We recently had a high efficiency furnace put in. The old existing cold air intake remained as part of the former set up. Since this occured we have condensation issues along the piping. Our home is about 25 years old and not overly efficient (80% max.). In the past few years we replaced the windows, not the furnace and removed the gas water tank and replaced it with electric as we were told that we have "negative pressure" in the home. Not sure what that is or what causes that. We have heard that it is good to keep the cold air intake for air exchange and this some how helps with the negative pressure problem. The metal piping was replaced with insulated flexible piping and the run is much longer now, but it condensates where it is connecting with the cold air duct. We have been told that even if this is insulated it would then likely condensate in the duct . . . and so on. We would like to preserve the intake but don't know how to resolve the problem. Any ideas?