Hello all, I've gathered lots of information thus far from this helpful forum, and thought I'd give a brief introduction of my set up along with a question. I just received my new 102kbtu (30kW) Kedel pellet boiler. I am in the process of plumbing it up with a 120 gallon pressurized buffer tank and keeping my old Pensotti oil boiler in parallel. I will have x4 zones including my shop plus a 30 gallon domestic hotwater heater. My first question has to do with expansion tanks. My rough calculations indicate I will need about 16 gallons of expansion tank for my system. When I was at the plumbing supply store they told me they had a 14 gallon system, and I was simply going to keep my existing 4.4 gallon tank in place as well. However, the woman behind the desk then suggested a 20 gallon tank that was actually a few bucks cheaper... so 20 gallon it is. Upon getting home, I remove the tank from it's box and realize it is actually a well tank called "Water Pro manufactured by Amtrol". It's a WP20 and states on the side it's not designed for operation above 140*F and max temperature is 200*F. Should I return this back to the plumbing store and get the 14 gallon unit rated for an expansion tank, or are these common tanks to use for larger hydronic units? Thanks for your advise!