This work examined window/door opening as means of bedroom ventilation and the consequent effect upon occupants' sleep, using data from 17 healthy volunteers. Bedroom CO2 level, temperature, and relative humidity were measured over 5 days, for two cases: open window or door (internal, bedroom door), and closed window and door. Participant filled questionnaires and sleep diary provided subjective measure of sleep quality. Actigraphy objectively monitored the participants during sleep. Additionally, a FlexSensor, placed under pillows of participants, detected movement during sleep. Average CO2 level for the Open conditions was 717 ppm (SD = 197 ppm) and for Closed conditions was 1150 ppm (SD = 463 ppm). Absolute humidity levels were similar for both conditions, while Open conditions were slightly cooler (mean = 19.7 degrees C, SD = 1.8 degrees C) than Closed (mean = 20.1 degrees C, SD = 1.5 degrees C). Results showed significant correlations (P < .001) between actigraphy data and questionnaire responses for: sleep latency (r = .45), sleep length (r = .87), and number of awakenings (r = .28). Of all analyzed sleep parameters, questionnaire-based depth of sleep (P = .002) and actigraphy-based sleep phase (P = .003) were significantly different between Open and Closed conditions.