Pressurization uses a fan to blow air into the basement or living area from either upstairs or outdoors. The goal here is to create enough pressure (positive pressure) at the lowest level indoors, such as in a basement, to prevent radon from entering the house. The effectiveness of this technique can be limited by house construction and climate. In order to maintain enough pressure to keep radon out, the doors and windows at the lowest level must not be left opened, except for normal entry and exit. Blowing air out of the basement to reduce radon levels, although seemingly a good idea, might actually increase the flow of radon into your home. As you blow air out, a vacuum effect is created (negative pressure) which will cause greater influx of radon into your basement from the surrounding soil.
Another form of ventilation is natural ventilation, which is achieved simply by opening doors and windows at the lower levels of your home. Natural ventilation mixes outdoor air with the radon contaminated indoor air, thus reducing overall radon levels.
There are some obvious drawbacks to both of the above techniques. Once you close your windows and doors, or turn off your fan that blows air into your basement, radon concentrations most often return to previous values within about 12 hours. Furthermore, as a result of more outdoor air being introduced into the home, you might see moisture intrusions, loss of conditioned air, and energy penalties, particularly during the winter months.
Consequently, both of these techniques are regarded as only temporary approaches to radon reduction and should only be considered after the other, more-common techniques (such as sub-floor mitigation) have not sufficiently reduced radon levels.
Another form of mechanical ventilation can be accomplished by installing a heat recovery ventilator (HRV), sometimes referred to as air-to-air heat exchanger. HRVs ventilate by introducing outdoor air while using the heated or cooled air being exhausted to warm or cool the incoming air. The advantage of an HRV system over other ventilation techniques is that besides supplying balanced ventilation, a HRV will reduce the energy penalty associated with providing more ventilation to a home. As an added benefit, an HRV can improve air quality in houses that have other indoor pollutants.