I weighed the window on a scale and it came to 12 lbs. Would option A be correct? Assuming the 2 balances split the load.
You wouldn't split the load for this balance, our stamp ratings are based on 2 balances per sash. The A option can only carry 5 through 10 pounds, which would be too weak for a 12 pound sash. Looking at the next one up, B can carry a sash weight of 10 through 14 pounds. That would be the one I recommend.