much corrosion...

    My theory is that at each barbed connection, when the tube is cut, the inner tube gives a direct path for parallel O2 ingression. No proof either way, but WAY too many people seeing the same field conditions you are.

    The next thing that happens is embrittlement of the hose. It sounds like Rice Crispies in milk when you move it...

    Good catch, and good luck.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
This discussion has been closed.