Forced-air HVAC can move radon-contaminated basement air through the entire house. Properly designed HVAC and mitigation systems work together; the on-site assessment evaluates both.
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Forced-air HVAC distributes the indoor air pool throughout the home. If the air handler sits in the basement (typical in Cincinnati pre-2000 housing), and the basement has elevated radon, then radon-carrying air gets distributed to every room serviced by the duct system. Upper-floor bedrooms in this configuration test almost as high as basement spaces. Heat-pump systems and high-velocity systems behave similarly. Conversely, mitigation systems coexist with HVAC fine when designed together; the mitigator confirms during the on-site that the mitigation suction does not negatively pressurize the home enough to back-draft any natural-draft combustion appliance (water heater, furnace) sharing the basement. Combustion-safety testing (CO and draft measurements) is part of the install if the home has natural-draft equipment. Cincinnati HVAC retrofit consideration: when replacing a basement air handler with a high-efficiency unit, ask the HVAC contractor to coordinate with the radon mitigator if a system is already installed. The new equipment's air-pressure profile may differ from the old, and minor radon-system tuning (fan speed adjustment, manometer recalibration) may be needed. Both visits combined run 1-2 hours and prevent post-install surprises.