Quick answer: a CO2 generator for a greenhouse raises the carbon dioxide level in your growing space so photosynthesis is not bottlenecked by ambient air, which sits near 420 ppm. Growers commonly enrich to roughly two to three times that level, and the right generator depends on how your greenhouse is built: burners that run on propane or natural gas suit sealed winter houses, tanked CO2 with a regulator and timer suits spaces where open flame is a bad idea, and small electric units suit hobby benches. This guide walks through how each type works, how to size one to your square footage, and the safety steps that come before any purchase.
What a CO2 generator actually does for plants
Plants build their tissue out of CO2 and water using light energy. In a closed greenhouse, a dense canopy on a bright day can pull the CO2 level well below ambient within a couple of hours, and growth slows even when light, temperature, and nutrients are all fine. Enrichment removes that ceiling. The effect is best documented in bright conditions with healthy plants; a dim, poorly ventilated greenhouse with stressed plants will not see the same return, because CO2 stops being the limiting factor.
Timing matters as much as level. Enrichment pays off during the hours when light is strong and the house is closed up, which in practice means cold-month production growers get the most from it. In summer, when vents and roll-up sides are open all day, injected CO2 leaves with the air, and most growers stop enriching rather than pay to fertilize the neighborhood.
The three types of CO2 generator, and who each one fits
Propane and natural gas burners. These burn fuel to produce CO2, water vapor, and heat. They are the workhorse choice for commercial houses and serious hobbyists running through winter, because one unit covers a large volume and the heat is a bonus rather than waste. The trade-offs are real: an open flame, oxygen consumption, and combustion byproducts mean you need a clean-burning unit, fresh air makeup, and a CO monitor in the house. If you already handle propane for other equipment, the propane generator guide on this site covers tank sizing and placement rules that apply here too.
Tanked CO2 with regulator, solenoid, and timer. A cylinder of compressed CO2, a pressure regulator, a solenoid valve, and a simple timer or controller inject gas on a schedule. Nothing burns, so these fit greenhouses attached to homes, school projects, and any space where a flame or added heat is unacceptable. Running cost is per cylinder refill, and the cylinders are heavy, so plan where they sit before you buy. This is the most common recommendation for growers enriching spaces under roughly 500 square feet.
Electric and catalytic units. Small electric CO2 generators and catalytic burners occupy the middle ground: no open flame to babysit, lower output, and prices that suit bench-scale growing. Output is modest, so match the rated coverage to your actual enclosed volume, not the seller's optimistic headline.
A note on the cheap end: dry ice, vinegar-and-baking-soda kits, and mushroom-block fermentation all produce CO2, and all of them belong in the experiment category rather than production. They work for a school windowsill, not for a house you sell out of.
Sizing by greenhouse area, honestly
Sellers quote coverage in square feet, but CO2 fills volume, so a tall commercial house needs more gas than a low tunnel of the same floor area. A practical approach: take your floor area, note your average roof height, and buy for the resulting cubic feet with headroom. For burner units, the BTU rating drives both CO2 output and heat; in a small hobby house, an oversized burner will cook your plants before lunch, and thermostatic or modulating controls are worth the extra cost. For tanked systems, the number that matters is how many refills a season of enrichment will take, which follows from your house volume and target ppm.
Sealing quality changes everything. A house with gaps at the foundation, a leaky door, or constantly open vents will bleed enriched air faster than the generator can replace it, and the honest move is to tighten the enclosure before buying a bigger unit. Enrichment and ventilation are opposites by design, so plan for the months when the house stays closed.
Safety steps that come before the purchase
Burning fuel in a sealed space is the part that deserves respect. Before running any burner:
- Fit a CO monitor at plant level, not on the ridge, and test it with the generator running.
- Keep a fresh-air inlet, however small, so combustion does not starve for oxygen.
- Follow the clearances in the unit manual to combustible benching and plastic coverings.
- Store propane cylinders outdoors or per code, never inside the growing space.
Tanked CO2 has its own rules: chain cylinders upright, use the correct regulator rather than improvising, and ventilate before working in the house after a long injection cycle, since heavy CO2 settles low and displaces breathable air. None of this is exotic; it is the same discipline portable generator owners follow for exhaust, just applied to a growing space.
FAQ
Will a CO2 generator work in a small greenhouse or grow tent?
Yes, and small sealed spaces are actually where enrichment shows results fastest, because the volume is cheap to fill. A tanked system with a timer is usually the better fit than a burner, which produces more heat than a small space can absorb.
How much does CO2 enrichment increase growth?
Honest answer: it depends on light, temperature, and how healthy your plants already are. In bright, well-run houses, enrichment to roughly two to three times ambient is a standard production practice; in dim or poorly managed spaces, the gain shrinks toward zero because something else is the limiting factor.
Is a propane CO2 burner safe to run overnight?
Only with the right controls. Clean-burning units with oxygen-depletion shutoffs, a working CO monitor, and adequate makeup air are run overnight in commercial settings. If any of those three is missing, run the burner while you are present and enrich with tanked CO2 at night instead.
Does this site's generator sizing calculator apply to CO2 units?
The generator size calculator is built for electrical load, not gas, so use it for backup-power questions. For CO2, size by enclosed volume and target ppm as described above, not by watts.
Where to buy
Burner and tanked systems are sold through greenhouse supply specialists, and comparison shoppers can check current CO2 generator listings on Amazon or the regulator and controller category on Amazon. For the background on how similar fuel-burning appliances are handled in home settings, see the ozone generator for house piece and the general where to buy generators guide.
A CO2 generator for greenhouse growing is a straightforward purchase once you know your enclosed volume, your sealing quality, and whether an open flame is acceptable in the space. Size for the closed season, respect the combustion rules, and enrichment becomes one more dial you turn toward better yields.
