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Buffer tank piping

RPKRPK Posts: 68Member
edited October 2018 in THE MAIN WALL
How do you prefer to pipe your buffer tank? I’m installing a buffer on a new system with some fin-tube zones and some radiant floor zones. I would love to use the Caleffi buffer tank and pipe it using four ports like a hydraulic separator (see page 34 of Idronics 15 on hydraulic separation). I want to have a plan B in place in case there
isn’t room in the budget for the Caleffi tank, so I’m looking at using an electric HW heater (as I’ve seen described here in the past).

So a standard 1” MPT fitting will seal okay in the heater element ports?

What do you do about the 3/4” connections if 3/4 is too small, , just increase pipe size as soon as you leave the tank? I’m thinking being at 3/4 for just an couple inches isn’t such a big deal at the flows involved here. It seems like using larger ports might preferred where water is entering the tank to keep velocities lower and avoid too much mixing.

Which connections are preferred? I was thinking of boiler supply into top element port, boiler return into low element port. Remove dip tube and use the hot and cold connection on top for two supplies. Not sure where returns would be.

Would anyone care to share some pictures?


  • hot_rodhot_rod Posts: 11,393Member
    what kind if gpm flow rates?
    I use the element connections with 1” mip to 1-1/4 or larger copper adapters. A two pipe buffer works well with an electric WH tank

    3 pipe has some unique features but requires a multi port, more expensive tank. I’ll dig out some pics, download Idronics 10 on buffer tanks
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • hot_rodhot_rod Posts: 11,393Member
    Here are some options. I used a Lochinvar brand 6 gallon as it had multiple ports and I put a 4.5 kw element for electric backup in it also, used the controls that were already on the tank, 30A dryer plug behind to power it up.

    Increase small ports as quickly as possible and they do not add too much pressure drop. The pipes close to the tank need to be large diameter as those act as a hydraulic separator, 1-1/2 - 2" if possible.

    Top connections for air vent, temperature gauge, etc.

    The main difference with 2 and 3 pipe is the boiler can supply directly to the load without involving the tank. The tank charges when the heat load (gpm) is less than the boiler. When the tank is warm the boiler will not run until tank temperature is depleted, the load pulls from the tank via that close piping.

    With 4 port you are always flowing thru the tank. Pros and cons to each method.

    The 3 pipe adds one additional feature in that return is direct to the boiler, assures the coldest possible return to the boiler for highest efficiency, excellent for heat pumps, mod cons also. It does take a tank with multiple lower connections, harder to come by in small sizes.

    The control sensor for the boiler goes into the upper portion of the tank.
    The tank tells the boiler what to do, not the zones or wall thermostats.

    This Idronics issue was released before we discovered some of the uniqueness of 3 port from Mr. Manning, a GEO designer.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • RPKRPK Posts: 68Member
    Just rough estimates at this point, but 12-15GPM from the boiler, 10GPM max to the radiant floor and 6GPM to the high temp loop.

    Thanks for the pictures hot rod! So you removed the anode and diptube to use the top ports? What is that black manifold thing on the center port?

    So if the control sensor goes in the top of the tank... do you just jump R-W and let the boiler keep the tank charged at all times? Do the zones enable the system pump?
  • hot_rodhot_rod Posts: 11,393Member
    yes, remove anode and any dip tube

    Most boilers have a remote sensor in the installation packet slip it into or fasten it onto the tank

    The black device is an insulated safety group that we build, mainly for wood and pellet boilers
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
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