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Sizing Hot water heaters?

RayHRayH Member Posts: 70
I need to figure the correct size Hot water tanks to install with an oil fired boiler for a 12 unit apartment complex.


  • SWEISWEI Member Posts: 7,356
    I posted this in the other thread
    Did it not provide a number you could use?
  • RayHRayH Member Posts: 70
    Not much help
  • RayHRayH Member Posts: 70
    I have 12 bathrooms w/showers & lav sinks, 9 kitchen sinks, 10 laundry
  • RayHRayH Member Posts: 70
    My thought is 2 120gal. tanks but I WOULD LIKE SOME TYPE OF FORMULA TO FIGURE THIS.
  • SWEISWEI Member Posts: 7,356
    In order to properly size a system, you need to know (or assume) flow rates for the showerheads, sinks, etc. and then apply diversity factors based on the number of units and use patterns. takes all of these into account so you know how much burner and how much storage you will need based on ASHRAE accepted numbers.
  • RayHRayH Member Posts: 70
    Thanks SWEI
  • SWEISWEI Member Posts: 7,356
    If you really want to cover your butt, get the client engaged in the process and have them sign off on the assumptions. If they do, you'll probably be selling them 12 new showerheads and a bunch of sink aerators.
  • SWEISWEI Member Posts: 7,356
    I should mention that getting the assumptions right is truly critical. We sized a system for a hotel a couple years back and I used the standard hotel math. All went well for 2-1/2 years. Then the hotel had a 100% occupancy conference event during February. Groundwater temps were at or near their annual low, and everyone staying there has to be at the same 8:30 AM meeting. Boom. No hot water. Went back to the ASHRAE Fundamentals as we tried to figure out what happened, and found that while the peak period assumption for a standard hotel is two hours, a convention hotel is assumed to be one hour. Makes perfect sense in retrospect.
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