When it's time to replace your air filter, the easiest way to determine what size you need is to look at what it says on your current filter. Air filters usually have their dimensions printed somewhere along the sides. Dimensions will include height, width, and depth. In some cases, air filter measurements are not necessarily indicated as exact physical dimensions.
Sometimes, the manufacturer uses a model number instead. If you have the model number, you can find out the dimensions. If your air conditioning system uses a whole-house filter (they are near the central furnace or air conditioning unit), the model number will most likely appear, not the dimensions. If your air conditioning system has an air filter, you can look up its size to make sure you can replace the correct filter.
Most filters have their measurements indicated on the side of the print, including length, width and depth in inches. They are usually displayed in that order. On the other hand, if the filter is too large, its frame will wrinkle, airflow will be restricted and longevity will be compromised. These filters are typically installed in wall-mounted return air vents (most common in the south) or in the air handler (more common in Mid-Atlantic and Northern states, where the air handler is usually placed in the basement near the oven).
For example, the filter label may have a size of 20 x 30 x 1, but if you measure it, you'll see that the actual size is smaller than the nominal air filter size of 20 x 30 x 1.If the filter is too small, it will be loose and some of the air (and dirt) will not pass through it. If your air conditioning system uses a thicker filter (usually between 4 and 5 inches and usually mounted on the air handler), it's likely to be specifically designed for medium-efficiency MERV filtration. If that doesn't work, you may be able to find out the proper dimensions of your air filter in your HVAC manual. MERV stands for Minimum Efficiency Reporting Value and is a measure of how effectively a filter removes particles from the air.
This means that if the air filter is not properly sized and sealed, all air and pollution will be completely dispersed and prevented from being completely filtered out. We believe that manufacturers' concerns are too cautious, in part because a recent innovation in air filters makes it possible to obtain high MERV ratings (11 to 1) with a low pressure drop. But those are rare circumstances and whether or not to pay more for a better filter depends mainly on whether or not cleaner air is a priority for you.
