I am an engineering student at a top 10 engineering school and I am not involved in any illegal activities. I do like to tinker and I am currently growing vegetables hydroponically and looking for a CO2 solution. I have a catalytic camp heater from Coleman camping gear that I got at wally-world for $30 (sportcat model) and I am interested in determining the feasibility of using it to generate CO2 for my veggies. It is a heater that produces mostly CO2 and H20. I post my comments here as I believe you guys are FAR MORE INTERESTED in getting everything you can out of hydroponics than the average veggie grower and I keep running into the problem that every source of knowledge in the other world of hydroponics is far more interested in selling me a $400 CO2 setup than entertaining my ingenuity. I have been a long time reader of this site but this is my first time posting, I had a much shorter version of this but since it took a few hours for my new account to be approved I expanded my research. ENJOY! Please investigate my findings and let me know what you think. Given: ------------------------------ .03% = 300ppm standard atm .15% = 1500ppm desired atm .12% = 1200ppm desired ADD A 3000 BTU camping heater running off a 1lb bottle of propane runs aprox 6.5hrs Combustion analysis of the operating camp heater by the consumer product safety commission determined the average CO2 in the product at ~ 5.25% (Source = https://www.cpsc.gov/library/foia/foia05/os/CO03.pdf) Test Chamber Volume = 100ft3 (Roughly 6ft x 4ft x4ft) - At air exchange rate of .1 x Volume of container per hour, CO2 built up to 8.8% total atm concentration (88,000ppm) - At air exchange rate of 1 x Volume of container per hour, CO2 built up to 3.4% total atm concentration (34,000ppm) - At air exchange rate of 1.5 x Volume of container per hour, CO2 built up to 2.3% total atm concentration (23,000ppm) Note: without adequate air exchange (O2%) the cat heaters will vary their rates of production. These tests were ran until the bottles were empty with readings taken at 30 second intervals. Calculated Air Exchange rate required to maintain 16% O2 (required for proper catalytic combustion) per 100ft3: .5 (air changes per hour) = 1220BTU 1.0(air changes per hour) = 2450BTU 1.5(air changes per hour) = 3700BTU --------------------------------------------------------------- Lets use some math and figure out how to get 1500ppm (.15%) CO2 in a 100ft3 growing box. I will assume an air exchange rate of 1 x Volume of container per hour (throttling a fan to adjust adequately during dosing) This will give me a rate of 34,000ppm max CO2.. WAY TO HIGH How to get it down? - You could increase circulation; it would not affect the addition rate much as there is already adequate O2. Air Exchange is a function (1/hr) so the variable "x" would be the # of times the volume of your grow room was ventilated in an hour. Running a heater at 3000 BTU Rating at x=1 (1 air exch per hr) would be MAINTAINING (not adding) 34,000ppm. Using math alone, the same heater at x=1.5 would be maintaining 22,666 ppm, now lets compare that to the experiment above, which experimentally determined through the process of combustion analysis that value to be ~ 23,000ppm. That is a math to experimental error ratio of ONLY 1%!! Any scientist will tell you that is AWSOME accuracy!! So with this information we can conclude that to maintain 1500ppm CO2 with a 3000BTU heater we must exchange the air volume of the grow room 22.67 times an hour. Sound crazy? Its not too bad, but remember this is not exactly a linear function (i.e. 100% fresh air in does not equal 100% old air out, its more of a mix down but with say an inlet fan at the very bottom of the container and an exit at the very top this will be closer to an accurate linear relationship, it would be worst if the intake and exhaust were right next to each other). For the purpose of hypothesis I will assume it is linear and then experiment. I will assume that I need to put 22.67 times 100ft3 of air thru my 100ft3 experimental grow room every 60 minutes---> that’s 37.78 CFM. See, it’s not so bad! --------------------- How can we make it better? Cycle timing of course but that is the pain with regular bottled CO2. I like things cheap and easy. As far as cost effective, get a 30lb bottle of propane and the $5 adapter for camping fittings, you will save a heap of money. Also, buy the smallest cat heater available. Coleman has a "COLEMAN SURVIVAL CAT EMERGENCY HEATER PREPAREDNESS KIT model #5034-729" $20 800 BTU catalytic heater that runs 27 hours on 1lb of propane. If you were flowering your plants on 12/12 sched and wanted peak CO2 for the lighted 12hrs you would be using 3lbs of propane a week, or about one 30lb bottle of propane (refills are what, $15?) every 10 weeks! Not too shabby on the cost effective side is it?? And 800BTU's is pretty easy to get rid of. By my calculation this 800btu heater could maintain a 600ft3 grow area (about 10x10x6 grow room). A little more tinkering could yield FAR GREATER run times, such as installing an electronic ignition system and setting a timer to only keep it going in short periods to compliment your vent cycles. This would be much like the $400 and up commercial models but cost less than $50 to build, plus the commercial ones don’t come in “closet” size. At this time, however, I suggest just balancing your airflows to maintain PPM and dissipate the near negligible 800btu this thing puts out (Coleman advertises that the unit is CAPABLE of increasing the inside of a car's temperature by up to 10 degrees F.. so a constantly vented grow room thats already pretty warm, only a couple degrees). It’s easier and cheaper initially so it’s what I will be doing. I have a 1500BTU unit sitting a few inches from my intake fan and it has not caused any temperature change. ------------------------ Shopping list: 1 x COLEMAN SURVIVAL CAT EMERGENCY HEATER PREPAREDNESS KIT model #5034-729 ~$20 1 x 30lb Propane bottle ~ $30 (refills $15) 1 x Camp gas adapter (look for it in the camping section) ($5) [Or you could by a bunch of little camp gas bottles, you can also get a fitting for the big tanks to fill the little ones] I’m going to test this to see if it is all you need to deliver a maximum and safe value of CO2 to your grow room for over 10 weeks! I ordered an old surplus atmospheric analyzer with a CO2 ppm meter last week off of Ebay for $25 and will begin experiments as soon as DHL sets it on my doorstep. You shouldn’t need this really once I figure out if the calculations are correct. Most the bottled CO2 users’ don’t use one anyway. My hope is that I can test and prove my theoretical formulas and give you all my experimental data to review. By that point I should be able to calculate a table (or give you a formula) to determine exactly how much ventilation (CFM) you need to maintain in various sizes of grow rooms with nothing more than a $20 camping heater and a propane bottle. It should be low maintenance (lit and secured daily with the light cycle, bottle changed every 10 weeks or so). This could be simplified even more with an electric start camp heater wired to a timer on cycle with the lights. Final thought - In bottled CO2 systems CO2 levels are NOT "maintained," they are simply added to and subtracted from near haphazardly on a very irregular basis. This system would actually "maintain" CO2 levels at a desired concentration ALL DAY LONG. There is a bunch of snake oil and BS in the world of hydro but I think this will be a big difference in yield with very little cost, risk, or trouble. Please post comments, questions, concerns!