Diagram

looking for feedback on my diagram. doing a ton of reasearch. do I have to add a second expansion tank to this system, or since it will be in series with my oil boiler, will the one do?

Do you have to no
Should you yes
Your diagram shows the rad I assume that a raditors so you all ready have a large amount of water in your system.
You are probally adding 20 plus gallons of water to the system with the new boiler.
I would install a air scoop with a exp. tank and a air eliminator( vent) just before the 90 that facing the down.
BDD

Between the TEE on the recirc loop and the 90*? Maybe it might be better before the TEE, it will scavange air even during no heat call from the recirc loop.

good stuff - so it seems for not being much of a heating guy, my diagram is pretty close. is there some type of formula for how big the expansion tank needs to be? the one I have on the system currently is quite large, but yes I am adding 25 gallons of water with the new boiler. more questions - should the circulator be on the supply or return side? seems like there is some debate on that one. as far as sizing the new circulator, should I just use the same excact one that is on my oil boiler currently?

Use this site to size your system

http://www.amtrol.com/sizing.htm

ssupercoolss wrote:should the circulator be on the supply or return side? seems like there is some debate on that one. as far as sizing the new circulator, should I just use the same excact one that is on my oil boiler currently?

I would stick with the same make and model. As far as where, just match your current setup and let the debate rage on as it works fine either way. If you are anal retentive, put it on the supply side as current theory dictates.

I would put the 2nd tank in, but if you don't at least put the plumbing in for one.

Easier to screw on a tank and open a valve then have to open up the system mid-season.