Brisk Box Kit

Build a [box fan air purifier](https://www.reddit.com/r/crboxes/comments/1hi3z6h/portable_box_fan_air_purifier_with_shroud/). It's just as effective as some commercial air purifiers that are at least 10 times more expensive. You can use the money you save to build more air purifiers. If you want a quiet air purifier, your best bet is a [Brisk Box Basic Kit](https://www.cleanairkits.com/products/brisk-box) from Clean Air Kits. Like a box fan air purifier, this uses furnace air filters instead of special proprietary filters.

Your first option should be a [box fan air purifier](https://www.reddit.com/r/crboxes/comments/1hi3z6h/portable_box_fan_air_purifier_with_shroud/). It's cheap, easy to build, and more portable and space efficient than the Corsi Rosenthal box based on the 20-inch box fan. Use a Lasko 20-inch box fan. For the filter, you can use a 4-inch-thick MERV 13 filter, a 1-inch-thick MERV 10 filter, or a 2-inch-thick MERV 11 filter. This box fan air purifier will be just as effective as some commercial air purifiers that are at least 10 times more expensive. You can use the money you save to build more air purifiers. If you want a quiet air purifier that doesn't get in the way of movies, TV shows, conversations, etc., your best bet is a [Brisk Box Basic Kit](https://www.cleanairkits.com/products/brisk-box) from Clean Air Kits. It's quiet because it uses PC fans. You save money in the long run due to the superior energy efficiency and because the furnace air filters are much more cost effective than special proprietary filters.

Jim Rosenthal (half of the duo behind the Corsi Rosenthal box) did an experiment comparing a Corsi Rosenthal box using MERV 11 filters against a high-end commercial air purifier using a HEPA filter. You might think that the MERV 11 filters (with lower filter efficiency than MERV 13 filters and MUCH lower filter efficiency than HEPA filters) would have been left in the dust (pun intended). In contrast, the cheaper and cruder Corsi Rosenthal box outperformed the commercial air purifier with the HEPA filter. In other words, the cheap and crude air purifier was MORE effective at cleaning the air than the expensive commercial air purifier.

Seconding air cleaners that use PC fans. The [AirFanta 3Pro](https://a.co/d/8LTLqZy) is great, but I admit a bit higher than the price point you mentioned. It moves and cleans the air quite efficiently even on the quieter speeds. I'd recommend buying from AirFanta/Adam Wong and avoiding the copycats. Clean Air Kits also has a [4-fan Brisk Box](https://www.cleanairkits.com/products/brisk-box) that does its job very quietly and consistently. I overlook the fact that it's more utilitarian than elegant, but I understand why that be a "no" for others. It has a small footprint too. One downside is that it's $104 for the kit, and the filters are an additional purchase which might not work for your budget. Plus side (at least for me) is that these filters are easy to get preordered to my local home improvement store.

if you ever feel like making your own air filter, check our r/crboxes for some inspiration. I have an coway airmega, a 6 fan cr box from NorthBox, a levoit mini, and one of the tiny ikea air filters. every room gets a different size and type of air filter according to the needs of that room.

Make your own "brisk box" from CleanAirKits. I do 12x12x1 boxes and I think I've gotten the price of the fan lid to about $80 DIY. 2 of those would be better than half the HEPAs in your budget. More so than just a filter, you should have a doffing process. E.g. Figure out your air volume, CADR (clean air delivery rate) and then you will have an ACH (air changes per hour). This lets you make informed decisions about how much filtration you buy and how safe that filtration makes you feel. I aim for 10-12 ACH and the recommendation I see most often is 12.

I bought the 4-fan Brisk Box Basic in January and while the price has jumped $30 since then It is incredibly quite and consumes 6-7 watts according to my Kasa Smart Plug. Unfortunately, I'm not sure about the air exchange rate since I'm currently using it in a larger space than it was intended for.