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Reversing the P/S connections?

Timco Member Posts: 3,040
So typical P/S shows the boiler return pulling return water first, then the supply dumps into the flow last and of course there’s some mixing of supply into the return. When I tied my CI oil boiler into my piping I reversed that so the supply hits the return water first and that mix is sent to the return and manifold supply and all flow goes the same direction at the tees. This seems to work great now that I’m on oil waiting to set my new LP tanks. Am I right that this will keep the return temp up?
Just a guy running some pipes.


  • hot_rod
    hot_rod Member Posts: 21,878
    Yes there are two ways to pipe P/S, direct or reverse injection mix. It determines where the mixing point occurs.

    Reverse injection was helpful sometimes to run the injection circ up curve, instead of at it's lowest speed. Early on the circ would sometimes fail to start at low modulation. Eventually they changed the logic so the injection circ always started at 100% then ramped down to required flow.

    Here is how tekmar explains it, in this 2000 era doc.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream