Placing an air purifier about three feet above the ground can help capture air that flows both vertically and horizontally. However, any wall, furniture, or other object near the unit can interfere with this air flow, reducing the rate at which it absorbs and cleans it. Some air conditioning specialists have also found that thicker filters are better at providing a perfect fit that prevents unfiltered air from passing through. At the same time, a thicker filter is less restrictive and will allow better flow of purified air.
A 4 to 5 inch air filter is usually the best choice for those who need superior filtration. But there are situations where a thin filter is more suitable. For instance, if you sleep with the air purifier at a low temperature, make sure that the low-setting CADR is sufficient for the size of your room. Additionally, if you have an old 4-cylinder engine with a carburetor in which it is difficult to place an air filter due to area limitations, the shape and size of the filter element will determine its ability to flow maximum air to the engine. Tests of the K&N have shown that, in most two- and four-cylinder carburettors, air flow is greater when the diameter of the air filter is large compared to its height.
For maximum airflow, it is recommended to use the largest air filter element or assembly that fits the confines of the engine or engine compartment. Combining a thin air filter with a high MERV rate can also restrict airflow to the point of hampering efficiency and causing excessive wear. When it comes to placement, finding an air purifier with enough power (CADR) for the size of your room is more important than its position. But it's also important to keep the inlet at least 15 cm from any wall, furniture, or other object near the unit. This will help ensure that air flows both vertically and horizontally. The only exception to this rule is when a filter element is attached to a long slide, as is the case with cold air intakes on EFI engines.
If you try to use a 4-inch-thick air filter in a system designed for a 1-inch-thick filter, efficiency will actually worsen. But if your oven's air filter compartment is only 3 inches thick, then a 1-inch oven filter is better than a 4-inch filter; however, a 3-inch thick air filter is still your best option. In conclusion, finding an optimal height for an air filter depends on several factors such as size of your room, type of engine or oven you have, and type of filter you're using. The 4-inch thick air filter has a definite advantage over thinner filters in terms of longevity, airflow, and maximum filtering potential. But if space is limited or you're using an EFI engine with a long slide attached to its filter element, then you may need to adjust accordingly.
