old4 Filter Build – A Corsi/Rosenthal Box also called the Compretto Cube. Top is a fan, but the bottom is just cardboard – no bottom filter.

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There are several different builds below. No matter which one you choose make sure you put a shroud on the front of the fan to enhance efficiency.

Here is a 4 filter build known as the Compretto Cube: hosted by Philip Neustrom.  This diagram is just a sample – very well-done build site!

Here’s another 4 filter build from Don Blair, citizen scientist in the Boston area.  Great Work Don!  Great NPR article on this.

PNG of this poster.

Very handy PDF download here.

Here’s a video on how to do it from This Old House:

Here’s another video build:

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