There are times when an increase in exchanger surface is desired to upgrade a system's heat transfer capability. The design modifications that are described in this chapter provide benefits, where they can be used, because they allow a system to be kept on-line longer as surface is manufactured; the time during which units are off-line to make changes will be minimal. It should not be assumed that less work is involved. Rather, most of the work can be done while the system is operating. The changes suggested will not normally increase an exchanger's cooling or heating capability by more than 50% because of existing nozzle flow limits and pressure drop constraints. The exception is double-pipe units, whose capabilities can be increased by adding units in series or parallel.