This is a home made filter box, including a active carbon filter, for around 260€ all together including the insulating foam and the duck tape i buyed too. Against a filter box from a Grow Store for around 1.000€. (last picture)

Step 1: The Materials

Thoes are the materials i used.
A air filter box, that is used to clean the dust out of the air. I buyed mine one from a gastronomical store including shipping for around 170€. The flange of the filter box is 160 mm. Then a active carbon filter with also a flange of 160 mm (dont be worry, it will fit everything just fine), a volume of 450 m²/h which i got for 70€ from a second hand store but it still was new and unused cause it was a commision ware. At last some insulating foam, duck tape, styrofoam and a litle bit of corrugated cardboard.

Step 2: Make a Socket for the Active Carbon Filter

Use the styrofoam to build a socket that will fit into the box and which will keep the active carbon fitler in place. The corrugated cardboard is used to give the socket more stability, so that the weight of the carbon filter will not squeeze the styrofoam.

Step 3: Insulating and Securing the Back Side

Now put the active carbon filter into the box, place it onto the socket and then take the insulating foam and start to secure the socket from one corner down the side to the ground of the box. If you have any gaps between the socket and the box it will also fill out thoes gaps and secure the whole thing. Do the same on the other side too and then connect both corners with each other. That will be enough for the socket. To secure the carbon filter, just spray a line of the insulating foam under it where it lays on the socket and then spray something of the foam onto the filter down to the socket, connecting it with the line you just previous made. This will be enough for the back side and you need to wait around 4 hours (depending on the foam you used) till it will be hardened and ready for using.

Step 4: Insualting and Securing the Front Side

Do the same you did to the back side now to the front side. Secure the socket down to the box. Then insulate the inside flang between active carbon filer and the box it self, around the carbon filter just like you can see in the pictures. If there are any gaps between the filter and the box then they will be filled out with this. That way we have done twoo things to same time. Insulating the entry of the airflow where the smelly air will be throwen into the carbon filter and securing the filter it self. After the front and the back side are hardened you could even turn the box upside down. But i wouldn't recommend that. ^^

Step 5: Insulating the Littel Gap on the Front

To be on secure side, we use the Duck Tape and also insulate the gap between carbon filter and air box on the air flow entry on the outside. Normally this isn't really necessary in case of the insulating foam we sprayed around the carbon filter and the box it self. But it doesn't hurt, it doesn't cost a furtune and if we do something we do it right or we just leave it. :P

Step 6: Fire It Up

As soon everything is hardened and insulated put the cover onto it and close the box. You are ready for action now and able to throw the filtered, hot air outside your living room. For a price that is acceptable and not do cost you a diamond ring for your girlfrind :) :D