@JimboSaturn From personal experience I can tell you that any flood water that ends up on the bathroom floor will end up inside the burner unit of your furnace before it even starts to migrate out into the hallway on your main level.
The water will end up flowing down the hot air register which is located on the bathroom floor and which is also the lowest point on that floor where a floor drain would normally be located if one were installed.
Because that floor register is below the height of the door sill leading into your bathroom, a bathroom flood would go undetected until the water ended up inside the burner unit of the furnace. This is because the water would go down the register before it could get deep enough to climb over any door sill or carpet edge.
@swirlie I don't ever really have a problem with my toilet overflowing. In such cases, when I notice, it's not draining right, I turn off the water to the toilet and then use the plunger. It has never got to the point where the water overflows that much.
