I have a question. I’ve been trying to Google this and no one seems to have the same problem. I have Avast 2015 and would like to exclude some files that I know are false positive, but when I go to settings, there is no antivirus tab or exclusions list anywhere. Why is that?
menue / setup / exclusions … 
Go to “Settings” → “Active Protection” → click the “Customize” button for the File System Shield → click “Exclusions” → click “Add” and type in the full path for the files you want to exclude - > keep clicking “OK” to back out of the screens until you come to the main GUI.
If you know that they are FPs, you don’t say how you know or what the avast alert is.
You should submit the files to the avast virus lab as a FP, if confirmed then the signature can be corrected. This then helps all avast users who might also have this file.
If the file was in the chest you can right click on it in the chest and ‘Submit to virus lab…’ directly from the chest.
?? I tried this recently (maybe a week ago) - never got any answer.
You generally don’t get a reply unless they require more information.
They deal with it in the background and if confirmed as an FP the virus definitions get updated - your confirmation is essentially when you scan the file in the chest and it is no longer detected. You have to scan the copy in the chest as scanning the file outside of it ‘where you have added an exclusion’ won’t work.