We’ve all heard that there is no such thing as a ‘free lunch’; well, the process described in this article can be as close 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 around 1500ppm, this may require frequent trips to an industrial gas supplier and/or heavy use of propane or natural gas, and related costs . It is ironic that many indoor growers are expelling CO2 outdoors from home heaters and hot water heaters, while at the same time releasing or generating CO2 for an indoor grow room or greenhouse.
Propane and natural gas burn clean enough that small, unvented gas appliances have been approved for indoor use. All of these gas burning devices use oxygen (in the air) to burn the gas, resulting in byproducts 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 strong chance that all of the oxygen will be burned or displaced, as well as the CO (carbon monoxide buildup), resulting in toxic conditions from air. With the right equipment, 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 great, reduce fuel use, and dramatically 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 into 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! Don’t try this project if you’re using heat from oil or kerosene, which don’t burn cleanly!
The trick to harnessing this source of unused CO2 from gas furnaces and hot water heaters is electric dampers. A power gate is a section of conduit with a flap that opens and closes the flow through the conduit and is powered by electricity. Some dampers close on applied current 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 shock absorbers. Quality shock absorbers seal much better than cheap shock absorbers. This simple addition to a CO2 enrichment system will pay for itself many times over (especially at today’s fuel prices) and reduce home or business emissions into the environment, making your project “greener”. It is necessary to have a monitor of CO2 levels connected to a controller (sequencer) to indicate to the gates (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 on 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 a new conduit to the growing area. The few items needed can be found at most heating supply stores. If you can’t find dampers that match the size and type of duct you have, you may need to convert the duct to a size or type for which you can find dampers. Using a “Y” connector and a power damper that closes when power is added, connect in-line with the conduit running to the outside. For even flow, install “Y” so that the exhaust arrives 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 a duct from this electric open damper 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 outside wall or ceiling, there may be in-line duct booster fans. 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 runs 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 heaters 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 outdoors, there is a chance they will overheat if they run when the damper to the outdoors is closed.
Once this is set, when your CO2 sequencer determines it is time to add CO2 to the room and turns on, the exhaust damper to the outside will close and the grow room damper will open; resulting in furnace or water heater exhaust being diverted into the grow room. The CO2 generator or release regulator will also work, this ensures that the room will always have just the right amount of CO2, even if the furnace or water heater is not currently in use. When the proper level is reached and the sequencer shuts down, the gate leading to the grow room will close and the gate 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 supply no more than 80% of their rated load in watts 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 duct).
If you are diverting your water heater exhaust for this CO2 enrichment supplement, you can get even more out of this setup by timing your showers, dishes, and laundry, when the lights are on (a time when the enrichment equipment works the most), and during the light cycle in general.
With this system, growers will find 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 plants during photosynthesis, it further reduces the release of CO2 from the gas appliance into the environment. With this system, the room will reach the desired CO2 level faster and fluctuate less, further enhancing growth.
List of works cited:
Minnesota Department of Health
This page, located on the Minnesota Department of Health website, is a good source for showing the adverse health effects caused by high levels of C02. 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 brief, 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 suffocation 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 burning propane. After reviewing a dozen propane and natural gas combustion sources, I found this page to have the most accurate, in-depth, yet understandable descriptions of possible propane combustion reactions. Although the article does not cite references to 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 of the reactions mentioned along with clear reasoning showing why the reactions may differ, this source will enable 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 enough O2 is present.
Reuch, William. “Alkane Reactions” Michigan State University
Department of Chemistry 1999. rev. 2004. June 28, 2005
http://www.cem.msu.edu/~reusch/VirtualText/funcrx1.htm>