Ask the internet how often to change an air filter and you will get "every 90 days." That number was written for a house with a lawn, a few rainy months and a heating season. In Tucson, where the air conditioner runs for most of the year and the air is full of fine dust for much of it, 90 days is often too long. Here is how to set a schedule that fits where you actually live.
Why the filter matters more than it seems
The filter is not mainly there to clean the air you breathe, although it does help. Its first job is to keep dust off the indoor coil and the blower. A coil coated in dust cannot absorb heat, a dirty blower wheel cannot move air, and the result is a system that runs longer, cools less and costs more. A badly clogged filter can starve the system of airflow entirely, freeze the coil into a block of ice and shut you down on the hottest day of the year. It is the cheapest part of the system and the one most likely to cause an expensive problem when it is neglected.
A starting schedule for Tucson
For a standard one-inch pleated filter:
- Every 30 days from June through September. The system is running nearly around the clock, and monsoon storms load the air with dust.
- Every 45 to 60 days the rest of the year.
- Every 30 days year-round if you have pets, if anyone in the house has allergies or asthma, or if the house is near an unpaved road or open desert.
For a thicker four- or five-inch media filter in a dedicated cabinet, the schedule stretches to roughly every six months, or sooner if it looks loaded. These filters hold far more dust before airflow suffers, which is one reason we like them for Tucson homes.
None of this is exact. The honest answer is to check the filter monthly during summer and change it when it looks grey. Hold it up to a light; if you cannot see through it, it is done.
Which filter to buy
Filters are rated by how fine a particle they catch. A higher rating catches more, but it also restricts more airflow, and many residential systems were not designed for the densest filters on the shelf. Putting a very high-rated one-inch filter into a system built for a basic one can cause the same airflow problems as a clogged filter, only from day one.
For most homes a mid-grade pleated filter is the right balance. If you want better filtration for allergies, the better route is usually a properly sized media cabinet rather than a denser one-inch filter. We can tell you what your system will tolerate during a maintenance visit.
Avoid the cheap fiberglass panels that you can see through. They protect the equipment from very little.
Make sure it is installed correctly
Two things go wrong constantly. The filter goes in backwards, against the airflow arrow printed on the frame, which lets it collapse and bypass. Or it is the wrong size for the slot and air simply goes around it. Match the size printed on the old filter exactly, and point the arrow toward the blower.
What a clogged filter costs
A restricted filter does not just make the house warmer. It raises the electric bill, because the system runs longer to do the same work. It shortens the life of the blower motor. And it is one of the leading causes of the frozen coils and compressor failures we see every summer, which are repairs that cost hundreds of times more than a filter.
Beyond the filter
Changing the filter is the one piece of maintenance every homeowner should do. It is not a substitute for a proper tune-up, which checks the parts a filter cannot protect: the capacitors, the refrigerant charge, the electrical connections and the outdoor coil. If it has been a year or more, schedule a maintenance visit or call (520) 261-3909, and set a reminder on your phone for the filter in the meantime.