When we click on the heat and push warm air we can send insect parts air bourne that can cause us to react. Change the filter every three months but also have your whole system cleaned every three to five years. 2. HVAC Cleaning is often included as part of a mold remediation as the furnace/air handler is often housed in contaminated basement spaces and the return air vents may pull air from a contaminated area that can be recirculated to other areas of the home.