I am wondering what most people are doing - tieing ERV/HRVs into the H/AC ducting or using dedicated ducting. It seems to me that with such small air flows, one can never properly balance where the fresh air goes - to bedrooms and where the exhaust comes from - kitchen and bath, when the ERV/HRV is tied into the ducting network of an H/AC unit. But... if using an indpendent ducting network, what (multistory) house has enough space to run two ducting systems unless one uses Zehnders with their 2" ducting distribtuion system. In looking at the installation instructions, it seems that most manufactuers assume the ERV/HRV will be tied into the H/AC ducting network either on the supply or return side. Here in CA, we have very strict requirements for H/AC ducting not to leak more than 5%, yet if an ERV/HRV is spliced into the network, it introduces many more opportunities for leakage. Furthermore, if the ERV/HRV is a "Return-Return" tied system, the H/AC fan must operate, which has been shown to kill the energy efficiency of the system as those motors are huge compared to the built in ones for the ERV/HRVs. So, it seems wierd to me that ERV/HRVs are ever tied into the H/AC ducting for distribution, but yet that seems like the only realistic (reasonable) option.