[dgacmu]

A deep merv-13 with a lot of pleats can have a very reasonable pressure drop - you just have to shop a little more carefully.

I would stick with merv-13 because you'll get solid performance across a lot of things you might want to remove, from viruses to general pm2.5 and things like volatilized cooking oil. Clean air is awesome and tire dust isn't the only thing that's annoying.

[ruralfam]

I agree completely re: mev-13 == optimal solution. But the word "pragmatic" hits me hard. Merv-13 when new/clean start out with pretty restrictive flow. They catch a lot of particles so restriction increases rapidly. At some point the CFM loss means the filter is much less optimal. All the studies I read used new filters, smoke-filled rooms, a day's treatment. It is obviously impractical and very, very expensive to replace a merv-13 filter every few days. There are no reusable merv-13 filters that I could find. If there is a study about merv-13 effectiveness over 30 days vs. merv-8 I would love to see it. I would love to use merv-13, but just cannot get my head around how it is a practical, affordable solution across years and years of use, and let's say a month between filter renewal. Let me know if you have good insights as I am pretty worn out researching this. Thx, RF

[Implicated]

I've been down this rabbit hole for a while now and sadly can't seem to find the article about the filtrete vs others, but there's been some people who tested the 'load' on these furnace filters and the Filtrete filters far exceeded everyone else in terms of airflow as the filters loaded up.

Re: Filter costs - stock up when costco has them on sale, which seems like every few months. They've got Filtrete 2500 (merv 14) for 3 filters for ~$35 if I remember correctly. I use them in my CR boxes and those I built for family (which I give them with a 3 pack of new filters and also instruct them to refill during costco sales)

I built one for a local stray cat rescue where it literally sits in the middle of the living space for 10+ cats, it's 4 months now since they started using it and the filters look quite dirty but the air flow is surprisingly still very good. (4x Noctua NF-F12 iPPC 3000 fans and 4x 16"x25"x1" Filtrete 2500 filters)

Here's some info re: which merv levels work best with various fan combinations (looks like if you're going to go with higher merv you'll need the static pressure to be able to continue to pull through them with any reasonable airflow once they're getting loaded up with stuff) - https://www.cleanairkits.com/blogs/news/what-happens-to-cadr...

[dgacmu]

I ran a corsi-rosenthal box 24/7 for a year during covid with 4 merv-13 filters and the airflow stayed pretty good. Depends of course - we don't have pets and were running the HVAC filter full time also so it was a pretty clean environment. I would bet that the lack of a pre-filter would kill things fast if you had pet hair or lots of dust. But I suspect 6 months is totally reasonable from a "provides effective filtration" perspective.

Remember that as the filter starts to get dirty, its filtration effectiveness actually increases, though the airflow rate drops. CADR will drop but less than just watching airflow would predict.