Bob's Filter Conversion

How I turned a dump discard into cleaner shop air.

SHOP OWNER: Bob Meehan
LOCATION: New Durham, NH

    This is my homemade shop dust / air filter. I gutted an industrial sized air conditioner I found at the dump. I filled the back with plywood, to it I mounted a three-speed furnace squirrel cage blower that I picked up for free, moved the metal air conditioner breather cover from the rear to the front and sealed perimeter with felt weather strip, made oak filter holders, and off I went. Hanging over my table saw, it clears my 25 by 25 shop in no time. I also used the three-speed switch that was in the original air conditioner to control the blower. It cost me about $15.00 to build.
    Eye bolts with rubber insulators, fender washers, and threaded rod hang the unit nicely from the floor joists. All mating surfaces have a sandwich of felt weather stripping between them to aid in keeping dust from getting to the blower. I made the filter retaining clips from scrap oak and drywall screws. They twist in and out to allow the filter to just pop in and rest in place. Have fun building your own out of scrap. Check with your local HVAC shop for an old forced hot air 115-volt squirrel cage blower. Next, I plan to take our old cloths dryer and make a downdraft sanding table by top-mounting an old Amana grill/cook top exhaust fan I came across on the side of the road! I have a lot of fun making shop helpers from junk!
Bob's Filter Conversion

    Work started by gutting an old commercial-sized air conditioner, I took the protection grate off the rear and plugged the opening with 3/4" plywood mounted with caulking and screws. You can see the four "T" nuts used to mount the inverted blower.
Bob's Filter Conversion

    Then I plugged the left side vent with tin and screws. The perimeter of the tin was caulked. For a better seal and finish paint, I used Frost King rope caulk that I already had in the shop. I used a heat gun to help soften the caulk to lay it flat while screwing down. I filled any remaining holes with pop rivets.
Bob's Filter Conversion

    The right side was used as the exhaust. I attached an HVAC connector box to the blower outlet to set it flush to the side vent. The unit sits on what were discarded packing trusses used by my local motorcycle shop for crating new motorcycles. They were throwing it out! The three-speed switch also came from the air conditioner. The blower came wired for four speeds.
Bob's Filter Conversion

    Here you see the blower inverted and mounted on thick rubber feet to the back plywood. There is a metal hanger, which I added from the top of the blower to the case top, to help with the weight of the side-mounted blower. In addition, the silver grate came from the back of the air conditioner and brought to the front. It makes a great backing for the furnace filter. Otherwise, the blower would collapse the filter when operating. It also is lined with felt to act as an air seal seat for the filter.

. . . Bob Meehan



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