"if you vent a c02 filled room into another part of the house is there a danger of filling the house with co2"
I am also looking at setting up CO2. One of the most important things when doing so is making sure the grow area is properly sealed. If it is not you will be letting the CO2 leak into the rest of the house where it does nothing good. As long as you are investing in this idea make sure you do it right. Since you have air cooled hoods it seems like a good start. If you are not sure if the hoods are airtight you can apply some of that silver coated duct tape where the hood meets the glass. Hope this helps!