Adequate vacuum relief on steam jackets is essential for proper operation. As steam valves are closed during a heating cycle, existing steam inside the jackets condenses and drain to condensate traps. This phase change causes a vacuum to be formed inside the jacket and imposes harmful stresses over time. By installing vacuum relief devices before the condensate trap, air can be drawn into the jackets to relieve any vacuum that could have formed. This function is especially important after a heating cycle is complete, when the steam valves will remain closed for an extended period of time with steam still in the jackets. With the possible addition of air into the jackets, all the more importance needs to be given to incorporating thermostatic air vents at the condensate trap as well. This vent will expel any air that could be in the jacket during startup. Any air trapped in a steam jacket will insulate the vessel from steam contact, drastically minimizing heat transfer.