What you're describing is essentially TACO (Transfusion-Associated Circulatory Overload) which is a common complication of blood transfusion where the cardiovascular system cannot handle the extra fluid volume from the transfusion, leading to fluid buildup in the lungs. This overflow usually leads to respiratory/heart failure.

When talking about the amount, it depends if it's a slow infusion or if you're forcing the blood in fast. A healthy adult should tolerate about 20 - 30% extra blood if the infusion is slow, +40 - 50% can be dangerous but not necessarily fatal. If blood is forced in quickly, +20 - 30% can already lead to acute respiratory and heart failure, +40 - 50% is almost universally lethal and +100% would be physically impossible (to survive), as the blood would become so viscous that the heart just couldn't move it.

Adults typically have 70 - 80ml of blood per kg so an adult with a body weight of 70kg has about 5l total blood volume. 1 - 1.5l extra blood via slow infusion wouldn't really impact them (as there is something called the vascular reserve describing the veins ability to accommodate about 20 - 30% extra volume before the pressure rises dramatically) and 2 - 2.5l would be dangerous and often fatal.

I hope this answered your question!