Primary loop to buffer tank - circ sizing for gpm

Dave Carpentier

(Upgrading from oil to gas boiler plus piping)

I used the Grundfos tool to plot my primary loop circ ( a 15-42 3-speed) vs the head loss in the loop.

The IBC boiler has a flow/head table, as does the Dirtmag. For the 1" pipe I used an online calculator for 8ft of equivalent pipe (buffer tank will be beside boiler and the main notable is the 3/4" port restrictions going in and out).

It looks like on Med speed, the primary loop would be flowing ~ 8.7 gpm , on Low it would be around 5.5gpm. The boiler's stated min flow rate is 2 gpm.

The secondary loops would be flowing anywhere between ~ 0.5 and 7 gpm I suspect.

It seems to me that, for normal day to day secondary flow, the circ will flush thru the buffer tank even on low speed.

I would like to reuse this 15-42 (recycling it from my existing oil system) but maybe it's just too fast ?

Can I help the situation by increasing the buffer tank delta, or turning down the Ramp on the boiler ? Introduce more head on the primary loop ? (a valve partially closed ?)

New system diag for ref