I made a housing from scrap material and fabricated two flaps that open when the fan is turned on from the wind velocity. The flaps underside was covered with Roof insulation material. The weight is sufficient to close the opening under gravity when the fan is turned off.
Commercial products available is very expensive. This solution basically cost R100 for the extension lead the rest was fabricated from material that I had available. Total cost for the housing is in the region of R150.
Step 1: Step1: Made Grill From Old Refrigerator Door
For the Grill that will be visible I used the door of an old Bar fridge. I cut a circular hole into the door with an angle grinder. I glued a nylon netting on to it with a glue gun. On the other side i used the racks from the Bar Fridge as support for the Fan to rest on. I spay painted the bottom white.
Step 2: Step2: Bucket to Support Fan
I cut the bottom off an old bucket and used the top portion to support the fan.
Step 3: Step 3: Old High Velocity Fan Placed on Bucket
I removed the stand from an high velocity floor standing fan and placed it on the bucket.
Step 4: Step 4: Housing With Flaps to Prevent Dust to Enter House.
For the Housing it was made out of two parts. Bottom Portion was made from wood and Wrapped with Roof insulation material. Top portion with flaps was made from a piece of foam packaging material. I cut a circular hole in the bottom and made two flaps that i fixed to a hinge and secured with cable ties. I covered the flaps with the roof insulation material to have enough weight to fall into the closed position when the fan is switched off. See video for functioning of the flaps.
Step 5: Step 5: Fitment in Ceiling
To install I replaced one of the two existing Ceiling trap doors. Basically placed all the parts and placed insulation material around it to fill any gaps. The gaps around the Grill will be filled with a piece of wood. I made an extension plug that is plugged into the wall socket for the electrical connection.