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Water Tanks on Roofs?

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Zman
Zman Member Posts: 7,614
in Radiant Heating

I have always noticed water tanks on the roofs of buildings in Boston and NYC. What purpose do they serve?

"If you can't explain it simply, you don't understand it well enough"
Albert Einstein

Comments

  • mattmia2
    mattmia2 Member Posts: 16,962

    the pressure to get the water to the top of the building is more than the main pressure so they pump it to a tank on the roof and feed the building from that.

    it can also be done with booster pumps.

  • Jamie Hall
    Jamie Hall Member Posts: 27,434

    They may also serve fire protection. Either way, you don't have to size your booster pump and service pipes for the peak load — just big enough to pump the average water use per day up there, with some reserve.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pecmsg
    pecmsg Member Posts: 7,124
    edited May 1

    city water pressure won’t lift that high. Pumps are used to lift it up then gravity delivers to the building.

  • Jamie Hall
    Jamie Hall Member Posts: 27,434

    I might add that some very tall buildings may have tanks on intermediate floors as well. Others will use pressure reducing valves.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    pecmsg
  • Mad Dog_2
    Mad Dog_2 Member Posts: 8,581
    edited May 1

    For the last Century and change, they've been assembled on the roof with wood slats like a barrell which are held in place with heavy duty straps. They leaked for a day or two until the wood joints swelled up. They have a large ball Cock much like a toilet tank.

    More recently they use Stainless steel. In NYC the two companies that have been doing them forever are Rosenwach and Isseks. Mad Dog

    Consulting by Mad Dog & Matt Jr.
    HVACNUT
  • Mad Dog_2
    Mad Dog_2 Member Posts: 8,581

    Average NYC Street water main pressure will usually be good up to 4 stories max, thus roof tanks

    Consulting by Mad Dog & Matt Jr.
  • Steamhead
    Steamhead Member Posts: 18,567

    IIRC many of those tanks had steam coils to keep them from freezing. These ran off the steam boiler that heated the building. Makes things tricky when sizing a replacement boiler………

    All Steamed Up, Inc.

    Baltimore, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting

    PC7060

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