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I've been asked to re-pipe a mikvah.  A mikvah is a heated pool used in Jewish cleansing ceremonies.

The existing mikvah uses a pool heater in a separate room next to the mikvah.  It was explained to me by the rabbi that this mikvah was not installed properly; that the water in the mikvah must stay in the mikva and not leave the room to go through the heater, pump and filter.

They have ordered a heat exchanger (shell & tube?) that will sit in the mikvah and want a wall-mounted boiler to serve it.  The existing Raypak pool heater will not heat to 180F.  Can any of you make a boiler suggestion?  An "on-demand" heater might work, but I want something beefier (non-condensing) that's meant to operate at higher temperatures.  The existing pool heater has an input rating of 181,000 BTU's.

Also, I'd like to pipe it in copper, but don't know if copper is resistant to chlorine.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab


  • Paul Pollets
    Paul Pollets Member Posts: 3,617
    Mikvah expert

    ...would be Moses Fishman. ([email protected]) He designed and installed one of the largest mikvahs in NYC. He's a friend of Dan's (and mine) and should be happy to answer any questions. Tell him I sent you.

    Hot Rod wrote an article about him and the mechanicals:

  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,283
    Yes, Moses

    I visited that one. It's the largest in the world - a marvelous blend of high-tech and old-time religion. He can help, Alan. Nobody does it better.
    Retired and loving it.
  • hot_rod
    hot_rod Member Posts: 19,271
    custom HX

    that Moses and Kal designed and built for that job, it fits under that stairs. I believe they had it plated before it went into the bath.

    Lots of flow and HP = pipe size, to bring the tubs up to temperature quickly.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • NYplumber
    NYplumber Member Posts: 503

    Moses is the one to speak to! He does a supper fine job with mikva heat design.

    Let us know how your job plays out.
  • Moses
    Moses Member Posts: 93
    Mikvah Heating

    Hi Allen; Please call me when you have a chance @ my cell 347-203-0515


    Moses Fischman
  • Moses

    Thanks everyone for turning me on to Moses; what a guy!  He emailed me and then called me to offer his magnificent morsels on mikvahs.  With a name like Moses, I trust him.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hourTwo btu/ per sq ft for degree difference for a slab
  • Kal Row
    Kal Row Member Posts: 1,520
    2f rise every 70sec,,,

    that's with the reg pump, with the emergency/backup pump ([email protected]) it does 3.5f rise in same time - scary - the only mikva on the planet with a secondary aquastat acting as a hi-limit control - cause this coil can cook the little pool in short order!!, i also have a design for a stainless one built with 1" tube only 4 rows deep - the layers are actually staggered up and down to maximize the infra-red visibility of the coil to the water,

    the coil was made in copper but i was using 11250btu -per-sqft avg to my heating calculation which is a number recommend by the stainless steel quilted coil people - copper heat transfer is higher so the performance is a bit over the top to put it mildly ;)

    am using controlbyweb.com x300 stats, attached is a screen capture of all 8 at once - these stats allow me to send simple xml cmds from any application to get and set the stat's mode and values
  • Paul Pollets
    Paul Pollets Member Posts: 3,617

    you should...he's the real deal!
  • DanHolohan
    DanHolohan Member, Moderator, Administrator Posts: 16,283
    For those who don't know,

    Kal is America's other Mikvah Superstar. He and Moses do brilliant things together.

    And whenever Moses finishes a PLUMBING job, he holds up his arms and says, "LET MY PEOPLE GO!"

    Retired and loving it.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,483
    Mikvah help

    So would helping out with a mikvah problem be a mikvah mitzvah?
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • NYplumber
    NYplumber Member Posts: 503
    edited November 2013
    heat loos & dt

    Good evening wallies. Done a fair share of hydronics. Snowmelt to custom radiant to retrofits. Got a job to change a boiler supplying a private mikva. Has a one inch coil in the water. Would I do a heat loss like the ibr does on a pool? I have the surface area and all dimensions. Roughly 940 gallons.

    Also, how do I choose a dt?

    Lastly, does anyone have an engineering chart for copper pipe edr vs DT (accross the coil to the pool water) and internal flow of the coil to see if the coil can handle the boiler? This is a retrofit job.

    Thanks in advance.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    Load factors....

    Hey Moe, Happy Hannukah, and belated happy Thanksgiving..

    I can tell you the worst case scenario load/pickup factors, and some other limiting factors, but can't tell you the exchange factors for the copper coil. Maybe Moishe or Kal can help you there.

    The first most obvious question to ask is what was there, and how did it work?

    Next, limit on flow of a 1" coil is around 10 GPM for a non tube eating velocity.

    Next question, why a closed heat exchanger? Why not a potable rated water heater?

    As for pickup, if the room is maintained at 70 degree F (for example) and you want to raise the temperature of the water 35 degrees F to 105 degrees F, then the calculation is gallons times pounds times differential in temperature (assumed to be thirty here) for the energy required to heat the fluid up to the desired temperature. To that, you will need to add the conductive and convective losses, and the heat exchanger (if used) inefficiency and the appliance efficiency.

    Conductive loss is just like the losses through a wall. A over R times delta T . A being area, R value of the material containing the water and delta T being worst case scenario delta T.

    Convective loss off of the evaporating surface will be approximately 30 btu's per square foot per hour per degree F differential . Use worst case differentials to cover the loads.

    As it pertains to flow delta T, that is going to be a function of exposed heat exchanger surface area, and temperature differentials, which will change over time. You will have to select a DT for any software program to size the heat exchanger, and I always recommend keeping that number low. If you chose a large differential, it will work GREAT when the DT is large, but will fall short in finishing of the water temperature as the differential gets less. If you chose a low DT number, the HXer will work greater during the pickup.

    Adding up all of these load factors will tell you how big the heat source needs to be, but won't guarantee that the heat exchanger is capable of pushing that many BTU's into the water, so I'd go about it backwards. Figure out what the heat exchanger is capable of doing, and size the heat source to that, and everything else will be what it is, or as they say in the PC business WYSIWYG (what you see is what you get).

    It would probably also be a good idea to speak with the customer to find out what their expectations are. Under promise, and over deliver :-)

    Good luck, and let us know how it turns out and the performance you get.

    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.
  • NYplumber
    NYplumber Member Posts: 503

    Good afternoon. Happy thanksgiving to you too. Thanks for the reply.

    While gpm inside the pipe vs velocity is extremely familiar to me, the rest of the hx info hasn't set in yet. Spent a few hours last night going through many available engineering tables and graphs only to come out with more questions. All great info, just have to piece it together to form the puzzle.

    As for the water heater question, the water in the pool must stay in the pool. That leaves a few options to heat the water. Hx dropped in the pool, radiant walls and a few other creative options. In short the two waters should be separate.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840

    Why I am not an expert in Mikvah's :-) after I posted, I re-read Alan's original post and realized the issue associated with my remote direct water heating recommendation.

    The surface area of the copper bundle is fairly easy to calculate. You'd need to find a software program that could take all of the critical details into consideration, and I wouldn't know the first place to start looking for that.

    The Mikvah masters will eventually chime in I'm sure.

    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.