When we install a radon-mitigation fan and most of its exhaust system piping inside a home's attic or attached garage, it's called as you might expect, an indoor mitigation system.
The primary benefit of an indoor system is cosmetic. The only thing that can be seen from the outdoors is an exhaust pipe protruding from the roof (12"+ by code), nothing more obtrusive than a plumbing stand pipe. But this pipe can be an issue. If anyone other than the original roofing contractor puts in the hole through the roof for this pipe, the roofing labor warranty may be voided. If the roof is newer, it's always best to get the roofer's approval in writing before moving forward, or even have him do the roofing work involved so the warranty is not effected.
Other disadvantages of indoor mitigations are related primarily to noise and condensation. As the fan is ordinarily sited in a garage or house attic, there's a good chance of hearing the system running... especially at night. There's no way to predict how the noise will carry through the home's wood joists, roofing or drywall.
can also be a problem. The system's exhaust pipe carries the ground
gasses out at an ambient temperature of 50 degrees. That can mean
sweating within the pipe in the winter which rolls back through the
system, and externally on the pipe's surface in the summer when heat and humidity
rise. This can cause dripping from the pipe which can be a nuisance,
especially in a garage. Run above a ceiling, it can damage drywall or plaster.
What's more, indoor systems can be more expensive because they typically require more materials and workmanship. If fan servicing is required, someone will have to be home to allow entrance to the house and fan access. And because they typically involve more piping than outdoor systems, there's more resistance to the fan. Theoretically, the greater the resistance, the lower the performance of a system.
It's because of these drawbacks that only about 10% of our installations are indoor systems.
Like any radon-mitigation system, an indoor installation must comply with plenty of protocols and codes. For instance, EPA/ASTM protocol demands that the fan be in a non-livable space (typically the garage or house attic; the basement is off limits). The exhaust discharge through the roof or siding must end at least 10' off the ground and at least 2' above any window.
If there are second-story windows, the exhaust must be at least 10' away from any window that can be opened. Electrical codes also mandate that an electrical shut-off be provided within 6', or arm's length of the fan. Building codes further require a fire-collar on the piping when it runs from the house to the garage, or if there is a garage ceiling, where the pipe goes through the ceiling to the attic. This is to prevent fire from traveling up or down the PVC pipe from one area of the house to the next should a fire break out.
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.