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How to interpret indirect water heater specs

For my new mod con install I'm looking at replacing the 25yr old HTP indirect. When looking at a replacement I'm limited on height of under 48". That limits me to most companies 30-40 gallon models. They all seam to use different criteria when determining the first hour rating like different delta T, different Btu input and gpm flow from the boiler, etc. Some of them list hx surface area and capacity. Should I pay more attention to the hx specs than the first hour rating? My top contenders are the B&W Power Stor SS 40 gal, and a HTP superstor 30 or Weil McLain Aqua Plus 35 gal.


Comments

  • Big Ed_4
    Big Ed_4 Member Posts: 2,783
    What is your hot water demand ?
    I have enough experience to know , that I dont know it all
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,516
    I would use the model with the largest tank. The more storage the more hot water you get. The storage capacity will give you more water than the slight differences in hhx capacity, btu input etc.

    Whichever tank you use it should probably be piped with 1" pipe
    Big Ed_4EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,826
    The pipe sizing for the boiler side is important.
    How close to the boiler is the DHW?
    A 3/4" pipe will move less BTU from the boiler to the water heater than a 1" pipe. Likewise a 1" pipe will move less BTU than an 1-1/4" pipe.

    This is a rule of thumb I used for pipe sizing.


    It is based on a 20° temperature drop from the supply to the return. I got this information from this very informative booklet called Zoning Made Easy If the boiler is within a few feet of the Indirect DHW, than you may get a little more heat energy than this chart. If the Indirect is under the steps and the boiler is on the other side of the basement, then you want to use a larger diameter pipe.

    You can have a 199,000 BTU Boiler connected to the Indirect with 3/4" pipe, and you will not get the full energy for the boiler to heat the water in the Indirect. That is because the smaller pipe can not move much more than 40,000 of the available 199,000 BTU's to heat the water in the indirect.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    MikeAmann
  • Karl Reynolds
    Karl Reynolds Member Posts: 62
    If you need extra capacity, HeatFlo makes a 44" tall 60 gallon tank, Buderus has a 79 gallon horizontal tank, and Viessmann has 53, 92, and 119 gallon horizontal tanks.
    Intplm.
  • THETRUCK454
    THETRUCK454 Member Posts: 20
    Big Ed_4 said:
    What is your hot water demand ?
    Just a wife who like to take long showers and melt her skin off every time.  

    I would use the model with the largest tank. The more storage the more hot water you get. The storage capacity will give you more water than the slight differences in hhx capacity, btu input etc. Whichever tank you use it should probably be piped with 1" pipe
    Definitely planning on 1" copper linesEdTheHeaterMan said:
    The pipe sizing for the boiler side is important. How close to the boiler is the DHW? A 3/4" pipe will move less BTU from the boiler to the water heater than a 1" pipe. Likewise a 1" pipe will move less BTU than an 1-1/4" pipe. This is a rule of thumb I used for pipe sizing. It is based on a 20° temperature drop from the supply to the return. I got this information from this very informative booklet called Zoning Made Easy If the boiler is within a few feet of the Indirect DHW, than you may get a little more heat energy than this chart. If the Indirect is under the steps and the boiler is on the other side of the basement, then you want to use a larger diameter pipe. You can have a 199,000 BTU Boiler connected to the Indirect with 3/4" pipe, and you will not get the full energy for the boiler to heat the water in the Indirect. That is because the smaller pipe can not move much more than 40,000 of the available 199,000 BTU's to heat the water in the indirect.
    The indirect will be about 6' away from the boiler.  

    If you need extra capacity, HeatFlo makes a 44" tall 60 gallon tank, Buderus has a 79 gallon horizontal tank, and Viessmann has 53, 92, and 119 gallon horizontal tanks.
    Didn't even look at those companies, I'll take a look
  • NotFromHere
    NotFromHere Member Posts: 1
    I’m no plumber or expert of any kind, but I can speak from the experience of having replaced a conventional 40 gallon gas water heater with a Weil-McLain Aqua Plus 35 gallon indirect hot water heater connected to our Weil-McLain Ultra 105 boiler.

    We’ve had the Aqua Plus for just over two years, and it’s honestly like having unlimited hot water. We’re a family of four (two teenagers), and we have never run out of hot water since we had it installed.

    Its recovery time is super fast, and you can tweak it by going to the max of 190 on the boiler and then set the water heater higher as well (higher than the 120 degree water that the mixing valve provides). Our installer set it to 190 on the boiler and 140 on the water heater. I’ve since changed it to 180 and 130 and that’s been fine. 

    Not sure they make the 35 gallon version any more, but I’d probably be just as happy with the 30. 
  • clammy
    clammy Member Posts: 3,111
    There's a few others out there like bock and turbo max tanks .I ve used both and haven't had any issues aside from yearly or bi year anode rod replacement . the htp tanks are nice except no well just a tank surface mounted sensor . Any tanks output can be increased by increase tank temp and installing a mixing valve which is code . The down fall of higher tank temps is the increased rate in which lime and calc will build up including a simple aquapur scale inhibitor lower the build up and yearly or bi flushing of tanks also help reduce build up and increase longevity of the tanks . Also no indirect tank install is complete and warrantied unless the homes water pressure is checked and a portable domestic expansion tank is installed . When installing a turbo max style tank be sure to include the extra water volume to the heating size when picking your heating systems expansion tank . Final note but being your using a mod con its a given indirect deserve there own circulator pump equipped w check valves and when using a turbo max style tank be sure to include a flow check on the return also especially if your heating w low temps being thermal migration does occur and ends up short cycling the tank as the heat migrates to the heating side when heating is operating a outdoor reset at low temps . Been there and seen it .
    peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • THETRUCK454
    THETRUCK454 Member Posts: 20
    Looks like the Lochinvar Noble boiler can take either a aquastat or a tank sensor. 






    The Wel McLain Auua Plus indirect looks to use a tank sensor hooked up to a digital aquastat.  Would it make sense I could just wire the tank sensor right into the Lochinvar Noble and skip the Weil McLain controller ?  With all 24v thermostat/aquastat does the signal correlate tho temperature the same? 



  • hot_rod
    hot_rod Member Posts: 22,120
    I prefer to run the indirect from the boiler control. That way you have all the data and readouts in one controller
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterManmattmia2
  • THETRUCK454
    THETRUCK454 Member Posts: 20
    hot_rod said:
    I prefer to run the indirect from the boiler control. That way you have all the data and readouts in one controller
    Yea that was my plan, just wasn't sure if I needed anything else or I could tie the Weil McLain Aqua Plus right into the boiler by not using the included digital readout
  • hot_rod
    hot_rod Member Posts: 22,120
    You need the Weil tank sensor, which I think is a Honeywell that you can get at Johnstone Supply for less $$
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • THETRUCK454
    THETRUCK454 Member Posts: 20
    To being this back up I'm changing gears on which brand indirect and going with the Bradford & White SS Powerstor. It comes with an immersion Honeywell aquastat.  I am unclear on what is required to switch that out for a tank sensor.  
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,002
    edited April 3
    If you have a Lochinvar boiler, didn’t you say that it can take either a sensor or aquastat?

    If you want to go with a sensor, get one from Lochinvar. 
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
    EdTheHeaterManmattmia2
  • hot_rod
    hot_rod Member Posts: 22,120
    If you want to use the aquastat that comes with the tank, wire as shown in the manual pin 7&8

    If you want to use a sensor, which you need to purchase, wire as shown

    If you use the sensor, pull the aquastat out of the tank and insert the optional sensor. If you use the sensor, the boiler control runs the tank

    which option do you want to use


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • Zman
    Zman Member Posts: 7,569
    The sensor will have an Ohm rating. Generally, if the rating is the same between 2 manufactures they will work interchangeably. If you go with the one supplied by the boiler manufacture you don’t need to think about it, it will just work.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,826
    edited April 3
    This is not Rocket Surgery. The temperature sensor can be the aquastat supplied by the tank manufacturer, or the thermistor supplied by the boiler manufacturer. The location is the same for either sensor. That location is where the tank manufacturer places the aquastat.

    Hope this helps
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • THETRUCK454
    THETRUCK454 Member Posts: 20
    I understood the wiring aspect, it was just unclear on the physical aspect.  I just doubted it was as simple as unthread/remove aquastat and install the tank sensor.  Sounds like it is that simple.