"Which one should I buy is the biggest question we get," said Michael Flanagan of Michael and Son Services.
The more scrunched up the filter is, the more particles it can trap. When they're spread out, you can see the difference in surface area — and don't judge a filter by the wiring on the outside, it's merely a structural element.
Each home has different variables, but Michael has found that most houses have undersized ductwork. The filter you choose affects the efficiency of your system.
"Air flow is extremely important to heat pumps. If you restrict the airflow, you're going to shorten the life and raise your energy bills. A lot of people do that in an effort to clean their air."
This monometer reads how much air is being pulled through the system. The cheapest filter goes first.
"You see the air is just slightly pulling this in."
It's the best for moving air...
"Our negative pressure's gone up to .21."
...but it does the poorest job cleaning that air. Moving to the mid grade, the vacuum number goes up to .35. It's trapping the dirt, but restricting the airflow.
"And here's the expensive one. We're still at about the same number, even though it's typically considered a much more restrictive filter."
If you suffer from severe asthma, allergies or immune deficiencies, the most expensive filter may be a necessity... but for most people, the mid grade will get the job done.
"You can see this gauzy material here, that's going to hold more dirt, so I tend to think this filter will run a bit longer before loading up with dirt, where this one will not."
Michael advises changing filters every month only in the summer and the winter when the system is running more often.
But you could need to replace more frequently — based on pets, flooring or the location of the intake.