“It's a useful approach to monitor the pressure drop across the filter,” Li says. This is a good way to know when it's the right time to change the filter because otherwise it takes a lot of guesswork.” She says the typical three-month replacement recommendation is based on the assumption of 20% runtime of your HVAC system (about five hours a day). Much of this depends on your climate, but Li says a recent study found that the average HVAC runtime for 20 homes in a year in Toronto was 10%, meaning those people would likely replace their filters less often.
As for the ruling on MERV 13, Li said that higher flow resistance will cause HVAC fans to work harder. Depending on your system, the fan may be stop overwork, reducing airflow and potentially damaging the cooling coils. However, a higher MERV rating does not equate to higher flow resistance. It depends on the quality of the filter, as Li says she has seen MERV 13 filters have lower flow resistance than 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 are using a MERV 8 filter with no problems then I don't think there will be any trouble using a MERV 11, MERV 13 filter or even MERV 14 just because even if there is a difference in flow resistance it is relatively small,” she said. “I think most systems will be able to handle that, especially if you don't change the filter for a whole year.”
Those using older systems should be careful as they may not be able to handle the high efficiency filters. She suggests listening for sounds and feeling the flow coming from the cooling and heating vents in your home.
The good news is that Woosh's smart filters can detect problems with your HVAC system. The company says it can identify early signs of coil freeze-up, which if left untreated can cause irreparable damage. It manages this by checking pressure drop and flow rate along with temperature and humidity levels.
Thankfully, using the MERV 13 filter does not appear to have any adverse effects on my system, and I have not received any reports of problems with my HVAC. My only concern is that, according to the application, i still no need to change the filter even though it's been nine months since I installed it. My wallet is happy, but everything I've heard and read about the filter suggests I should have changed it by now.