The paper reports the results from a three-phase study characterizing and modeling particle and organic emissions from unvented kerosene space heaters, a major source of indoor air contaminants. In Phase I, emissions from 12 heaters covering a range of design types and Btu ratings, were evaluated. Aerosol mass, size distribution, extractable mass, bioassay, and trace element content, as well as conventional gas (CO, NOx, etc.) measurements were made for all the heaters tested, while VOCs and semivolatiles measurements were made for a subsample of the heaters. In Phase II, a detailed characterization of particle and organic emissions for four heaters was performed. Two of the heaters subjected to the detailed chamber testing in Phase II were then used in Phase III, which consisted of a series of heater runs in the EPA test house in North Carolina. The test house experiments were designed to validate model predictions based on the chamber studies in Phase II.