Odorless Cat Litter Box

Cat litter boxes stink to high heaven. Worse, many cat owners gradually acclimate to the odor, creating an awkward situation for house guests. If you are a cat owner, this DIY catbox ventilation system will dramatically improve the quality of your life, restore your fraying friendships, and amuse guests with your ingenuity. Your cats will probably even forgive you for not scooping as often.

This design is intended for those who are willing to keep the litter box near a single-hung window with outer screening and no burglary concerns (i.e. probably not on the ground floor in a neighborhood like mine!). I will be following up this post with another version that couples to a bathroom exhaust vent.

This project is designed to cost less than $35 to make, and uses mostly common, recycled and/or re-purposed and cheap materials. It is also quite doable for someone with limited tools. Perfect for apartment dwellers!

Required Tools
* Hot glue gun and roughly 10 hot glue sticks
* Heavy duty poultry shears or tin snips
* Serrated bread knife
* Serrated tomato knife
* Electric drill
* Standard drill bit index (up to 1/2")
* Permanent marker

Required Materials
* Hooded plastic cat litter box with at least 7"x7" of flat surface on the back end
* 12V 120mm CPU fan (smaller sizes may also work...try recycling one from an old desktop computer). I used this one.
* 12V DC power adapter (500ma). I used this one.
* 2 x plastic food storage containers (25oz, 740ml - 6-3/4" x 6-3/4" x 2-1/4") with lids
* 2 x empty, de-labeled 28oz food cans (I used cans from crushed tomatoes) with both ends removed.
* approx. 10 hot glue sticks
* 5-25' (location dependent) of 4" dryer duct, aluminum or plastic
* electrical tape
* 2 x 16" long zip ties
* 2 small zip ties
* 8" x 36" rectangle of Owens-Corning Foamular(R) 250 or comparable (pink foundation insulation) or 3/4" plywood (if you have a jigsaw or sawzall).

Most hooded litter boxes have these silly "air filters" that slide into openings on the top-back of the hood and look like grey pot-scrubbing pads.  They do nothing to remove any of the smells...pure gimmick.  With our new fan-exhaust system, we will want air to draw in from the front opening of the hood, across the litter, and out the back.  Because the vents that come with the catbox are positioned at the top back of the cat-box, we will want to cover them to improve airflow from front to back.  Trace their exact shape on some corrugated cardboard twice, so you can have a double thickness to match the thickness of the filter slot.  Insert and trim.  

Large empty food cans (28oz) are close enough in diameter to be re-purposed into a great adapter for standard 4" flexible dryer duct hose.  Tin snips or well-made, heavy-duty poultry shears easily cut through the can.  Combine with a standard square disposable 25oz plastic leftover / freezer container and some generous beads of hot glue to seal the deal, and for around $1 you have effectively built a dryer duct flange.  Keep the container lid handy as we will use it later as an an air-tight coupling mount on the back of the catbox.

Get to know your fan and understand it's directionality and the polarity of your 12V adapter so you can be sure your are facing the fan the correct direction when you glue it into the leftover container part of your home-made dryer duct adapter. Strip the ends of the leads and conntect them to your power adapter.  If the fan doesn't run at first, reverse the leads on the adapter, as polarity seems to matter on these fans. Face the fan so that it will blow OUT of the the can side of the duct flange. Cut a small slit in the side of the container closest to the wire leads for the fan and pass them through.  Use four generous blobs of hot glue and press and hold the fan firmly in place until the glue hardens.  Use another blob of hot glue to seal and secure the wire leads passing through the container.  Strip the leads of both the power adapter and the fan.  Twist connections and wrap with electrical tape.  Tie a knot in the wire above the wire splice to provide stress protection in the cord.

The lid to the leftover container is going to serve as a kind of airtight coupling that will hold and seal the hose adapter / fan unit on the back of the cat litter box.  Use a permanent marker to outline the container lid in the center of the flat plastic back of the litter box hood.  Get your glue gun good and hot and have several extra glue sticks on hand.  Run a generous bead of hot glue just inside the permanent marker line so that it will create an airtight seal with the lid.  Press the lid firmly on the hot glue until it sets.  Press the center of the lid to listen for air leaks from the air trapped between the food container lid and the plastic litter box.  Most likely you will need to run several more beads of hot glue around the edge of the container lid to seal it to the litter box.

Once you are satisfied with the seal between the container lid and the back of the catbox, use your shears to cut away a square-ish, roughly 5"x5" center from the lid. Put another bead of hot glue around the inside of the container-lid / catbox-hood joint. Grab your drill and a large (1/2" is what I used) drillbit. Improvise a regular pattern of holes covering the area inside the cut out area, leaving only enough of a plastic to create a barrier that will prevent your cat's tail or fur from being drawn into the whirring fan blades, but that allows for a maximum of air flow. Use your shears to clean up the holes. Check that your homemade fan housing / hose adapter fits snugly onto the litter box. You may eventually choose to glue the assembly together. I chose to leave mine removable so the hood can be easily cleaned with water without damaging the fan.

Because most apartment dwellers don't have ready access to electric saws, I opted to use 1" thick Owens-Corning pink foundation insulation: it can be easily cut with a serrated bread knife.  I bought a whole sheet of it for pretty cheap at a Home Depot in the Bronx and cut it down some using a handsaw in the store to allow me to get it on public transit.   The pink insulation could probably be painted with acrylic wall paint to improve appearance.  Another bonus is that it provides insulation comparable or better than window glass.

Use a tape measure to to get the inside dimensions of the track that your lower double-hung window slides in.  Use a straight edge to mark a rectangle 8" by the width of your window frame.   Use a large, serrated knife to cut the rectangle from the stock.  Be sure to support the material as you cut, as it cracks somewhat easily.

Test the fit of the foam in the window and trim accordingly.  I had to compress the foam some with the palm of my hand to get it to fit in the window track, but it's going to make a really tight seal against the cold NYC winters as a result!   I also found that the seal with the window was improved by using the tongue side of the tongue-and groove as the top edge of the window insert.

You're essentially going to be making a home-made version of a through-wall dryer exhaust vent. If money is no object and you don't want the fuss, there are kits available for this in most corner hardware stores. Homeowners may also prefer a less homespun approach or a through-wall option, which is afforded by the long duct collar on most commercially available duct vent kits.

Nevertheless, you want the affordability, challenge and fun of re-making this with tin cans and tupperware, read on! It's important that our design keep out the rain and wind, so we're going to use a 2nd leftover container and lid to build a rain/weather hood, with a backdraft-preventer flap made from the extra center stock we cut earlier while making the fan housing. To connect the flap with small zip-ties, drill two small holes per side in the lid and one larger hole per side in the flap and pass the zip-ties through as shown in the photos. The zip ties should pass easily through the flap, allowing it to hang and swing freely.

Note that the container bottom is going to serve as a rain hood on the outside of the window divider. Cut a rectangular portion out of one side of the container, which will face downwards, allowing air to escape. (See last several photos for detail)

Position the litter box in your space and determine the best location for the dryer duct to pass through the window insert. Trace the outline of the can on the insert to suit your chosen location.  Remove the insert from the window and use a large (1/2" or so) drill bit to perforate the inner perimeter of the circle.  Use a serrated knife to gently cut a clean circle from the foam.  Insert the vent through the foam to test the fit.  Clean the hole as needed.  Trace the outline of the container lid on the foam in its fully-inserted position.  Run a thick bead of hot glue around the inner perimeter of the traced line. Press and hold the lid against the foam until the glue sets.  Now glue the bottom of the food container into the lid.  From the inside of the window insert, inject blobs of glue around the body of the can to help hold it in place.  Install the window-insert and cinch down the duct using a large zip tie.  

Plug in, kick back, and enjoy an odorless litter box!  I enjoyed creating some smoke with burning paper just to observe the draft of air passing through the mouth of the litter box hood and out the window.  

Some cats can be extremely finicky about changes or slight noise in the cat-box, and may start crapping all over the place as a result.  If this ends up being the case, you might consider tweaking this design to put the fan on the window-end of the system.   If you want a further challenge, try rigging up two PIR sensors with an Arduino and a relay switch for the fan like I did for my Mom.  The fan shuts off whenever the cat comes near the litter box, and stays off for 30 seconds after the last detected motion.  Problem solved! Lot's of fun.

If you prefer to have the litter box in a bathroom, you can build a homemade hose coupling that fits over the bathroom exhaust fan / vent.  Because 4" duct is a bit unsightly snaking up to the ceiling, it's probably worth using a design with smaller diameter hose, like 2.5" sump pump hose.  Smaller cans, like those used for tomato paste, could provide the way here...