One of the mitigation approaches available is Air-Exchange. Think of this-The solution is dilution. Heat Recovery Ventilation (HRV) systems are considered for a variety of reasons. Some homes have unusual conditions under the basement floor or have crawl spaces that are inaccessible. Some homes do not have a solid concrete slab where an SSD could be used. Some homes are sited and constructed in a way that make a SSD system unviable. For others it is a decision driven by aesthetics. How they work: Air is drawn into the house at the same rate as air drawn out of the house. Much of the heat energy in the exhaust air is transferred to the fresh air coming in. The air exchanger dilutes radon by combining it with outside air. It should be understood that this exchange of air approach has limitations due to the efficiency of the system. The transfer of energy from the warm interior air to cooler outside air in winter months results in a net heat loss. Additionally, in summer months the hot humid outside air being brought into the house will result in a warmer/more humid interior environment.