any thoughts on yeast and sugar as a co2 generator?

I currently have a well ventilated 12x15 grow room with 8 foot ceilings. I am using a 600 watt hps and two 45 watt fluorescent lights. I have been experimenting with home made co2 systems. I am currently just using a gallon jug with 2 cups of sugar and a packet of bakers yeast. I am not sure if that is even close to being an effective amount and if not how much would I have to ramp it up? any thoughts? Thanks.
 
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