Typically an ERV is the last resort for Radon Mitigation as the installed systems can be expensive and have limits on reducing Radon levels.
This is the go to option when a home does not have suitable sub slab conditions to allow an ASD system to properly move gasses underneath the concrete slab or for a home with an inaccessible crawlspace.
The ERV system reduces the Radon levels by “dilution”. The system is installed with the use of a series of duct work that delivers/ introduces a small amount of fresh air into the home as it removes a small amount of the stale air containing the Radon Gas. Therefore, diluting the air containing the Radon Gas.