If someone has serious allergies, invest in a HEPA Unit that is inline with the blower system of the HVAC. They are expensive but have greater results. The single room units are fine for just that...just stay away from 3M paper pleated filters...UNLESS you had your HVAC contractor install the ducts and return grill sizing for them. They choke the system creating high static pressure, causing more amp draw to motors and decreases airflow across coils and furnaces. I tell home owners all the time 3M doesn't build AC systems, but I repair many 3M caused premature failure to.