I am imagining my hypothetical growroom and wondering how to properly seal access doors. There are zippers and velcro, double sided tape and framed rubber-edged hard doors. I think those are all the options...

Anyway, do the cheap (velcro or zippers) seal well enough to keep the CO2 inside the grow environment and not in a living space?

When your constructing your grow room ensure that there is a vapor barrier around the room, prior to sealing it with the drywall and floor boards.

Post construction you could do similar but man would it be messy imho. You could put a hydro hut in a similar sized closet for example.

This is just reason to plan your rooms well. Best of luck.

CO2 is a heavy gas that usually must be exhausted out of a grow room. It is not much of a leaker. Go to the lowest unvented place in your home and that is where the CO2 level will be greatest (basement/cellar/crawl space. The attic will have the lowest concentration of CO2 ie the major portion of CO2 lost from unvented grow rooms is lost under the door going into the grow room. Woithout a fan pushing the CO2 in the grow room abck up to the ti op of the room the majority of pied in or genearted c CO2 will be at the floor level. Sad situation without a fan as roots need oxygen not CO2 and the plant canopy needs the CO2.

Yeah I'm sorry guys, either you both misunderstood me or I did a poor job explaining what I meant (probably). I am reasonably handy and can build a airtight room-within-a-room. I am just wondering about the access point aka door. Is velcro or a zipper enough of a seal around the doors for CO2 not to leak out into the living space? And yes I would have fans moving the air all around making sure the heavier gas wouldn't settle to the floor.

Foam works great for making a room air tight. At wal-mart they sell a camping foam cusion that is about a 1/2" thick in sporting goods with the camping gear. You can cut and attach it to your wood door to make it more air tight. My door is 1 1/2' by 2' and in the ceiling so that helps me with CO2.

I have never seen zip lock large enough for a door way. Are you talking a tent type grow room or a room of framed walls? with a tent type you have to deal with waht you get pretty much unless you want to hand another sheet of plastic over your entire door ways so you have tow layers of plastic instaed odf one. Just make te outter sheet larget than the doorway so there is plenty of overlap. With a framed wall just use a preframed exterior door that comes with weather stripping or add weather stripping to an existing door. Again most leakage would be under the door. If you are just trying to avoid the cost of a door on a framed wall room just hang plastic sheeting over both the inside and the outside of the door way. The high tech method is to use an air curtain. This is a squirrel cage fan a bit wider than the door that blows air down infront of the door way. These are very ogten used on walk in freezer doors and used in laboratories and laboratoriy vent hoods. In ti op of the line greenhouses (unversities and reserach) they are used in all exterior doors as the doors can be open and insects and pollen etc can not go through the air curtain. Theu y also contain odors. Here is one on eaby. http://cgi.ebay.com/FlowPro-Air-Curtain-...id=p3286.c0.m14 That prices is about 20% to 30% of retail.