The US Environmental Protection Agency regulates emissions from residential wood heaters under the Clean Air Act through new source performance standards (NSPS). Additionally, the Agency has a public outreach partnership program where EPA works with Federal partners, States, Tribes, local air agencies, device manufacturers, retailers, and chimney sweeps to promote best practices about burning wood in home appliances. This program, Burn Wise, also provides information to communities about appliance change-out programs and educational material. Air quality modeling can provide useful information about the contribution of this sector to ambient particulate matter less than 2.5 microns in diameter (PM2.5) to support public outreach efforts. Photochemical grid models use state of the science numerical algorithms to estimate pollutant formation, transport, and deposition over a variety of spatial scales that range from urban to continental. Emissions of precursor species are injected into the model where they react to form secondary species such as PM2.5 and then undergo transport before ultimately being removed by deposition or chemical reaction. Photochemical model source apportionment estimates source specific contribution from primarily emitted PM2.5 and from precursors through the formation and transport of secondary formed particulate matter. This type of emissions apportionment is useful to understand what types of sources or regions are contributing to PM2.5 estimated by photochemical grid models. Photochemical transport model source apportionment is used to estimate the contribution of emissions from the residential fuel combustion sector to model estimated primary and secondary PM2.5. This is a national scale assessment done using emissions from the 2011 National Emissions Inventory version 1.5, which contains estimates of multiple residential fuel combustion groups: fireplaces, woodstoves, outdoor hydronic heaters, and outdoor recreational devices. Photochemical transport model estimates have a 12 km grid resolution, represent the year 2011, and do not include any projections to future years or quantify the effects of any specific control programs.