Transport of radon in indoor air is almost entirely controlled by the ventilation rate in the enclosure. Since air pressure is usually lower inside houses than it is outside, the home acts like a vacuum, drawing radon gas in through cracks in the foundation or other openings such as ventilation systems.[108] Generally, the indoor radon concentrations increase as ventilation rates decrease.[1] In a well ventilated place, the radon concentration tends to align with outdoor values (typically 10 Bq/m3, ranging from 1 to 100 Bq/m3).