There would be an increase in the amount of Radon pulled out of the ground. Usually the way an HVAC system is set up is that you have the filter, then the evapo

There would be an increase in the amount of Radon pulled out of the ground. Usually the way an HVAC system is set up is that you have the filter, then the evaporator coils, then the fan, then the ducts to the rest of the building. To heat or cool the air the tubes would need to be placed before the evaporator coils or it would just be wasting energy instead of saving energy. This also puts it before the fan. Everything before the fan is at a negative relative pressure and everything after it is positively pressurized. Presumably those tubes aren't perfectly sealed so the negative pressure will draw in a tiny bit of Radon from the ground. You could flip things around and move the fan to right after the filter and before the tubes and evaporator coils, I'm not 100% sure why that isn't normally done but all of the residential HVAC units I'm familiar with are done this way so there's probably a reason.