Expansion Tank Question

I have a crown boiler that is about 8 years old model # ABF-175SPD. The expansion tank went but I'm not exactly sure what size tank I should buy to replace it. Does anybody have experience with this type of boiler?

Your expansion tank isn't sized based on the boiler it's sized on the amount of water in the system. Your expansion tank should beable to absorb upto 4% of the volume of the system (give or take).

It's probably a 2 or 4 gallon expansion tank if this is a residential house.