Well there is three main basic ways of doing CO2 in a garden... the first is the DIY recipes from making beer, to using yeast, sugar, and there are some other one's too... in the end DIY CO2 is the most expensive way of doing it, unless you are that small grower with plants under your kitchen sink. For smaller area's such as yours the next more cost effective way is to run a CO2 bottle of compressed CO2 gas, a bottle (CO2-Gas) will cost you about $120 brand new + shipping, $25-35 to fill each time, and then you'll need a CO2 regulator will set you can about another $100, and then you'll either need to run a CO2 timer or CO2 controller. Personally I like the Sentinel DEC-4 Environmental Controller because it will do all kinds of things including regulate your CO2 between 1300-1500 ppm and you can set it for Day-On, Day Regulate to make it control the CO2 levels for you, or CO2 Night for those growing mushrooms and it'll set you back about $300.
As far as needing to seal your room for CO2 goes, it can be rather straight forward and simple, just buy some heavy plastic at a big box store type of store and seal the seams together with a plastic glue meant for sealing it together, they refer to it as a "vapor barrier" for when you are blowing in insulation so there is a barrier between the sheetrock and the insulation. Otherwise you can use some really strong type of duct tape, but the glue meant to seal that stuff together is by far cheaper to seal the seams. For the doorway, that is where I tell people just to use good quality duct tape and make an "L" door to keep the doorway small to lessen the chances of leaks.
When you seal a room for CO2 the humidity is going to skyrocket and your 5-degree temp rise will be able to build up to a lot more... so you will have both temps and humidity to deal with, on the plus side CO2 gas drops the humidity down by a bit most of the time, and since CO2 is a very cold gas, it also helps to knock down the temps slightly when its going. Another plus side to CO2 is that the plants take off at faster speeds, love higher heat and as long as your LED's have good light penetration you'll really enjoy the benefits.
The third way of doing CO2 is to do a CO2 generator they come in Natural Gas and in Propane and the short of it is simply this, they are said to be for larger spaces because they burn the gas to make the CO2, but are not recommended for living spaces or places where humans or pets would live and sleep because of the danger of CO2 poisoning if they malfunction. Greenhouses if you ever go to one in the summer to buy plants will have these big garage heaters up by the ceiling and while it is hot in there you'll hear it kick on and blow more hot air at you, that is the CO2 burner.
If you are going to run CO2 it's really best to seal the room air tight, unless you are on natural gas for pennies and using a CO2 burner in a building used for growing plants then I can see how they get away with it, When running CO2 bottles or a generator you want the CO2 to come from above the plants because it settles to the floor as it is a heavier gas than air, thus why people put fans on the floor pointing up towards the plant canopy to kick up and stir up the CO2 on the floor so you don't waste it. Its also smart to put the CO2 on a timer as well as a regulator in my thought, let the controller regulate it up until the last hour of light, then shut off the CO2 completely, the plants don't use it when they sleep so why flood the area to 1500 ppm, 5-minutes before the light shuts off just seems like a waste of CO2 that you have to pay for.
Recently with the new Oregon rules on the commercial cannabis industry saying they can not use any pesticides or fungicides on their cannabis plants its entire life cycle, got people talking of how to do that. The answer is simply they have to seal their growing area's air tight, to prevent any pests and such from coming in, then scrubbing the air with a carbon filter and UVC light, it keeps problems from arising, adding CO2 just further adds to more yields and its a Win-Win as it cost more upfront but pays off repeatedly with every harvest.
