Dust, allergens and pollutants will not escape from the indoor air as the air passes through the filter and enters the vent and returns. Filters only work if air has to go through them. The filter has air resistance and a gap does not, so if you leave a gap of 1, a disproportionate amount of air will flow through the hole, which will further worsen the situation. Using an incorrectly sized air filter won't necessarily damage your HVAC system, at least not immediately.
However, it does have an impact. Using the wrong size reduces the efficiency of your heating and cooling system. This can add up quickly and become an apparent problem that you're likely to notice on your next utility bill. All air purifiers can remove pollen, dust and other allergens from an enclosed space where they are installed.
But for them to work properly, the air purifier must have a capacity and size that correspond to the size of the room. If you install an air purifier that is too small for your room, you will not be able to clean indoor air at the desired speed. With large rooms, you will need an air purifier that is capable of treating a larger volume of air per unit of time. That is, you will need a larger air purifier that has greater capacity and size to perform the job properly.
In short, yes, you can cut an air filter if you know what you're doing, and if the filters you're using don't get too weak from the cut. The filters of the oven must fit securely, but must not be forced into position. If you have to force the filter into its groove, it's probably too big. Forcing an incorrect filter size on a filter can cause it to bend, damage the filter, or reduce its ability to function properly.
Filters are smaller than their slot to allow easy replacement. Some HVAC units may require a filter with unique or unusual dimensions. In these cases, you need to order a custom filter. If an air filter is too small, air gaps will be created and contaminants will bypass the filter material.
Regardless of which type is best for your individual HVAC system, it is important that you change or clean your air filter regularly. When buying an air filter, it's important to note that the air filtration industry standard is to make the filters measure a little smaller than their slot or frame, so that they can easily slide into place without bending or breaking. AC filters are available in many different sizes, so it can be overwhelming if you're not sure what filter size you need. A purifier is also worth considering if your unit cannot handle a full HEPA filter, and someone in your household has the possibility of having respiratory problems. Most white pleated air filters are inherently the same within each efficiency level, varying slightly, if at all, between brands.
Note that the size shown in bold type on the filter frame is the nominal size of the filter, which is likely to differ from its actual size. While a good quality filter can do a lot for your HVAC system and your home, you should never underestimate the importance of HVAC maintenance. You may be able to buy a HEPA filter air conditioner for your home in a few years' time at a relatively cheap price. Choosing the right filter can extend the life of your air conditioner while ensuring that you and your family enjoy clean, clean air for years to come. If you are especially concerned about indoor air quality but don't want to go broke with a more technologically advanced purifier, an extended media filter should work fine without interfering with normal HVAC operation. Once you reach MERV ratings between 13 and 16, you'll be firmly in the range of medical-grade air filters.
It's a common misconception that using an air filter with a higher MERV (Minimum Efficiency Reporting Value) rating is always best.