The EPA and NADCA recommend every 3–5 years for most homes. You may need it sooner if you have pets, allergies, recent renovations, or visible dust coming from vents.
At least once a year for a typical household. If you do heavy laundry or have a long vent run, consider every 6 months. A clogged dryer vent is one of the leading causes of house fires.
The National Fire Protection Association recommends an inspection and cleaning at least once a year, regardless of how much you use your fireplace.