When we install a radon-mitigation fan outside of the house, it's called (not surprisingly) an outdoor mitigation. About 90% of the systems we currently install are sited outdoors; we take great pride in custom-designing them to fit with each home's design elements.
The primary advantage of this approach is that it puts most fan noise outdoors. But condensation can also be an issue: Because the exhaust system eliminates ground gasses at an ambient temperature of 50 degrees, these pipes can sweat and drip internally in the winter and externally in the summer. By locating the system outside, this is no problem.
Outdoor systems also require less in the way of materials and workmanship than their indoor counterparts, which typically makes them less expensive. They are generally shorter in total length, minimizing resistance; theoretically, the lower the resistance, the better the system's performance. Finally, if there's ever a problem, the system can be easily serviced even if the owner is not at home.
Like any radon-mitigation system, outdoor installations must meet strict protocols and codes. EPA/ASTM protocol demands that the fan be sited in a non-livable space, with the exhaust ending at least 10' off the ground, and at least 2' above any windows. If there are second-story windows, the exhaust must be at least 10' away from any window that can be opened, or again, 2' minimum above those also. Electrical codes also demand that an electrical shut-off be provided outdoors, within 6', or arm's length, of the fan.
System freezing is a reality… but happens rarely. Typically, it would happen to a system less than four months old, at outside temperatures starting about 5 below zero, sustained for at least a couple days. The reason new systems are susceptible to freezing is due to the sub-soil humidity being at higher levels than older systems. It typically takes about four months to dry a basement floor (slab) out, as well as make an impact to the sub-soil humidity levels. Once this period is over, system freezing typically never happens.
Where and why do systems freeze?
Radon systems discharge 50 degree (F) soil gas temps at an average of about 100CFM. When this gas has more humidity in these early months, this humidity gets discharged into the frigid air temps. When this happens, this humidity turns to snow and ice particles. These particles accumulate on the discharge pipe’s exit point, and can clog the discharge’s opening. The discharge typically stays frozen until outside temperatures reach about 15 degrees and above. Once this happens, the 50 degree gas temps melt these clogs and the system returns to operating properly.
System freeze-ups potentially (but rarely) happen to any newer radon system, no matter where it’s located. Since it happens at the discharge point, the system can be located indoors or outdoors with exhaust piping made of metal or plastic. Increased sub-soil humidity levels and / or low discharge rates (CFM) are the main reason for freezing due to water accumulating at the discharge point. A frozen system typically never lasts for more than about a week, typically never happens more than once to any system, doesn’t cause system damage, and typically doesn’t happen to systems having run more than 4 months.