Use the free Comodo below. And if u have AV already installed, just uncheck the AV installation in the Comodo. Its easy to configure it.
Download just the firewall, if that's all what u need.
U can use free Avast
along with free Malwarebytes
and Comodo Firewall
that is free, but got great results in defending your PC. And u can configure it to your satisfaction with ease.Avast! -- Free Antivirus Malwarebytes Anti-Malware -- helps you defeat Malware once and for all SUPERAntiSpyware -- Advanced Detection and Removal Comodo Internet Security -- The best free Firewall