This might seem like a small detail, but cutting an air filter down to a smaller size can sometimes damage the structural integrity of the filter. This is especially true for higher-end filters. The filter size should be listed in the instructional manual that came with your HVAC unit.
You can totally cut it to size. Just make sure you don't cut into the actual filter media because that's the part doing all the hard work. Folding might block airflow and make your HVAC work harder, not cooler. I had a buddy who did the same thing, and a quick trim did the trick.
If you suspect you've been using the wrong size air filter, take the following steps to minimize any potential damage: Replace the filter immediately: Swap out the incorrect filter with the right size to ensure optimal airflow and filtration.
If an air filter is too big for the slot in your HVAC system, it won't fit properly and may allow unfiltered air to bypass the filter. This can let in dust, allergens, and other particles, reducing indoor air quality. You may also damage an oversized filter when installing it.
Standard air filters have pre-defined nominal sizes for compatibility with most HVAC systems. Custom-made filters fit non-standard dimensions. The Nominal filter size for a custom filter may still round to convenient measurements, but its actual size matches the dimensions of the HVAC system or filter slot.
Using the wrong size filter reduces efficiency, air quality, and can even damage your HVAC system.
A filter that's too small will leave space where debris and particles can enter; a filter that's too large won't fit in the slot. You can't trim it down, either, since that will create gaps that allow things like dust, dander, pollen, and indoor air contaminants to enter.
Some air filters can lose their structural integrity and effectiveness if cut, especially if the person cutting it is inexperienced with air filters. Air filters that are cut improperly, or filters that will not withstand the structural change, can lead to improper performance and damage to the HVAC system.
One common problem with a poorly fitted air filter is that it can reduce airflow through the AC. This means the HVAC system requires more energy to push air through the filter. This will lead to an increase in electricity consumption. Air filters typically have instructions for how they should be installed.
Going down in thickness by an inch shouldn't be a big deal - for example, you should be able to use a 4-inch filter instead of a 5-inch filter. If you are considering a thicker air filter in order to improve air quality it may be better to focus on the MERV rating.
How Tightly Should My Air Filter Fit? If you have to bend, force, or jam your air filter into place: your filter is too big. On the other hand, if your filter does not come within 1-2 fingers' width of all four corners of your air system handler's slot or frame: your filter is too small.
The most common problem you will face with a backwards facing filter is simple inefficiency. If your furnace is forced to blow air through the non-porous end of a filter, it will take more energy to do so. The blower will be overworked and you will pay more money for your heating.
If the filter is too small, it won't cover the entire space and may allow dust and dirt to flow past. If you're not sure what size filter you need, check the manufacturer's specifications or ask your HVAC technician for help choosing the right product.
If the air filter is too large, it will cause the system to run slowly and reduce the efficiency of the filtration process. This requires more energy to run during the day and will increase your bills.
You can run the furnace without installing a filter, but only temporarily (such as overnight, awaiting a new filter). If you let it run very long without filtration, contaminants will build up.
The direction of airflow in the HVAC system can cause some confusion, and for good reason too! To ensure your furnace filter is put in the correct way, make sure the arrow on the furnace filter is pointing towards the furnace.
Do You Need an Exact Size Air Filter? Yes, you need the exact size air filter.
As a general rule, it is never a good idea to run your air conditioner or HVAC system without an air filter in place. Any amount of time spent doing so can lead to permanent damage and the possibility of needing expensive repairs.
Expensive air filters are made from higher-quality materials, last longer, are more efficient at trapping particles, and have a larger surface area to filter. This can lead to better indoor air quality and improved health.
The filters don't need to fit with an "air tight" seal, but you should be able to easily install and uninstall your filter without a struggle, plus the filter shouldn't be so small that it moves freely within your unit.
A low cut filter (aka high pass filter) reduces lower frequencies in your audio signal by a set amount. This means that it lowers the volume of your audio signal below a certain frequency. This can be a useful tool to remove unwanted frequencies from your audio signal.
Furnace filters are sized by thickness (depth), height, and length. The most common thickness is 1”, with 4” also being a popular choice for larger systems. Height and length combinations range from 10”x10” all the way to 30”x 30”. The most common sizes are 14”x 25”, 16”x 20”, 16”x 25”, 20”x 25”, and 25”x 25”.
If you keep experiencing this situation in your home, we recommend you start with a whole-house duct cleaning to eliminate most of the excess dust and dirt in your home's HVAC system. Then, consult with one of our expert heating and cooling technicians to find the optimal filter for your HVAC system.