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sizing domestic hot water system

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  • JBW_2
    JBW_2 Member Posts: 67
    sizing domestic hot water system

    Hey all,

    I am planning on installing a domestic hot water system using a boiler and indirect hot water tank.
    I have always gone based on the procedure of 10,000 btuh per unit/flat and 10 gal storage per unit/flat.

    i.e. for 20 unit apartment building, I would need 100,000 btuh and 200 gal of storage.

    Does anyone have another sizing approach - i am planning on using the buderus condensing boiler and one of their indirect water heaters. Please outline calculation steps or lead me to a good online resource.


    JOsh W
  • JBW_2
    JBW_2 Member Posts: 67
    dhw sizing

    i meant 200,000 btuh not 100,000 btuh.
  • tim smith
    tim smith Member Posts: 2,752
    Sizing dhw for multi units

    I have used the AO Smith sizing charts for 20+ years, never failed me. May be a little on the heavy side but better heavy than light. Tim Find AO Smith rep and get full catalog, they have all the different application sizing charts in it. PS, I never need more than about 80 gals storage & 180000 btu for 20 units unless of 2+ bedrooms with more than 2 people per unit.
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