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A Corsi-Rosenthal Cube. This cube was constructed with 4 MERV-13 filters and features a cardboard bottom.

The Corsi-Rosenthal Cube (sometimes called a Comparetto Cube) is an inexpensive, do-it-yourself air cleaner that can be easily constructed out of a box fan and MERV furnace filters. The Corsi-Rosenthal Cube can give whole-room air cleaning performance comparable to commercial HEPA air cleaners that are 10x or more the cost. Total cost is around $100.

Construction guide

What's needed:

A visual guide to constructing a Corsi-Rosenthal cube with a box fan and MERV filters. This design will have the fan pointing to the side rather than up. Photo CC-BY al.hu.
  • 4 or 5 MERV-13 furnace filters. You will want to purchase 20" sized MERV-13 filters. For the 3M Filtrete brand of furnace filters, this is "FPR 1900." If MERV-13 is not available, MERV-11 filters can be used but performance will not be as great.
  • A 20" box fan
  • Duct tape
  • Some cardboard

How to construct - 4 filter version:

  1. Duct tape the filters together, forming an incomplete cube. Don't tape over the filter media part of each filter. 
  2. When taping the filters together, make sure to arrange each filter so that the air intake direction of the filter goes inward. The filters should indicate which direction the air is supposed to flow. So you want each filter's airflow direction to point into the cube, not out.
  3. There should be two empty sides of your incomplete cube. The box fan will go on one of these empty sides and the cardboard will go on the other.
  4. Cut your piece of cardboard to fit over the bottom area of the cube, where the cube will sit against the ground. Duct tape it to the bottom.
  5. Duct tape the box fan to the top of the cube. You can also choose to have the fan point outward rather than directly up into the air. The illustration below shows the fan pointing outward. Having the fan point directly up into the air is a bit better because it's less obtrusive.

Variations

5-filter version

Rather than placing a piece of cardboard on the bottom side of the cube, another filter can be added in place of the cardboard.  In this case, you would want to raise the cube off the ground (without blocking the entire bottom filter) so that the bottom filter could be utilized.  This would in theory lead to even less resistance on each of the filters, potentially prolonging the life of the cube or increasing the air output.

Two filter "wedge" design. 

A variation of the air cleaner can be made using two MERV filters (add details). This version is slightly less expensive (2 less filters are needed) and has a slightly smaller footprint.

History

As discussed in his original blog post, the design for the Corsi-Rosenthal Cube was detailed by Jim Rosenthal, CEO of Tex-Air Filters, and was dedicated to Dr. Richard Corsi. Neil Comparetto also detailed a similar design in a popular YouTube video, which he called a "Comparetto Cube."

See also

News / media stories

A Corsi-Rosenthal Cube. This cube was constructed with 4 MERV-13 filters and features a cardboard bottom.

The Corsi-Rosenthal Cube (sometimes called a Comparetto Cube) is an inexpensive, do-it-yourself air cleaner that can be easily constructed out of a box fan and MERV furnace filters. The Corsi-Rosenthal Cube can give whole-room air cleaning performance comparable to commercial HEPA air cleaners that are 10x or more the cost. Total cost is around $100.

Construction guide

What's needed:

A visual guide to constructing a Corsi-Rosenthal cube with a box fan and MERV filters. This design will have the fan pointing to the side rather than up. Photo CC-BY al.hu.
  • 4 or 5 MERV-13 furnace filters. You will want to purchase 20" sized MERV-13 filters. For the 3M Filtrete brand of furnace filters, this is "FPR 1900." If MERV-13 is not available, MERV-11 filters can be used but performance will not be as great. Important note: see the notes on MERV-13 filter tests below for brands to potentially avoid.
  • A 20" box fan
  • Duct tape
  • Some cardboard

How to construct - 4 filter version:

  1. Duct tape the filters together, forming an incomplete cube. Try to avoid taping over the filter media part of each filter. 
  2. When taping the filters together, make sure to arrange each filter so that the air intake direction of the filter goes inward. The filters should indicate which direction the air is supposed to flow. So you want each filter's airflow direction to point into the cube, not out.
  3. There should be two empty sides of your incomplete cube. The box fan will go on one of these empty sides and the cardboard will go on the other.
  4. Cut your piece of cardboard to fit over the bottom area of the cube, where the cube will sit against the ground. Duct tape it to the bottom.
  5. Duct tape the box fan to the top of the cube. You can also choose to have the fan point outward rather than directly up into the air. The illustration below shows the fan pointing outward. Having the fan point directly up into the air is a bit better because it's less obtrusive.

Filter brands to potentially avoid

Variations

5-filter version

Rather than placing a piece of cardboard on the bottom side of the cube, another filter can be added in place of the cardboard.  In this case, you would want to raise the cube off the ground (without blocking the entire bottom filter) so that the bottom filter could be utilized.  This would in theory lead to even less resistance on each of the filters, potentially prolonging the life of the cube or increasing the air output.

Two filter "wedge" design. 

A variation of the air cleaner can be made using two MERV filters (add details). This version is slightly less expensive (2 less filters are needed) and has a slightly smaller footprint.

One filter design, the "classic" DIY box fan air cleaner design.

You can duct tape a single filter to the back of a box fan. In this case there is  more strain on the fan motor, more air resistance and the air cleaning efficacy would not be as great. You would also have to replace the filter on the back of the fan more often. But this design has the advantage of having a low footprint and being the least expensive option.

History

As discussed in his original blog post, the design for the Corsi-Rosenthal Cube was detailed by Jim Rosenthal, CEO of Tex-Air Filters, and was dedicated to Dr. Richard Corsi. Neil Comparetto also detailed a similar design in a popular YouTube video, which he called a "Comparetto Cube."

See also

News / media stories