THey installed a fan on the flues? There are power vented appliances, but I'm not familiar with the need or desire to add an exhaust fan in the flue for appliances that aren't designed for it. Plus, I don't particularly like that the flue size gets smaller at the inlet to the fan. All of this may be okay, but strikes me as a little flakey. Was this installation inspected? All combustion devices produce water vapor as part of the process, normally, the gasses stay hot enough to prevent condensation if installed properly unless it is designed specifically to condense (some are, but don't think yours are). I'd take a look at the manufacturers' installation instructions and see if this is an allowed installation method.