• Morgan Beall

Ventilation, Fresh Air, Radon Mitigation - What Could Go WRONG?!

One of the most common issues with mold or adverse indoor air conditions I find are related to terribly installed or misguided understanding of forcing outdoor fresh air into a home for the purposes of Radon mitigation. The concept for Radon mitigators (contractors) is really simple, you bring in outdoor air to dilute the indoor air thus reducing Radon concentration within the indoor environment. This is almost always done by installing an exhaust fan and reverse it to pump outdoor air into your air handler (HVAC system). The reason for connecting to the HVAC system is because there is a thing here in Florida and the subtropics called humidity. This happens only if the contractor understands this and I often find a vent just forcing outdoor air into the indoor air without being processed by the AC. Both methods are still very wrong and can cost the homeowner tens of thousands of dollars. Why you ask? Well when you force outdoor air into the HVAC system the HVAC system works much harder to process both humidity and temperature because you are basically trying to condition ...Florida! Your HVAC system will have a life span about half or even a third of what it is suppose to last. Similarly, when you force air into the living space of the home you are doing the equivalent to leaving all your windows open. Much like the previous method mentioned you basically increase the home's interior heat load and moisture load causing the HVAC system to over work. Both methods will ultimately lead to varying amounts of mold growth due to dew points and humidity levels reaching unmanageable levels within the interior living space. Many inspections of these conditions I have conducted over the years have lead to the discovery of significant mold growth and property damage. So mitigate Radon if your solution for Radon will lead to a new problem. Well, we can start by mitigating correctly by using real building science rather than the contractor status-quo or the State Of Florida's complacency with simplistic solution by supporting the cheapest methods. A sound method either to mitigate Radon or for creating good air quality within a home is to use a HEPA filtered independent whole home dehumidification system that will process the moisture and filter particulate before it enters the home and/or HVAC system. This method will remove the majority of the moisture and outdoor particulate before it creates issues within the home allowing your HVC system to do the rest of the work. There is still an issue however. You now have to deal with the heat from the outdoor environment. This is why in any situation with Radon mitigation your should hire a licensed HVAC contractor to ensure your HVAC system is balanced and mechanically improved to manage the higher temperatures and to correctly install the fresh air system (independent dehumidifier). When you add this or similar systems you are creating a different pressure pattern in the home called 'positive pressure'. To sum up my opinion and my concern is that in any situation you are changing the dynamics of the building's or home's engineering/HVAC system environment you need to hire a professional with the appropriate experience. Too often inexperienced or complacent Radon mitigators have caused more harm than good. I have added a few images to this article showing the results of the reverse vent radon mitigation system. This is the worse case scenario and can vary structure to structure/home to home.


This image is of the supply duct containing visible mold growth. It was found that the majority of the supply ducts (cold air ducts) contained visible mold growth due to conditioned air mixing with outdoor unconditioned and humid air resulting in condensation inside the ducts and insulation.













This image shows the surface mold growth on the majority of the HVAC Utility closet wall surfaces due to the mixture of the outdoor air and the indoor air. The system could not handle the higher temperature and moisture from the outdoor environment and caused conditions conducive to mold growth in localized areas including the surrounding wall cavities as the remediation efforts uncovered during the removal of the affected drywall.
























The mixing of the outdoor unconditioned air from the Radon mitigation system with the indoor conditioned air resulted in a temperature inversion (mixing of the two air masses creating high dew points and condensation) leading to elevated humidity and moisture impact at the points of the mixed air. The image above shows mold growth on the drywall under the metal supply vent cover position and within the supply duct box. Elevated humidity in this case emitting from the air handler reached 80% relative humidity and with dew point temperatures in the 70 degrees F (Should never exceed 60% RH and 62 degrees F dew point). Similarly these attributes can be identified when you see mold growth on metal supply vent covers like in the image below. If you see this in your home you likely have an issues with mixing of unconditioned air (roof cavity/outdoor) and indoor conditioned or cooled air.


If you are having similar issues, have additional questions regarding this topic and/or any other concerns with indoor air quality please give us a call at 239-940-0433.


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