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System ghosts

Tim R
Tim R Member Posts: 5
I have just completed an oil fired boiler system installation. Primary/secondary piping, pumping away. Ground floor -boiler, indirect HWT and 2 low temp zones. Second floor 3-high temp baseboard zones.The primary loop uses 1-1/4" copper, a UP15-42 pump and closely spaced tees 5"-6"c-c. The supply and return piping to the second floor zones incorporates "underslung tees" and UP15-42 pumps. I was hoping to eliminate the ghosts by using the drop below the main before rising concept but to no avail. To cure the problem I will probably have to install spring checks on the supply risers 18-24" from the pumps.
With closely spaced tees there should be no pressure differential established in the zone to cause flow. The underslung tees should create the thermal traps to prevent migration. The Buderus boiler has a return fitting that reduces the primary return to 1" pipe size. The primary pump is capable of pumping 14gpm thru 1-1/4" pipe. Could the reduction in pipe size at the boiler return cause flow thru a second floor zone? Would a different pump (2 or 3 speed) have any effect? Would increasing the underslung portion of the S&R piping from 3/4" to 1" create a more effective thermal trap?


  • hot_rod
    hot_rod Member Posts: 21,858
    I've never

    had much luck with thermal drops. I even built a 6 foot deep one once!

    A quick, simple try would be to replace the 15-42 with a 15-58 Super Brute. This has an intergal check, properly sized, and may be all you need.

    However you may need a check on the return also. Hard telling, not knowing.

    As Tony Conner always advised, usually a line sized chech is oversized and may cause chatter. Depending on flow, a 1/2" may be fine.

    Use a check with a soft seat. Watts and other have checks with EPDM or teflon flapper and seats in case the fluttering gets to going.

    Still better to size right and avoid flapping in the breeze. Let us know what works.

    I suspect there are many of these ghosts at work in hydronic systems. Yours was bold enough to be noticed. With radiant slabs they are very subtle, and often present themselves as high fuel bills :)

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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