1. What does the air conditioner filter at the intake catch?
An air conditioner sucks in room air to cool or warm it. The filter at this intake is designed to catch fine particles in the air [1]. The dust in a room is called house dust. According to Panasonic’s explanation, house dust includes dead dust mites, their droppings, pollen, and mold. Some of this comes from outside, like pollen, while other parts are born inside the room and fly around, like dust mites and mold [3]. If you have ever taken out a filter, you may have seen a thin layer of dust on the mesh. That dust is part of what was mixed in the room’s air. But did the mesh stop every single particle that was in the air?
2. Why does fine dust pass through the filter and reach the heat exchanger?
Panasonic’s cleaning guide states that larger dust particles are stopped by the filter, but fine dust passes through the mesh and attaches to the heat exchanger [2]. The heat exchanger is a part deep inside the air conditioner that exchanges heat with the room air. When air blows through the mesh, larger dust stops, but fine dust travels with the wind. If the mesh cannot stop everything, is it useless? If large dust stops first, the amount of dust reaching the back decreases. It is easier to understand if you think of the filter as a first-stage net protecting the internal parts. However, the exact fineness of the mesh (in millimeters or mesh count) is not in official documents, so we cannot say exactly what size starts to pass through.
3. Why can dust and oil inside an air conditioner feed mold?
Panasonic’s guide notes that dust and oil attached to the heat exchanger can sometimes become a nutrient source for mold [2]. Because it says "can sometimes," it does not mean mold will definitely grow if dust attaches. Still, the value of reducing the dust that reaches the back becomes clear. You can remove and clean the filter while it is collecting dust. However, what sticks to the heat exchanger is not easy to remove in a typical home. The first-stage net has the role of stopping dust in an easy-to-clean place first. So, what happens to the air conditioner’s performance when that net becomes full of dust?
4. How much more electricity does a clogged air conditioner filter use?
A column by Tokyo Gas states that if the filter is clogged, efficiency drops, electricity costs rise, and odors may appear. The guideline for cleaning is at least once a month. If you use it every day during a season, it should be once every 2 weeks [1]. In a test by Mitsubishi Electric, assuming 8 hours of use per day, if the filter was not cleaned for about half a year, power consumption worsened by about 12% compared to a new filter. The manufacturer recommends cleaning once every 2 weeks [4]. In a Panasonic test (model CS-F401D2, annual power consumption), the unit with no filter cleaning used 1,814 kWh, while the unit with automatic cleaning used 1,544 kWh. The difference was 270 kWh [5]. This number includes the cooling period for the year, not just heating.
To compare these numbers on the same scale, if we take the automatic cleaning unit as the base, 270 divided by 1,544 is about 17.5%. If we take the no-cleaning unit as the base, 270 divided by 1,814 is about 14.9%. This looks different from Mitsubishi’s about 12%, but they are comparing different things. Mitsubishi measured the difference from a "new filter" over about half a year, while Panasonic compared the difference from "automatic cleaning" over a year’s total power consumption. Rather than one being wrong, it is safer to read them as separate numbers with different conditions. Both are tests of specific models and conditions, so the increase will not be the same in every home. However, both tests agree on the direction: not cleaning leads to higher power usage.
5. Do air conditioners with auto-clean still need filter maintenance?
Air conditioners with auto-clean functions use brushes to remove dust from the filter, storing it in a dust box or expelling it outside. The mechanism differs by manufacturer and model [6]. For example, a model described by Hitachi automatically cleans the fan, not the filter. It reverses the fan’s rotation to collect dust on the heat exchanger or drain tray, then processes it with freeze-washing [6]. The place where dust is removed and where it goes afterwards are different from the brush-style filter systems. Not all models work this way. Even on the same Hitachi page, it states that depending on usage and environment, the auto-clean function may not remove all dirt. It advises checking the dust box once a year as a guideline and cleaning it if dust has accumulated [6]. Automatic cleaning greatly reduces effort, but it does not reduce it to zero. This is based on one company’s explanation, so it does not mean other companies are the same. Automation reduces daily effort, but it does not replace human checks.
6. How can you check your own air conditioner filter by observing and calculating?
You can try one observation and one calculation with your home air conditioner filter. First, check the instruction manual for how to remove the filter. Stop the operation, then remove it with an adult. Working at high places is dangerous, so if you use a ladder, have someone support you. Once removed, hold it toward a bright window to observe the mesh and how the dust is attached. Can you see light through the mesh? Are there places where overlapping dust blocks the light? Compare this with the explanation in this article to observe where dust is attached. Next, use the numbers from the Panasonic test: 1,814 kWh and 1,544 kWh. Calculate 270 divided by 1,544 with a calculator. It should be about 0.175, or 17.5%. Then calculate 270 divided by 1,814 to verify that the percentage changes when you change the base. Finally, explain in your own words why this differs from Mitsubishi’s about 12%, based on the test conditions (time period and comparison target). If you want to read the original sources, they are listed in the "Sources" section. Mitsubishi’s "Teach Me! Kirigamine" includes test conditions, which is a clue for reading the numbers.
Observation: Check the removal method in the instruction manual, stop the operation, and remove the filter with an adult. Do not push yourself when working at high places.