Window Exhaust Box Concept on Paper
The Airbrush Paint Booth is designed to capture all of the air contaminated by harmful vapors during the painting process and keep them out of the indoor breathable air supply. The design of the Paint Booth itself has to be functional and efficient. Once captured by the ventilation process, there must be a seamless flow to export the contaminated air to the outside. This is where the Paint Booth Window Exhaust Box comes in.
The fan exhaust is a 3-inch diameter pipe which can easily connect to 3-inch foil dryer duct. While this duct could be run to the outside through an open door or window, that would leave an opening that would allow outside air (even the exported contaminated air) to flow freely into the indoor environment where painting is taking place.
I decided that the logical exit port should be a window as it could be closed tightly around an exhaust panel that was sized properly. Off to Home Depot I went to examine available components and formulate the design. There is enough wood left over from the 4'x8' piece of plywood used to construct the paint booth itself, so additional wood was not needed. I also had on-hand a 16-inch by 4-inch vent panel that I had purchased earlier for the paint booth but ended up not using. This also will fit into the Exhaust Box design.
Additional materials purchased for the exhaust box were:
1) One 3-inch x 25-foot flexible aluminum foil duct
2) One 3-inch to 4-inch diameter duct increaser
3) One 4-inch diameter louvered exhaust hood (6" x 6")
4) Two 3-inch adjustable metal worm gear clamps
Next I picked a window and took some measurements. It is important to note that the dimensional specifications in the below design are specific to fit the window frame opening that I will be using. If you will be building a window exhaust box, you will need to adjust as appropriate to fit your window design and opening.
The width of the main window opening is 32 inches. This 32 inch width which fits snugly under the raised window and fits flush against a slightly narrower external opening. This will make it very easy to seal off the outside air from the room interior.
Looking at the hardware components and sill/frame outline, I decided that a height of 12 inches would be appropriate for the design of the Window Exhaust Box.
Rather than free-handing the design drawing like I did for the Paint Booth, I decided to use PowerPoint for the below drawings. These drawings are NOT to scale! Hopefully they are easy to understand:
Drawing 1 - Exterior Window Panel
The exterior window panel is the largest component. This is the exterior wood face of the Exhaust Box that fits snugly into the window opening. This window opens by lifting the bottom window upward. The bottom and two sides will be surrounded by the window frame. Once in place, the window can be lowered until it contacts the top of this panel, completing the seal between the outside and the inside.
The 16-inch by 4-inch vent cover is the only piece of hardware that will be attached to this panel. This vent will be cut directly in the center of the panel.
Drawing 2 - Interior Room Panel
Opposing the Exterior Window Panel is the Interior Room Panel. This panel does not need to be as wide as the window panel, but it does need to be wide enough for a connecting chamber to be built between the two panels containing airflow between the two. Therefore the 16-inch wide exterior vent cover and the 6-inch square louver cover will have to be within the dimensions of the inner chamber. I decided that a width of 20 inches and a matching height of 12 inches would be sufficient
Drawing 3 - Exhaust Box Top View
The top view shows how the panels will come together. Airflow from the 3-inch diameter flexible foil duct will enter the chamber via the 3-inch to 4-inch adapter that connects to the 4-inch diameter port of the inward-facing louvered exhaust hood. The louvers open easily in the direction of air-flow and shut when the fan is off keeping small critters outside and sealing off any reverse air flow.
From here the air enters a small chamber that forces the air to exit the window through the 16-inch by 4-inch vent in the exterior window panel.
Drawing 4 - Exhaust Box Side View
The side view reinforces the top view. Measurement of the window revealed that the top of the window sill is actually 1/2-inch lower than the top of the window opening on which the Exterior Window Panel will rest. There is also a 1-inch lip extending upward from the window sill that seals off the bottom edge of the window when it is fully lowered. Therefore, the bottom of the enclosed chamber connecting the interior and exterior panels much be high enough to clear this lip. The interior panel will also be placed 1/2-inch lower than the exterior panel to compensate for the lower sill. This will make sure that the exterior panel is "At Rest" in the snug position in the window opening.
For the purpose of these drawings I have indicated a depth of three inches for the connecting chamber between the two panels. The sill dimensions will allow a total depth of seven inches. As I review the proximity of the Louvered Exhaust Hood to the external vent I ma consider some additional depth - perhaps five inches to reduce the velocity of deflected air off the inside of the external window panel.