As a rule, a technician should perform a service of the HVAC system once a year, but the filters will need to be changed every 3 months depending on the level of use. These might require changing more often than that, maybe even once a month. You should consider changing the filters this often if you have pets or a large family. The reason is because of the extra dust, dirt and pet dander which circulates around the home. If a member of the household suffers with allergies or you smoke indoors, you should also change the filter every month. Remember that airborne particles outside will quickly find their way inside the home. This is something to consider especially if there is construction going on around your home, if there have been any wildfires in the area, or if you live in an area surrounded by a lot of agriculture as these may be reasons to change the filters more frequently as well.
If the filter becomes damaged or ends up becoming damp or wet for any reason, these are times when the filter should immediately be changed as they would stop the system working effectively and in the case of them becoming damp, mold could quickly develop and make indoor air quality a hazard.
As we can see, good home maintenance is essential to saving money on big repairs later on and also helps preserve a healthy environment in the home.