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Catalyst Heaters for cheap CO2 in small grow rooms?

Discussion in 'Basic Growing' started by Aaron385, Jun 1, 2006.

  1. Aaron385

    Aaron385 Registered

    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.

    .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 =

    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 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!
  2. Zandor

    Zandor Registered+

    I don't have the time to read it all but I have read enough to chime in I believe.

    What about leakage?

    What about plant usage?

    Yes burning a blue flame will produce CO² but how would you regulate the exchange of gas vs. heat?

    You math looks like it assumes everything is perfect and in a sealed environment. If you can produce CO² at that level and you may I did not bother to recheck your math I assumed it was right. You may have just left off a few variables. The idea of using enhanced CO² is to raise the level to (X) I prefer to add 1500ppm to raise the level to 1800ppm then hold it there for 4-6 hours only refilling it when the level drops more then 100ppm. Exchange the air once every 6 hours and start all over again.

    I also assume you know that for growing indoors you must have HID lights so the plant can process the extra amount of CO²?

    Fluorescents lights do not produce enough light for the plant to process the extra amount of CO²
  3. Aaron385

    Aaron385 Registered

    Thank you for the chime in!

    In that post (sorry about the length) I describe a "feed and bleed" system if you will. The burner runs during the light cycle constantly and the atmosphere is exchanged at a rate that maintains proper ppm. Leekage and plant usage doesnt play much into the equation since it is a feed and bleed system once the equilibrium is established (i.e. you find the right fan speed setting to keep atmospere at desired ppm)

    These are not blue flame burners, it is a 100% catalitic reaction. Heat is released, but with only 800 BTU to get rid of the fan speed should do the trick.. I have also considered mounting a few feet of 4" drier duckting to the burner so I can put it a few feet from the grow area and have my intake fan sucking on it. The metal ducting should also dissipate a good bit of the heat.

    What I have been doing since I imagined this up last night is just setting a burner in the closet that has the grow room in it. My actual grow room is only about 50sq ft in about a 120 sq ft closet and I typically leave the big doors of the closet open with a fan cirulating air in and out of the closet and the A/C vents in the house slightly throttled to give the room a little more A/C .

    When I lite the burner I close the closet door and let it run to fill up the closet outside of the growing chamber (and inside as it circulates). Since I am still waiting on my atmospheric analizer to be delivered I only run the burner for a few (~10) minutes at a time as not to overdo the ppm CO2. I am getting about a 1-1.5 degree rise in temp while the unit is on and then I shut it off (stick my arm in the closet, hit the switch, shut the door asap) and let the CO2 circulate while I watch room temps on my $20 wireless indoor/outdoor thermometer in the other room (the "outdoor" sensor is in the grow room). Temps climb another few degrees over the next hour or two due to the lights but stay well within limits. When room temp gets to about 83F I open the closet door and let it circulate out.

    Once I have the meter I will be able to set up a feed and bleed ratio where I dont have to do all that. I am also going to go get one of those 800 BTU heaters instead of the 1500 I have now.
  4. Aaron385

    Aaron385 Registered

    Also, on the HID topic, does having a digital ballast make any difference on the HID's? I know what the resellers sites say.. Im interested in personal expierence.

    I have a 150W (Actual watts) 10,000 lumes huge CFL on the plants now and a few more moderate sized CFL's as well. I am using this setup to test my theory so I have my method down when I get a 600 -1000 watt setup for another 4x4x8 closet that will be available as soon as I get rid of that pesky washer and drier that is in it now. Who needs a W/D when you could be growing pot.. I mean vegitables.. in a perfectly good and already hooked up with H20, Drain lines, Outside Vent and 240V room! The laundromat is in my future :)
  5. Aaron385

    Aaron385 Registered

    I have determined a simple and easy way to hook up a timer, a solenoid valve for the propane, and a readily available ignitor (like ones used on gas stoves) to make this a fully automated device with a construction cost under $100 and safer to operate than a gas powered cloths drier.

    This system would provide adaquate CO2 levels to a small to moderate area for months and months and when empty would only require a propane bottle switch out (much more common and much cheaper than CO2 bottle).

    Is anyone interested in this information or am I wasting my time posting it?
  6. smokesalot

    smokesalot Registered

    no please go on i love this shit you are way over my head and a verry intelligent person with alot of knowledage please post it i'm reading it and im sure other people are to and this is a new post sometimes it takes a day or so i'm sure someone in these boards has enough smarts to keep up with you they just havent found ya yet

  7. Aaron385

    Aaron385 Registered

    Thats cool, I need the motivation to finish this project or it will become a pile of scrap in the closet like all the others.

    Fun fact, 1 gallon of liquid propane makes 27,000 cubic feet of vapor, of which a catalitic heater can turn 5.25% into CO2. So that is 1,417.5 cubic feet of CO2 potential production per gallon of propane.


    1 ~ $13 Bottle CO2 (20lb) = 180 cuft CO2
    1 ~ $15 Bottle Propane (5 gal) = 7087 cuft CO2
  8. Jdog7000

    Jdog7000 Registered+

    Keep it up. I like this.
    Personally I would just buy a propane burning co2 generator for 500 bucks.
  9. knna

    knna Registered+

    Keep it. It seems a very nice setup. I live in a hot country (Spain), so i must avoid heaters, but i think it can be a good option for northern growers.
  10. Aaron385

    Aaron385 Registered

    I’m telling you guys, 800 BTU's is NOTHING.. The cheapest air conditioner Wal-Mart sells is like 5000 BTU's.. A catalyst heater is not very efficient at generating heat but due to the catalytic process (vice combustion) it generates far more CO2 than just burning the gas.

    Also remember that with CO2 you should be upping the grow room temp to 85F or so.. Which is probably more than the heater could do even if you wanted it to! I keep my grow'n room at 77F and when I shut the door to the closet and fire up my 1500BTU burner with no vent fan going it only gets up to the low to mid eighties. It gets to the same temp it would without the burner going (due to the lights) if I just shut the door to the closet.

    It really sounds like nobody has ever heard of this before. I checked with most of the major burner companies and they are all using open flame.

    I just checked the tracking on my atmospheric analyzer, its half way here. I am really just guess dosing right now, running burner for 10-15 minutes every four hours. Plant growth has responded quite nicely but I’m sure there could be other factors. Since I have been dosing over the last couple days plant growth has at least doubled (I keep having to move the lights). It could be other factors.. However, I hope when I get the analyzer in I can prove it isn’t.

    I will continue on and take pictures of the setup when I can find a digital camera to borrow. I expect to have some relatively conclusive data in the next week or two.
  11. Aaron385

    Aaron385 Registered

    Another thought is reducing the catalyst size even further to a size that only maintaing 1500ppm. For instance:

    If 3000 BTU maintains 34,000ppm @ 1 air exchange per hr then it would only take 132 BTU to maintain 1500ppm CO2.

    At 21,591 BTU/lb in propane a 15lb propane bottle last 200 days maintaining a grow room of moderate size at 1500ppm!

    Should this thread be moved to the advanced growing section?
  12. Jdog7000

    Jdog7000 Registered+

    My window ac unit is 8000btu's.
  13. Zandor

    Zandor Registered+

    Well I will sit back and watch and see how it goes then.

    You are making assumptions but time will tell. CFL do not produce enough light for the plant to absorbed the extra amount of CO² in the air. I have been growing with CO² for many, many years and I do have quite a lot of experience growing as well both with and with out enhanced CO².

    Only a blue flame will produce the desired CO². A red, green or even yellow flame will not produce measurable or usable CO² for growing.
  14. Aaron385

    Aaron385 Registered

    Zandor - First on the lights I will be using HPS (600-1000 watts depending on what comes across e-bay in the next couple of weeks). That should do the trick. Just trying to get my CO2 down now so it will be ready to go in a couple of weeks when it is really needed. The atmospheric meter arrived in my town today at 7am, yet still not delivered. Maybe Monday?

    Here is a clip from a science journal:

    In the process of catalysis, the contaminant gas enters the pores of the catalyst and it is there that it reacts with the active phase. Water, carbon dioxide and a halogenated compound are produced as a result of this reaction. This last product is subsequently neutralised in a shower of caustic soda. Thus, only H20 and CO2 are liberated into the atmosphere.

    - Note that this process is why you can put the heaters in your tent. Almost all VOC's are eliminated with the only tradeoff being higher CO2 levels but not anywhere close to toxic for humans. Even if the initial "burn" did not create the CO2, the catalist would reform VOC's into H20 and CO2.
  15. Aaron385

    Aaron385 Registered


    So DHL delivered my huge atmosphere meter this morning. I set it up and it was reading about 400ppm CO2.. I set the propane heater next to it and the readings went up to 2500ppm in a few seconds and then the meter displayed "O.R." (Out of Range maybe?). I shut off the heater and figured it was a good sign. Unfortunantly it never stopped reading "O.R." and I have reset it a bunch of times, taken it to a different part of the house and turned it on.. even took apart the case and vented it.. but no luck. I think the high level of CO2 fried the sensor. It is an obsolete model and the manufacturer does not make parts for it any more. Im going to give it another couple of hours before it hits the dumpster.

    Wish I had better news :(
  16. Zandor

    Zandor Registered+

    Sorry to hear about your bad luck.
  17. Aaron385

    Aaron385 Registered

    yea the meter never came back around.. its toast
  18. 4x5

    4x5 Registered+

    take the batteries out of it, put them back in, have you tried that?
  19. busteruk7

    busteruk7 Registered+

    sounds interesting
    cheers all :)
  20. Aaron385

    Aaron385 Registered

    got a new meter but it still needs to be cal'd.. it came out of the box reading outside air at 1000ppm.. i cal'd it at 400ppm outside then brought it in for some fun..

    i tried dry ice first and it brought the room up nice.. then the burner.. which was nowhere close to a lb of dry ice sublimating under an hps light but it did work.. will be more specific when i get this meter actually calibrated with some real cal gas.

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