When it comes to air filters for your home, the highest recommended MERV rating is 8.This is because filters for ventilation grilles and return vents are a great way to reduce indoor allergens, but they are not a long-term solution. As a rule of thumb, these filters should be replaced every month or two. If you have two large fiberboard air boxes in the attic, they will have large, flexible tubes that lead to the different return ventilation grilles. Before installing filters in the grilles, make sure to turn off the heating or air conditioning system and clean the vents and return vents of any dust or debris.
Some air conditioning systems have filters inside the return air ducts scattered throughout several rooms in the house. The air filter is usually placed in the return ventilation grille so that the air conditioning system can absorb clean air, free of particles and debris that could affect sensitive parts, such as the evaporator coils. However, after cleaning your ducts, you may notice thick dust on the very large duct located inside the air intake. In this case, you may want to install a large 19-inch x 20-inch x 5-inch grille and an air filter in the large return air chamber next to the air handler.
When it comes to selecting an air filter for your home, it's important to consider the MERV rating as well as alternative scales such as Home Depot's Air Filter Performance Rating System (FPR) or the MPR (on 3M Filtrete air filters). Central air systems are not designed to work with the pressure drop caused by several standard air filters. A cut-to-size filter comes in a roll of material that you can cut to fit the shape of the ventilation grille. It's also essential to have your air conditioner serviced regularly by an HVAC professional, check if the air ducts need to be cleaned, and identify any leaks in the ducts. This is because the return duct draws air from inside the house and circulates it to the air conditioning system for heating or cooling.
Unfortunately, this system acts as a vacuum and can suck up all types of hair, so you may need to clean your medical filter more often.