I put in an exhaust fan for my eherms rig this weekend after dealing with the steam from by first brew using a bunch of window fans. Its an inline fan from Vortex purchased on Ebay. Its a six inch model rated for 449 CFM. For the ductwork I used 6" PVC drainage pipe. It works well becaust all the fittings are gasketed so you just slap it together and hang it. I do need to find something better for the hood, I just grabbed a square to round adapter at HD for now. Im also going to get a cap for the end that I can just take on and off as needed.
Mike
Mike