We have a radon level of 4.9 in our unfinished basement. We hired a mitigator and he has been trying to mitigate it since April. We have two systems installed on the house and still can't get our number below a 4.0. We are getting ready to have a HRV system put on. Will this system help bring our number below a 4.0? We are moving and need to get our house on the market. Our real estate agent is telling us we will not be able to sell our home if we cannot get our radon level under a 4.0. Any advice would be great.