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Commercial water heater sizing help

STEAM DOCTOR
STEAM DOCTOR Member Posts: 2,160
edited September 24 in Domestic Hot Water

Hi. I need to replace a water heater in a men's dormitory. Storage tank type only. Natural gas. 9 showers and three average sized commercial washing machines. Info coming from building manager. Current water heater is 100 gallons and 270,000 BTU. Just looking for any sizing guides or information or help. Thanks.

Comments

  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,160

    Not uncommon for all showers to be running at the same time. Or close to all showers.

  • hot_rod
    hot_rod Member Posts: 23,108

    is the current tank adequate?

    Water heater manufacturer have commercial sizing guides on their website

    Check to see shat shower heads they use, for actual flow calculations

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,160

    Current water heater is adequate. Let's assume 2.5 gpm.

  • Larry Weingarten
    Larry Weingarten Member Posts: 3,563

    Hi, You might be able to downsize the heater by installing 1.5 gpm showerheads. A simple rule of thumb is 70% of shower water is hot. Average shower length is eight minutes. Average tank withdrawal before cooling is 70%. So, nine showers at 1.5 gps is 13.5 gpm… times .7 is 9.45 gpm, times eight minutes is 75.6 gallons, divided by .7 is 108 gallon tank. Now if you add in the makeup provided by that burner, it's no wonder the tank is adequate 😀

    You could just replace the tank with the same size, and/or also replace the showerheads to save costs for the owners.

    Yours, Larry

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,157
    edited September 24

    I have always liked A O Smith commercial tank sizing guide available here

    http://www.hotwatersizing.com/ Select the type of building, Apartments, Hotel, Industrial, etc. the nit will have a form to fill in the blanks like the GPM if the shower head, Laundry needs, and the like.

    After you fill in all the necessary info, it will tell you what AO Smith offers to do the job including tank size, burner size, etc. With that info you can select any other brand that has similar specifications.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    GGross
  • jumper
    jumper Member Posts: 2,384

    Many disapprove but I recommend multiple heaters in series. We can also chew the fat concerning staging. How about setting upstream heater hotter? Counterintuitive? Only when upstream cannot service the load will second heater fire. Is it worth the expense to pipe valved off bypasses for each heater? That prevents a no hot water situation. Usually I see the opposite: parallel heaters with no valve on output.

    Larry Weingarten
  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,160

    Thanks for all the info. Spoke with several manufacturers today. Got some good info. I would love to be able to put two smaller heaters in series. But there is simply no room for two heaters

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