I Over Sized My Keystoker

Two expansion tanks in different locations is bad news. Pump away from expansion tanks, not towards. Pumping into an expansion tank causes the pump to pressurize it and decrease it's effectiveness. The pump also moves water from the suction side tank into the discharge side tank on startup causing greater system pressure fluctuations.

Ok to put auto air vent on boiler(s) and/or high points in pipes.

I would recommend moving air separator, pump and both expansion tanks to hot water supply side of coal boiler. Parrallel pipe expansion tanks to one point of connection to system at air separator.

While you are at it, I would think about changing piping between boilers to 1-1/4" just for good measure.

You can also tweak the controls on the coal boiler to produce hotter water to compensate for lower flow. Try upping the controls to 190/170 Deg. in colder weather.

I plan on repiping the coal as its own unit come spring and have it valved off from the system. Two completely separate systems with their own circulators. When I do this, you recommend having an air separator on each unit? Is there a way to just have one and have it available to both systems?

The expansion tank on the oil boiler is valved off. The keystoker installation instructions say to have the pump on the return to the boiler and the expansion tank where it is shown. Doesn't this go against what you just mentioned?

I've had the temps in the coal set to 190/200 and it still didnt keep the house to temp.

It looks like the reinstall should solve my problems.

Thanks for all the info.

Most boiler manufacturer's put the pump on the return and pump into the boiler. This is ok. The best air separation occurs after the water is heated and under the lowest pressure. Based on this, most hydronic speciality manufacturer's recommend putting the air separator after the boiler and the pump after the air separator, but putting the pump before the boiler and the air separator after the boiler works also. Always put the expansion tank on the suction side of the pump.

If you are repiping to parrallel boilers, pipe each boiler identical.

Attached are a couple of articles for you to ponder.