Is an air purifier or an air filter on my HVAC system better for pet allergies?

Both help, but a standalone HEPA purifier is more effective for targeted allergy relief. HVAC filters only work when the system is running and typically use MERV rated filters that capture fewer small particles than true HEPA. A portable HEPA purifier runs continuously in the room where you spend the most time, providing constant filtration right where you need it.