The filters don't need to fit an “airtight” seal, but they should be easy to install and uninstall, and not so small as to move freely inside the unit. Custom-made air filters offer the same benefits as regular air filters, with an added bonus of being able to cut them to any size or shape you need. It should fit a little tight. A perfect fit means there's no turbulent air bouncing back.
The oven filters should fit properly, but there is no need to force them into place. If you have to force the filter into its slot, it's probably too big. Forcing an incorrect filter size on a filter can cause it to bend, damage it, or reduce its ability to function properly. The filters are slightly smaller than their slot for easy replacement.
Some HVAC units may need a filter with unique or unusual dimensions. In these cases, it is necessary to request a custom filter. 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 weaken too much from the cut. These gaps are normal and usually don't cause problems.
When the oven is operating, air pressure forces the filter against the face downstream of the slot, effectively sealing the opening. Unless you are concerned about respiratory conditions or are sensitive to poor air quality, you rarely need to exceed MERV 8.There are a number of great options for buying air filters online and having them comfortably delivered to your door. Do not stack several smaller air filters on top of each other to place them on a larger air controller. It's possible that, in a few years, you'll be able to buy an air conditioner with a HEPA filter for your home at a relatively low price. When you buy a filter online, the actual size appears at some point in the product vignette or in the product description.
If you can't find your size in the store or need a custom-made air filter, online retailers are probably the best option for you. Ultimately, the equipment you choose will determine how flexible your system is, how tight it is for your property, and if you need to cut your air filters first. Typically, you'll see filters with a MERV lower than 4 in residential ovens, window-mounted air conditioning units, or as a pre-filter in commercial units that need multiple filters. When deciding on an air filter for your HVAC system, there are a few different things to consider. HVAC service companies often offer air filter replacement services in addition to system repair and unit installation services.
Traditional flat panel air filters are the least expensive, but also the least effective. For common brands of HVAC systems such as Goodman, Lennox, Trane, Rheem York, Coleman and Carrier, most standard air filter sizes will work. While some air filters fit perfectly without requiring any modifications, this may not always be the case, especially if you have ducts that deviate from standard designs. In this case, you'll need to round down to the nearest whole number to determine the nominal size of the air filter. Conversely, if you are replacing the filter in a window air conditioner, you may want to make it a little smaller so that the filter fits in the unit without having to force it.