Abstract: An improved apparatus for introducing steam into an airstream in heating, ventilating and air conditioning system includes a supply header, steam dispersing structure and structure for collecting condensation from the steam dispersing structure. The supply header is adapted for connection to a source of steam and is preferably elevated with respect to the return header, so that condensation in the supply header and steam dispersing structure is forced into the return header under the influence of steam pressure and gravity. One embodiment of the invention presents a unique modular design whereby the steam dispersing structure can be quickly connected and disconnected from the headers. This allows the apparatus to be broken down and assembled on site, which simplifies and reduces the expense of installation.