Since air cleaners are located between the air return duct and the furnace or air conditioner, they filter all the air as it flows into the home's ductwork.
Adding a HEPA air cleaner to an HVAC system prevents the dirt and debris from building up inside the unit. This makes the system last longer. However they are expensive to purchase, costing about $400 to $800.
Costs vary greatly by region (and even by zip code). To get free estimates from local contractors, please indicate yours.