Air pollution levels in Ulaanbaatar, Mongolia's capital, are among the highest in the world. A primary source of this pollution is emissions from traditional coal-burning space heating stoves used in the Ger (tent) regions around Ulaanbaatar. Significant investment has been made to replace traditional heating stoves with improved low-emission high-efficiency stoves. Testing performed to support selection of replacement stoves or for optimizing performance may not be representative of true field performance of the improved stoves. Field observations and lab measurements indicate that performance is impacted, often adversely, by how stoves are actually being used in the field. The objective of this project is to identify factors that influence stove emissions under typical field operating conditions and to quantify the impact of these factors. A highly-instrumented stove testing facility was constructed to allow for rapid and precise adjustment of factors influencing stove performance. Tests were performed using one of the improved stove models currently available in Ulaanbaatar. Complete burn cycles were conducted with Nailakh coal from the Ulaanbaatar region using various startup parameters, refueling conditions, and fuel characteristics. Measurements were collected simultaneously from undiluted chimney gas, diluted gas drawn directly from the chimney and plume gas collected from a dilution tunnel above the chimney. CO, CO2, O2, temperature, pressure, and particulate matter (PM) were measured. We found that both refueling events and coal characteristics strongly influenced PM emissions and stove performance. Start-up and refueling events lead to increased PM emissions with more than 98% of PM mass emitted during the 20% of the burn where coal ignition occurs. CO emissions are distributed more evenly over the burn cycle, peaking both during ignition and late in the burn cycle. We anticipate these results being useful for quantifying public health outcomes related to the distribution of improved stoves and to identify opportunities for improving and sustaining performance of the new stoves.