I use both , i use only the firewall portion of comodo, but now i have turned on the HIPS
is there any conflicts between avast and comodo while using HIPS or is there any important rules to add to it?
Search the forum … plenty of avast/comodo posts in here
I have not encountered any problems; However, I got just one autosandbox active. Choose just one.
Just my experience using comodo with defense + and avast!, comodo has always recognized avast as a trusted program. Also have never set any exclusions in avast either. I don’t use the autosandbox. Hope this helps. 
I use avast and CFW v5.12 w/D+ with no issues. I do not use the CFW sandbox/kiosk.
There are quite a few members that use both. You shouldn’t have any problems.
Just do not install the Comodo anti-virus else you could see conflicts.