Inspectors tell me that about 40% of homes they test for radon in the Minneapolis-St. Paul area show levels above the accepted safe level of 4.0 picocuries per liter (pCi/L). Radon is the second leading cause of lung cancer (the leading cause for non-smokers) so it is something you should take seriously. Reuben talked about radon in a previous post, "How much radon does your home have?" Evidently the state of Minnesota takes it seriously as they now require that new homes in Minnesota be built with a passive radon mitigation system…a fan can easily be added later if elevated radon levels are found.
The most common form of mitigation is a system with a sub-slab pump and a vent pipe running from the ground beneath the basement through the roof, with a fan running continuously to expel radon gas.
An HRV system (Heat Recovery Ventilator, frequently called an air-to-air exchanger) can also reduce radon levels although more expensive and not usually installed specifically for this purpose. HRV systems are commonly used in newer, tight buildings. Tight buildings reduce energy costs but without adequate ventilation they trap humidity and pollutants (including radon) which can aggravate allergies and cause general discomfort and other health issues. Moisture damage to windows and other parts of the building shell can also result when humidity is too high.
An HRV system exchanges stale, moist, polluted indoor air (including radon) with fresh filtered outdoor air and helps keep energy costs low by preheating the incoming air in the winter and precooling the incoming air during the summer.
A home recently inspected for a client showed elevated levels of both radon and moisture in spite of an HRV system in place. It was discovered that the air intake vent was plugged, and the system needed to be adjusted and balanced to work at full capacity. Servicing brought the radon level down from 9.7 to 2.0, a significant change.
This points out how important it is to keep your HRV system cleaned and serviced on a regular basis…it can actually make a radon problem worse if it's not cleaned and professionally serviced regularly. Whatever system you use, keep it running continuously to ensure a constant degree of ventilation throughout the year.