All vents on RVs are 14X14 whether power or not. Fantastic Vent says to not use a cover on their power vent. I have had a cover over my bathroom vent since I got the MH. At a rally we had 13 fans installed in various coaches and one of the fellows who came and helped the installer was a VP for Fantastic at that time. He put the cover back on and said their only concern was that some cut down air flow and people are disappointed then. Getting their lowest cost 3 speed fan has been great. Low speed will pull the door shut, medium will create a draft and High is for emergency use only. We rarely close the cover on that fan. The kitchen one has temp control and rain sensor so that one we don't worry about.