Primary-Secondary Piping or Pumps in Series?

Alan (California Radiant) Forbes

hot_rod

1/2 and 1/2

Pumping at the expansion tank?

The least pressure drop is probably still across the P/S tees, so it probably will work to some degree. A close nipple between the tees would be of some help.

Alan (California Radiant) Forbes

I get tunnel vision and miss things. 

It will be interesting to see what the Caleffi gauge does when we start the system. Anyone interested in guessing?

hot_rod

there is a check valve in that 573 fill valve, but I think the gauge is downstream, so the pressure should jump above static fill when the boiler pump runs. Depends on what speed that pump is set at, I'd guess 6 psi or more added to the 12 psi static.

Zman

Primary/secondary sort of... I think the gauge will remain pretty stable. The pressure at the boiler will drop a bit. If it wasn't a firetube with a pressure drop similar to a bathtub, I would repipe it. If you run it on speed 1 things should be OK

hot_rod

What goes into a tee must come out of a tee, and vice versa.
So if the boiler circ is moving 8 gpm into the run of the tee, 8 gpm will go back up into the boiler.
Next would be to know the gpm of the heating loop. If it is exactly the same, more to the boiler, or more to the heating loop. Then you can calculate the blending that will take place at the tees

Alan (California Radiant) Forbes

@Zman is correct. I set the initial pressure high to get the air out of the system - 26½ psi - and the gauge is rock steady from initial startup through speed 3.
Unfortunately, I didn't have a gauge to screw into the hose bibb before the pump. If the pump creates a differential pressure, you would expect a pressure drop there, but it's hard to imagine.