How often to change HVAC air filter, judged by sight

How often to change an HVAC air filter

How often to change an HVAC air filter depends on what the filter looks like, not on a date you set once and forget. Pull it out, hold it up to a light, and replace it when you can't see light through the pleats or a gray mat covers the surface.

The same filter serves the furnace in winter and the AC in summer. So the same look works in both seasons.

Read more about the cooling side in AC repair in Spanish Fork.

How can you tell a filter is dirty by sight?

A clean filter looks white or light blue, and you can see the pleats clearly. A dirty one turns gray or brown, and the dust forms a fuzzy layer on the side facing the return air.

Here is a simple way to judge it:

• Hold the filter up to a window or a flashlight.
• If light passes through the pleats evenly, it is still working.
• If whole patches stay dark, or you see lint and hair caught on the surface, replace it.
• If the frame bows or the filter feels damp, replace it as well.

Make the look part of your routine. Check it when you change a smoke alarm battery or when the seasons switch, and write the date on the frame in pencil so you can see how long that filter lasted in your house.

What shortens the life of a filter?

Some homes load a filter much more heavily than others. A filter that stays clean in a quiet home may turn gray after a busy stretch in another.

Common causes include:

• Pets that shed, especially long-haired ones
• Construction or remodeling dust
• Carpet and rugs that hold fine lint
• Open windows on dusty or smoky days
• A system that runs for long stretches

If any of these fit your house, look at the filter more often. Your own eyes are a better guide than a generic schedule. After a dusty project, check it when the work ends.

Why does the filter matter in both seasons?

The same blower pushes air through the filter whether the house is being heated or cooled. A thick layer of dust makes the blower work against a blocked path in either season.

The NOAA weather station near Spanish Fork averages 5,415 heating degree days and 1,013 cooling degree days a year. Degree days add up how much heating or cooling a climate calls for. Those totals show a year with both a heating season and a cooling season, so the filter is in use in both.

Where a furnace or an AC works hard in a season, a clogged filter makes the strain show. That is a reason to look before the first cold snap and before the first hot spell.

What are the signs of a clogged filter?

A blocked filter limits airflow, and low airflow causes several symptoms that look like bigger problems:

• Weak air from the vents, even when the system is running
• Rooms that stay warm in summer or cool in winter
• A system that runs for long stretches without reaching the set temperature
• A furnace that shuts off by itself before the house warms up
• Dust building up around the vents

Starved airflow can also let ice form on the refrigerant lines, because the indoor coil gets too cold. If you see ice or water at the indoor unit, read the guide on ice on the AC lines and water at the indoor unit and switch the system off first.

A system that starts and stops in short bursts is another hint. The guide on AC short cycling covers that pattern and its other causes.

How do you change the filter safely?

Changing a filter is a homeowner job. Follow these steps:

1. Turn the thermostat to off so the blower is not running.
2. Open the filter door or the return grille.
3. Slide the old filter out and note the size printed on its frame.
4. Check the arrow on the frame, which shows the direction of airflow. It should point toward the blower.
5. Slide in the new filter, close the door, and turn the thermostat back on.

If you smell gas while you are at the furnace, treat it as a safety matter. If you smell gas, leave the house, then call the gas utility from outside. If a carbon monoxide alarm sounds, get everyone out and call emergency services.

Anything beyond the filter belongs to a licensed contractor. That covers the cooling gas in the lines, wiring and other electrical parts, the furnace burner and gas valve, and any sealed part. A fresh filter will not fix those, and opening them is not safe.

What to do when a clean filter does not help

If you have changed the filter and the symptoms stay, rule out the other simple items: the thermostat and its batteries, the space around the outdoor unit, and whether the vents and returns are open. Then it is time to look at the equipment itself.

Where a contractor is available, the line connects the call to a licensed, insured contractor. Anything behind a panel is that contractor's work. We connect you with a licensed, insured HVAC contractor. The contractor confirms availability and fees.

For the full picture on cooling trouble, return to AC repair in Spanish Fork.