We’ve all heard that there’s no such thing as a ‘free lunch’; well, the process described in this article can be as similar as possible. Most of us already know the benefits of CO2 enrichment for photosynthesis. To maximize greenhouse and indoor growing potential, supplement with CO2 to maintain a level of approximately 1500 ppm, which may require frequent trips to an industrial gas supplier and/or heavy use of propane or natural gas, and costs related. It is ironic that many indoor growers are venting CO2 to the outdoors from home heaters and hot water heaters, at the same time they are releasing or generating CO2 for an indoor grow room or greenhouse.
Propane and natural gas burn clean enough that small ventless gas appliances have been approved for indoor use. All of these gas burning devices use oxygen (in air) to burn the gas, resulting in by-products of CO2, H2O (moisture) and heat (Reusch). Exhaust from gas appliances can provide 3 essential conditions to maximize growth: humidity, temperature, and CO2 level. Most of the exhaust heat is removed by the furnace heat exchanger or water heater; resulting in a slightly hot exhaust. Photosynthesis for many plants, including marijuana, in a CO2-enriched environment is most efficient around 85 degrees F.
If the exhaust from a large gas heater is diverted into the growing area, there is a very good chance that all the oxygen will be burned or displaced, as well as the CO (carbon monoxide buildup), resulting in conditions of toxic air. With the right equipment, the CO2 from your gas furnace and/or hot water heater exhaust can be safely used to supplement the CO2 used in your grow room. This will save time and money, make plants grow very well, reduce fuel use, and drastically reduce the amount of greenhouse gases released into the environment. Using this technique, you will help prevent global warming while optimizing growing conditions. The key to doing this safely and effectively is to divert enough exhaust from your gas appliance to your grow area to maintain a CO2 level of 1500 ppm and have additional exhaust directed outside.
“The Occupational Safety and Health Administration (OSHA) and the American Conference of Governmental Industrial Hygienists (ACGIH) have set workplace safety standards of 5,000 ppm” and very high levels of CO2 can cause undetectable asphyxiation when O2 in the blood it is replaced by CO2 (Minnesota Department of Health). Keep a CO (carbon monoxide) detector in the grow room for safety in case the equipment malfunctions! Do not attempt this project if you use oil or kerosene heat, which do not burn cleanly!
The trick to taking advantage of this source of unused CO2 from gas furnaces and water heaters is electric dampers. A power damper is a section of duct with a flap that turns flow through the duct on and off and is powered by electricity. Some snubbers close with current applied and others are designed to open. Most snubbers are low voltage, so the correct size transformer must be connected in-line to the snubber; there are some 110 volt snubbers. Quality shocks seal much better than cheap shocks. This simple addition to a CO2 enrichment system will pay for itself many times over (especially at today’s fuel prices) and reduce the emissions from the home or business to the environment, making your project “greener”. It is necessary to have a CO2 level monitor connected to a controller (sequencer) to tell the dampers (by applying power) when CO2 is needed and when the threshold has been reached. You can still use your controller to run your CO2 generator and/or regulator.
Find the exhaust pipe of your gas furnace or water heater. These devices should already be properly ventilated. Turn off your gas appliance while you work on this. Disconnect (or cut) a section of conduit where it will be closest, with fewer bends, to connect and route new conduit to the growing area. The few necessary items can be found at most heating supply stores. If you can’t find dampers to match the size and type of duct you have, you may need to convert the duct to a size or type that you can find dampers for. Using a “Y” connector and a power snubber that closes when power is added, connect in-line with conduit running to the outside. For even flow, install “Y” so that the exhaust is at the “bottom” of the “Y” duct section. Now take the damper that opens when power is applied, connect it to the other “Y” opening. Run conduit from this electric opener to the growing area above the plants, as CO2 is heavier than air; but you probably already know this. Now all you have to do is wire the dampers together or use a multi-outlet adapter and connect them to your CO2 sequencer along with your CO2 generator or CO2 tank regulator using a 3-outlet adapter.
If the pipes are away from the exterior wall or ceiling, there may be ducted booster fans in line. If the grow room does not receive flow through the new duct, an inline duct booster fan may be needed, especially if one is used on the original duct that goes outside beyond the new “Y” section. of the apparatus. If you add a duct booster fan, wire or plug it in together with the dampers, then they will turn on and off together. Many furnaces will have a suitable exhaust fan, so an additional auxiliary duct fan will not be necessary. Keep an eye on the booster fans (if any) in the original duct between the Y-joint and the outside, there is a chance they will overheat if they run when the damper to the outside is closed.
Once this is set, when your CO2 sequencer determines it’s time to add CO2 to the room and turns on, the exhaust hatch to the outside will close and the grow room hatch will open; resulting in exhaust from the furnace or water heater being diverted into the grow room. The CO2 generator or release damper will also work, this ensures that the room will always have just the right amount of CO2, even if the furnace or hot water heater is not currently in use. When the proper level is reached and the sequencer is turned off, the door leading to the grow room will close and the door to the duct leading outside will reopen. All exhaust gases at this point will go outside until the room needs more CO2.
For safety, make sure all circuits and/or outlets do not supply more than 80% of their rated wattage and are properly wired. Also, be sure to secure the conduit well. 200°F rated duct tape holds up better than regular (for connecting sections of ductwork).
If you are considering exhausting the water heater for this CO2 enrichment supplement, you can take even more advantage of this setup by timing your showers, dishes, and laundry, when the lights come on (time when the enrichment equipment is running the most) and during the general light cycle.
With this system, growers will find that they make fewer trips to fill their propane or CO2 tanks and spend less money, while the levels in the grow room remain the same.
This addition to an enrichment system will also reduce the volume of CO2 released into the environment from the home or business. The CO2 diverted into the room is used by the plants during photosynthesis, further reducing the release of CO2 from the gas appliance to the environment. With this system, the room will reach the desired CO2 level faster and fluctuate less, further improving growth.
Works Cited List:
Minnesota Department of Health
This page, located on the Minnesota Department of Health website, is a good source for showing the adverse health effects of high C02 levels. As far as I can tell, this site is run by the state government. The information on this page is consistent with other sources that also describe the harmful health effects caused by too much CO2 in the air. This page, while short, clearly presents figures and dangers, agreed upon by government scientists, that are associated with high CO2 levels. The statement, “At very high levels, 30,000 ppm and above, CO2 can cause asphyxiation as it replaces the oxygen in our blood.” clearly demonstrates the potentially fatal condition that elevated CO2 levels can cause.
“Carbon Dioxide (CO2)” Minnesota Department of Health. March 2004.
June 27, 2005 http://www.health.state.mn.us/divs/eh/indoorair/co2/>
Reuch, William. “Reaction of Alkanes” Michigan State University
This page clearly describes the physical process of propane combustion. After reviewing a dozen sources of propane and natural gas combustion, I found this page to have the most accurate, in-depth, yet understandable descriptions of the possible reactions of propane combustion. Although the article does not cite references for the information it contains, the information is consistent with common knowledge and other reference materials and is found on the Michigan State University Department of Chemistry website. By showing the structural formulas for the reactions mentioned along with a clear reasoning demonstrating why the reactions may differ, this source will allow the reader of my essay to understand what products can be created by burning propane. This article shows how CO2 and H2O are the direct products of burning propane when sufficient O2 is present.
Reuch, William. “Reactions of Alkanes” Michigan State University
Department of Chemistry 1999. rev. 2004. June 28, 2005