“It’s a helpful approach to monitor the pressure drop across the filter—this is a good way to know when it’s the right time to change the filter because otherwise, there is a lot of guessing work,” Li says. She says the typical three-month replacement recommendation is based on the assumption of a 20 percent runtime of your HVAC system (about five hours a day). Much of this depends on your climate, but Li says a recent study found the median HVAC runtime of 20 homes over a year in Toronto was 10 percent, meaning those folks would be able to replace their filters less often.
As for the verdict on the MERV 13, Li says that a higher flow resistance will make the HVAC fan work harder. Depending on your system, the fan could stop working as hard, decreasing airflow and potentially damaging the cooling coils. However, a higher MERV rating does not equal a higher flow resistance. It depends on the filter quality, as Li says she has seen MERV 13 filters with lower flow resistance than a MERV 8. Ultimately, Li says the main factor is the age of your HVAC system.
“If this is a relatively new system in good condition, and you have been using MERV 8 filters with no problem, then I don’t think there will be any trouble using MERV 11, MERV 13, or even MERV 14 filters just because even if there is a difference in the flow resistance, it’s relatively small,” she says. “I think most systems will be able to handle that, especially if you don’t change your filter for the entire year.”
Folks with older systems should be careful, as they may not be able to handle high-efficiency filters at all. She suggests listening to the sound and feeling the flow coming from the cooling and heating vents in your home.
The good news is that Woosh’s smart filter can detect problems with your HVAC system. The company says it can identify early signs of coil freezing, which if left unaddressed can cause irreparable damage. It manages this by checking pressure drop and flow rate along with the temperature and humidity levels.
Thankfully, using a MERV 13 filter doesn’t seem to cause any adverse effects on my system and I haven’t received any notifications about problems with my HVAC. My only concern is that, according to the app, I still don’t need to change my filter even though it’s been nine months since I installed it. My wallet is happy, but everything I’ve heard and read about filters suggests I should have changed it by now.