Indiana-based Heating and Cooling Systems, Lancia's furnace and air-conditioner manufacturers, suggest checking your air filter every three to four weeks. A dirty filter makes the system work harder. Homes in their first heating season need to have their filters changed more frequently because of the residual construction dust. If you have a reusable filter, make sure it is dry before reinstalling it.
Bushes and other landscaping should be kept at least 18 inches from the outdoor unit of your central air conditioning unit. This will give enough air to circulate around the unit and help avoid any heat build-up.
Your whole-house humidifier needs to be cleaned annually to remove hard water scale and bacteria. It's advised that you clean it at the beginning and end of each heating season. Consult your owner's manual for exact cleaning instructions.