Hot Water Recirculating Loop
Travis, re my post yesterday to your question, I assumed that you were speaking of an open system, i.e. domestic hot water recirculation system. If so, my post stands as is. If you are speaking of a closed system however, the air must be removed as you fill the piping system since there will be no additional water added that can "absorb" the air trapped in the loop. This can be done with a small manual valve located at the highest point, or with an air removal fitting that is designed for this [a pricey way of doing this for something so seldom used, only if you drain and refill your piping[.