I use the tank method . I where a mask and just turn off all the fans and air conditioner then I open up the c02 tamk and try to close the door as much as i can while I feel the roo with the desired amount. Then I reture the air and fans because c02 i heavier than oygen so I want the fans below to blow the c02 upwwards . I then seal my room I mean windows and the crack under the door for like 3 hours, then I open it up and givefresh air. I also raise the temp to about 85-90 while co2 . Then I air them out and place the temps back. Yes this is crude way to to it buit it is cheap. They never sweat me at the welding store i feel my 10 # tank at. good luck!