Temporary Blockages in Radon Mitigation Systems Caused by Ice Jams

What leads to the freezing of radon vent pipes? 

In cold climates, it's common for radon mitigation systems to experience temporary clogging due to ice formation on the vent pipe connected to the radon fan. This issue arises from the inherent nature of radon systems, which draw damp air from beneath structural concrete slabs and crawlspace liners.

To elaborate, radon, originating from deep in the soil, enters homes. Radon mitigation systems work continuously by actively extracting radon gas from under concrete slabs, sump pit basins, and crawlspace liners. Since moisture vapor and other soil gases are also present in the soil, they are drawn up through the radon system. While this process offers several benefits such as reducing relative humidity, minimizing odors, and enhancing air cleanliness, the drawback is the potential for ice formation during cold winter months due to the extraction of moisture vapor.

A substantial amount of moisture is drawn from beneath a house, traveling upward, and released into the atmosphere through the vent pipe in the radon system. Typically, condensation forms directly above the radon fan and drips back down through the fan into the pipe beneath it. The fan consistently converts this liquid condensation back into moisture vapor and directs it upward through the vent pipe. Despite weather conditions, it's unavoidable for condensation to occur inside the vent pipe. If a radon contractor utilizes a gutter downspout instead of a 40-gauge PVC pipe, condensation drip becomes a more significant issue due to the lack of insulation in most downspouts.

If temperatures consistently drop below freezing, the condensation within the pipe can transform into ice. This occurrence is prevalent in northern regions of the United States and Canada, particularly on extended vent pipe runs exceeding 10 feet or when using metal downspout vent pipes, as previously mentioned.



How to prevent freezing in radon system vent pipes?

  • Remove or not install varmint guards, vent covers, critter guards, or exhaust caps. These areas naturally accumulate condensation, providing a conducive environment for ice formation. We advise allowing unimpeded airflow up through the vent pipe, as the outward flow of air makes it challenging for varmints and debris to enter the system, though not impossible. For most individuals, the advantages of preventing the system from freezing outweigh any potential drawbacks.

  • Avoid using uninsulated gutter downspouts for your vent pipe. While some may find gutter downspouts more visually appealing than PVC pipes, it is not a recommended choice due to poorly sealed seams and inadequate insulation, leading to increased condensation within the pipe.

  • Maintain the vent pipe as short as possible. Longer pipe runs tend to retain more condensation without complete clearance at the pipe's end. Shortening the vent pipe can be challenging since the US Radon Code (ASTM 2121 Guidelines) mandates vent pipes to extend above the lowest gutter line of the house. In contrast, Canada, acknowledging the potential for ice jams in their cold climate, explicitly states that vent pipes are not obligatory. Canada's radon mitigation system guidelines differ from those in the United States due to this specific concern. Unfortunately, diverging from this practice is not acceptable in the United States, and contractors may face fines for installing radon systems without professionally placed pipes.

  • Direct the condensation below the fan to reduce the risk of freezing. An option for diminishing condensation and minimizing the freezing hazard in exterior-mounted systems involves installing a tee pipe connection below the radon fan, rather than a standard 90-degree connector. One end of the tee fitting supports the fan, while the other end is capped with a small ¼” hole, directing the drained condensation toward the ground beneath the fan. A drawback of this approach is the formation of a water puddle below the fan in warmer months and a substantial ice icicle in colder months.

  • Using an electrical warming coil to heat the pipe. This involves wrapping the vent pipe with the coil and connecting it to an exterior outlet. While effective in certain situations with sufficient heat, the downside includes considerations of aesthetics and increased electricity consumption.

  • Allow for natural thawing. Many individuals opt to wait for warmer weather, letting the system thaw on its own. Recognizing that the hazards of radon exposure accumulate over extended periods, some people find comfort in tolerating slightly elevated levels in their homes for a couple of months. The decision to pursue this option is subjective, dependent on each person's comfort level with knowingly enduring higher radon levels.

Is the system still functioning to some extent even if it's clogged?

The answer can indeed be affirmative, albeit to a small extent. Through performance testing on partially or completely clogged systems, it has been observed that radon systems still exert a slight pull on slabs and crawlspaces even when obstructed. The extent of this functionality may vary significantly, and the performance is not considered ideal. As systems can operate differently, conducting personal radon testing is advisable to assess your specific levels.

It's important to note that radon mitigation contractors typically aren't held responsible for weather-related issues impacting the radon system. The system's performance is gauged based on the average radon level over a year, representing a 12-month period.

Are there alternative methods to maintain low radon levels during the cold months aside from utilizing a radon mitigation system? 

  • Enhancing Ventilation. Boosting ventilation involves introducing more fresh, clean air into a home or building. These systems, known as air exchangers (e.g., Heat Recovery Ventilator or Energy Recovery Ventilator), mechanically draw outside air, condition it, and circulate it indoors. These systems replace a portion of the indoor air and can be optimized for efficiency. Studies have demonstrated an average of a 50% reduction in radon gas and other indoor air pollutants in homes employing such systems.

  • Filtration. The filtration approach is straightforward and cost-effective. It's important to note that radon itself cannot be filtered as it is a noble gas. However, filtration can target Radon Decay Particles, which are byproducts of radon. These particles, when inhaled, are implicated in causing lung cancer by attaching to the soft tissues of the lungs.

    Effectively filtering Radon Decay Product (RDP) has been thoroughly validated. For this method, it is recommended to use a high-end air filter, such as the Breathe EZ Air Cleaner or another MERV 13+ filter. More information about this product can be found at The Breathe EZ Air Cleaner has undergone testing and has been proven to filter RDP up to 98%. It can be professionally installed without requiring any adjustments to your home's HVAC system ductwork.

    The primary step in filtering Radon Decay Product involves installing a MERV 13 or superior filter in your air handler, such as the furnace. The second crucial aspect is maintaining consistent air circulation within the home. Without proper air circulation, effective filtration cannot occur, leading to the presence of Radon Decay Product. Additional benefits of this type of filter include the reduction of dust, allergens, chemicals, viruses, and odors in the air. It's important to note that while Radon levels remain unaffected, filtering and eliminating Radon Decay Product can significantly reduce the risk of radon-induced lung cancer.

Who should I contact for help?

Get in touch with a local radon professional for expert advice on your system. Ideally, this could be the company that installed your system. Alternatively, consider contacting a member of Maine Radon and Environmental (, comprising certified and trained professionals. They will engage with you to devise an approach that caters to your needs and supports you and your family during the cold weather period.

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