I am doing an upstairs bathroom remodel that presents an opportunity to install a hot water recirc line. The bathroom is the farthest point in the house from the hot water heater and is currently the high point in the water system. Since I have a slab foundation the only return route is through the attic. I am able to access both ends to run the pipe but this route will move the high point to the attic. Does a 1/2" copper recirc line need an air release valve at the new high point or will the velocity of the water in a 1/2" pipe flush out what little air might accumulate?