Generation 1, 2012 till present. Inspired by dust and the fact that we would leave a fan on to drown out road noise, dogs running through the house. It's pretty much just dust control. Useless for most pollens, totally useless for smoke and viruses. Great for if your house has pets and/or people living in your house or if you have any kind of dust. It's just a cheap 20x20 air filter taped to a 20 inch box fan. Tools: tape, a filter and a fan. Difficulty level: total retard. If you can open a box and tape 2 things together you can do this.
Generation 2, 2018-2021. Inspired by the window lickers running the state if California, who's failed environmental policies caused the entire state to burn from one end to the other and their smoke coming here. It's any size air filter you want duct taped to a same size peice of cardboard with a bathroom fan sized hole duct taped to the other side, add spacers and tape. Good for smoke, viruses, pollen. The most difficult part is knowing that a box fan can't pull hardly any air through a number 13 or higher filter. Cheap bathroom fans are noisy as hell, the one I used is a premium quiet $70 in 2018 dollars, bathroom fan. Difficulty: if you can use a box cutter with out having to go to the emergency room you can do this. Partial reconstruction. Spacers so the filter doesn't just vacuum it's self against the cardboard. Where the bathroom fan was duct taped. This was supposed to be a 3 to 6 month test that lasted nearly 2 years. You can see where the filter was taped to the cardboard. It worked great.
Generation 3, 2021 and up. Inspired by generation 2 and the window lickers in California only managing to burn more of their state than the previous year. I figure if more of California is going to burn more, every year till the fires run out of shit to burn I better go big. The single filter, single standard flow fan definitely worked, filter fan 3 will have that fan plus another one that moves twice the air as generation 2. Still under construction. It's about 80% complete. It's a divided, dual filter setup, dual fan setup. It's made with 2 premium bathroom fans, the standard flow 3 inch fan from generation 2 and my 4 inch high volume fireplace woodstove fan, which is also a bathroom fan. The high volume premium bathroom fan was $130 in 2017. Pictures are upside-down. The plywood is 3/4 inch premium birch plywood leftover from a 2017 project, I want to say this was like an $80 sheet of plywood 4 years ago, I'm sure it's over $100 a sheet now if you can find it. I went with 24x24 filters they are big, 24x24 is easy to remember, the 24x24 filter is only slightly more expensive than filters half to 2/3 that size. There will be a high end number 13 filter on one side and an ultimate number 16 filter on the other side. Both sides will have a cheap trash filter to stop the big dust and protect the super filters. Difficulty level: can you make a cabinet that doesn't look like total shit and wire some stuff up? The main disadvantage is to build this in 2021 it would probably be well over a $300 build in just materials. It's about 3/4 of a sheet of plywood so it's heavy, like a peice of furniture. You can make them any size or shape you want. Give it a going over with the sander, some stain and some polyurethane. A single smaller filter could be stashed behind a couch or under a table and be out of the way. I went big. I was going for over kill.
I have seen people using fan #1, box fan and filter in public places. It seems collect some particles but people that assume it collects virus germs are mistaken. This is a good reminder @oil pan 4. Our house has been so smoky and not having air conditioning, our eyes and throats are irritated. I think I will set one of these up today. I have fans and extra filters.
Bathroom fans are the cheapest most commonly available fans I know of that can develop enough pressure differential and still maintain good flow to pull air through one of those number 16 air filters that will catch smoke. Generation 1 will catch virus and smoke, maybe some where between 0.1% and 1% per pass, so effective, no. The viruses would become non functional due to environmental exposure before the Gen 1 fan could catch most of them. A bathroom fan pulling through a number 16 filter catches all the smoke and viruses, the only stuff that gets through is edge and seem leaks.
Something to ponder if Merv 13-16 becomes unavailable Bulk BFE95 Face Mask Air Filtration Media Material -Roll 42
If you have lots of smoke like we do, switch to a water filter system, they are super easy to make, and maintain, and will catch EVERY thing that comes along! Take a cheap 5 gallon bucket and lid, cut two holes in the lid, add a small high powered fan with an elbow and pipe to one side and a short pipe and elbo to the other. The intake pipe must be submerged below the surface of the water for this to work, and the outlet will be above the water level with the fan on the suction side! Stick the intake out the window and let it do it's thing! A much larger version can be made easy enough once you know how it works, and you can even set it up with a toilet level to automatically regulate the water level inside the system! Never change a filter again, just drain when it gets black and nasty, add a few drops of bleach to the fresh and your good to go!
Well filter fan generation 3 has been going for about 3 weeks. No California smoke yet but we are at the mercy of the winds. Both bathroom fans move a lot of air, hundreds of cfm, probably because there's no ducting to slow the air flow and the 24x24 filter offers almost no resistance to air flow. Oh and somehow this 3/4 inch poplar plywood is still only $60 a sheet at lows. I'm pretty sure that's what I paid for it in 2017.
I'll remember this the next time Kate Brown decides the best way to fight forest fires is to blame Republicans.
Filter fan gen3 is still going strong. I let the filters get really dirty before changing them and that only slightly reduces air flow. Have had some smoke from the fires burning in new Mexico.
I finally bought a 2.5 micron particle counter or pm2.5 counter. The gen3 filter fan keeps the pm2.5 reading 6 to 8 particles per liter of air. That's apparently really good. IDFK if it is or not. This phone takes shitty pics. They're all blurry unless they're wide angle from at least 6 feet.
Add another with the intake outdoors to pressurize the house. I use a small direct drive blower from a tv transmitter that pulls through a MERV 8 pleated 24x24 pre-filter and a 24x24 carbon pleated filter. Inside is a 20x20 sheet metal box with a blue micronite filter media pre-filter and another charcoal filter with a salvaged 20x20x5 HEPA filter from a clean room, with four 4" computer style fans. It only moves around 10 cfm. Attached to the HVAC system is an Aprilaire Energy Recovery Ventilator. This thing is awesome when the outdoor air is decent, you can smell the rain during a thunderstorm. When conditions are crappy the ERV gets turned off and the home built system turned on. Good post OP4. People overlook indoor air quality.
