When it comes to air filters, size matters. The filter has air resistance and a gap does not, so if you leave a space of 1, a disproportionate amount of air will flow through the hole, making the situation even worse. A larger filter contains more dust, and a typical 20x25x1 filter has almost 30% more surface area than a 16x25x1 filter and therefore has 30% more dust holding capacity. In reality, you cannot change the size of the filter, since it must fit the grill that was installed with your oven.
However, you should keep this in mind when deciding on a filter program. Using an improperly sized air filter won't necessarily damage the air conditioning system, at least not immediately. But it will have an impact - using the wrong size reduces the efficiency of your heating and cooling system. This can add up quickly and become a more obvious problem that you're likely to notice on your next utility bill.
If you have questions about your boiler, call our HVAC team. We'll make sure you're using the right size air filter for your air conditioning system. My sister can get fairly cheap 3M oven filters, but the size that my oven has installed right now is 20 x 25 x 2 inches, and the only ones I can get are 20 x 25 x 1 inch. You can get a 1-inch cheap one and a 1-inch face and put your face one second later than the cheap one in the airflow.
The cheaper one will serve as a pre-filter that filters large things, such as cats or hair. However, two good filters can block air flow enough to cause problems, so if you use two filters together, make sure one is cheaper than the other. Honestly, you just need to put in a filter, with a little bit of adhesive tape to keep it in place. Don't do this - two filters have twice the surface area of 1 filter and the filter material itself is the same thickness.
You can only use one filter of 1, but it will clog twice as fast. Frugal isn't spending a dime chasing pennies - so if you want to save money on your heating and cooling bills, make sure you're using the right size air filter for your system. If you have any questions about your boiler or need help finding the right size filter for your system, don't hesitate to call our HVAC team.