[runnerup]

I would personally get the silenced fans in the largest diameter you can afford / fits in your desired space because it will move larger amounts of air more quietly. The apartment was 700 sq. ft. I got the silenced 6" and it's reasonably quiet at most speeds, and not that loud at the highest speed -- putting filters at both intake and outlet greatly reduced the noise vs. just one side.

If you get the filters and fans in the same diameter they will just slip together without any additional hardware. But it will be quite wobbly. I used velcro (monoprice, laying around for wire-taming) to secure it to a vertical bookshelf.

My BOM: - $199: TerraBloom 6" Silenced EC Inline Duct Fan, ECMF-150-S, 288 CFM, 36W

- $114: TERRABLOOM 6" AIR FILTER 24" LONG, 1.8" (46MM) THICK,

- $80: TERRABLOOM 6" AIR FILTER 16" LONG, 1.8" (46MM) THICK

I'd probably go 8" if I was buying today, I hedged a bit cheaper because I wasn't sure if the quality/performance would be what I needed. This has been running for 9 months now with almost no noticeable degradation in performance, although I'm not currently quantifying it. Eventually I intend to install 3 VOC sensors, one outside the unit near the intake, one inside the unit, and one outside the unit at the outlet....to measure the VOC scrubbing efficiency curve over time and assist in deciding when to replace the carbon.

We've been running it 24 hours per day, usually about 40% but sometimes at the lowest setting (maybe 25%) and sometimes at the highest 100% setting.

After 9 months, it can still use it for point sources of concentrated smells like soldering and it captures 100% of the odors. And this is operating in a high-VOC environment near a lot (dozens) of chemical plants on our side of the city.

[birken]

I've been running a similar setup next to my litter box for about 2 years using "Vivosun" products, which seem like a cheaper knockoff version of Terrabloom.

The Terrabloom stuff looks higher quality and I can't compare it directly to Vivosun, but I've got no complaints about my Vivosun duct fan or carbon filters. I'm not necessarily suggesting one brand over the other, but just to add that you can run a knockoff version of this setup for a lower cost.

[ornornor]

I’m trying to picture the systems. They’re basically a carbon filter sandwiched by two fans, it runs the air through the filter and puts it back in the room? Or is it connected to a vent that exhausts the air outside (or does it filter one coming outside air?)

[runnerup]

In my case, a fan sandwiched by two filters. Recirculates through room so filtration will follow the differential equation models for “CSTR’s”, which are Constantly Stirred Tank Reactors.

[TheBlerch]

Which Vivosun products do you use and how large is your space? Is there a HEPA filter in the system, or only carbon?

[lend000]

Love coming to HN and learning from the in-depth research of others on topics like these.

How important do you think the external fan is? (versus just placing it next to the modest airflow of a HEPA filter, as a sibling commenter suggested)

[runnerup]

Very important. “Non-ducted” suction doesn’t have enough static pressure to pull air through a carbon filter, will pull the air around it instead. In electrical terms, this would be like feeding a power sink with a large gauge copper wire and a medium resistance resistor in parallel. 0.01% of the electricity will pull through the resistor, 99.9% will come through the bare copper wire.