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“It’s a useful approach to monitor the pressure drop across the filter; it’s a good way to know when it’s the right time to change the filter because otherwise there’s a lot of guesswork,” Li says. She says the typical recommendation for replacement every three months is based on the assumption of a 20 percent run time of your HVAC system (about five hours a day). Much of this depends on the weather, but Li says a recent study found that the average HVAC runtime of 20 homes over a year in Toronto was 10 percent, meaning those people could replace their filters less frequently.
As for the verdict on MERV 13, Li says that higher flow resistance will make the HVAC fan work harder. Depending on your system, the fan may arrest working so hard, decreasing airflow and potentially damaging the cooling coils. However, a higher MERV rating does not equate to greater flow resistance. It depends on the quality of the filter, as Li says he’s seen MERV 13 filters with lower flow resistance than a MERV 8. Ultimately, Li says the biggest 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 without problems, then I don’t think there will be any problem using MERV 11, MERV 13 or even MERV 14 filters just because even if there is a difference in resistance to the flow, it is relatively small,” he says. “I think most systems will be able to handle that, especially if you don’t change the filter all year.”
People 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 your home’s heating and vents.
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 not addressed can cause irreparable damage. It manages this by checking pressure drop and flow rate along with temperature and humidity levels.
Fortunately, using a MERV 13 filter does not seem to cause any adverse effects on my system and I have not received any notifications about problems with my HVAC. My only concern is that depending on the application, it doesn’t still I 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 the filters suggests I should have changed them by now.
