Tankless Water Heater to Make CO2... WITHOUT WASTING WATER

[brown_thumb]

If I use a propane tankless (on demand) water heater to add CO2 to my grow, I'll need to recycle the water. My home is all electric but I could run a small heater on a propane tank. Is it feasible to use a high-volume water pump to feed the heater from a cattle water tank with the heated water recirculated back to the tank? Evaporation could keep the water cool enough and it could be outside the grow room/greenhouse... outdoors. A float valve could be added to keep the tank full. Of course a water treatment regimen would be needed to prevent algae growth, mosquito larvae, etc. The goal is to add CO2 without overheating the grow room.

 

[DemonTrich]

How do you get co2 from an electric h20 heater? You need propane to get co2 by product.

 

[brown_thumb]

Ha ha... sorry. I left out important information. Original post edited.

 

[DemonTrich]

Thought thankless were electric not gas operated.

Just checked HD. They make them min LP.

 

[brown_thumb]

Right, thank you.

Any idea if the cattle watering tank (a small one) with a high-volume pump would suffice to cool the water via evaporation so I can run the tankless heater in the grow room without having to run hot water out into the yard?

BTW, I guess I'd have to add a filter to avoid circulating debris into the water heater. A cover over the animal watering tank made with metal or vinyl screen would keep large debris out.

 

[JJ Lowe]

Make sure you get a high powered pump. I upgraded pumps 3 times before finding one that worked.. I ended up scrapping it and going with a regular 4 burner..

 

[brown_thumb]

JJ, you've already tried this?

 

[Can of Bliss]

If you have an estimate for the most co2 you would ever need in an hour the math can be done.

I would guess that a water heater has a much bigger burner than you would want i.e. it would only need to be on for a few seconds to get the co2 you want.

 

[brown_thumb]

CoB, are you saying that if I get the size of CO2 generator right, the heat is not an issue? Summer ambient temperature often reaches 105 F here.

 

[coldcanna]

I guess my first question for you here is.... an actual co2 tank and regulator isnt any more expensive that a heater so why not just buy the correct equipment?

 

[brown_thumb]

I guess my first question for you here is.... an actual co2 tank and regulator isnt any more expensive that a heater so why not just buy the correct equipment?

That's a good point. I live in a rural area near a small town. I can easily purchase propane here but exchanging a CO2 tank will take a 2-3 hour round trip. I suppose it depends on how often I'd need to do that. I'm often not able to drive that far. Also, I can't physically handle very large tanks anymore.

 

[Can of Bliss]

CoB, are you saying that if I get the size of CO2 generator right, the heat is not an issue? Summer ambient temperature often reaches 105 F here.

No, just that a water heater may preform really poorly as a co2 generator.

Do you have any estimate of your co2 needs? What is through cubic feet of the grow room, how well sealed? What is the max/min wattage being run. Do you have a chosen water heater model, or would you like me to do that math with a cheap one from a big box store's website?

 

[brown_thumb]

My CO2 needs will vary. Currently, I have 15 plants that average 8 inches tall. But... they will grow. Later, I may raise 30 plants. I'll have to enlarge my current grow space to accommodate the current crop as it grows. So multiple smaller CO2 generators may make sense.

Because my needs will vary, the size of the grow area will vary. Currently the 15 small plants are in an approximately 30 ft3 of space and it's very poorly sealed but that will soon expand to accommodate growth of the current crop. I will probably move my grow inside but that's in the future... likely this spring (approximately 3 months). Then I'll be growing in a space approximately 8x12x8 feet (approximately 768 ft3) and that space will be fairly well sealed. But again... that's months in the future.

 

[Lazyman]

Both of those grows are too small for a CO2 generator, the hot water output from them is at 150* and would have your cattle tank steaming in hours. Bottled CO2 is by far your best bet. Welding supply companies sell it cheaper.

 

[brown_thumb]

Okay but where do I buy CO2 in my little town? I live in a rural area and San Antonio, TX is a 2-3 hour round trip for me not counting the business stop.

 

[Lazyman]

Welding supply places are plentiful, use Yelp.com to find one near you. That small of a room I'd use small tanks anyway.

 

[Can of Bliss]

http://m.homedepot.com/p/MAREY-2-0-...obileweb_pip_rr-2-_-204357327-_-203378689-_-N


About 34,600 btu

Propane gives off 21,600 BTUs per pound,
So 1.6 lbs and hour running
Probably don't want to burn it for less than a minute. They don't start up instantly, and burn it a little shitty at first.
So for one minute, about 0.43oz of propane burned.

C3H8 + 5O2 = 3 CO2 & 4H2O

26 + 80 = 66 + 40

So you get 66/26 * 0.43= 1.1 Oz of CO2 per minute of burn time.

A cubic foot of air is roughly 1.3 oz.

So to rase from 400 ppm to 1400ppm would require 0.0013 oz of CO2

So 1.1oz/0.0013= 846 cubic feet.

I would say it could work, it would be crude and co2 levels would have to swing between cycles. I am not concerned with the few gallons Iof water cooling down.

In practice this will be more complicated and experience to set up than something designed for growing.
Also, I feel that most people jump to co2 too soon. There are lots of ways to boost yield that are less expensive. If you do have everything already tuned it perfectly, it's a good step to turn everything up to 11. But if somethings are only getting turned up to 5, co2 isn't going to help much.

 

[Can of Bliss]

Oh, I messed that up a bit and I need a few more posts in order to edit.
Anyway, the math about the reaction formula is all wrong, but it's not like it's off by an order of magnitude.

 

[brown_thumb]

Welding supply places are plentiful, use Yelp.com to find one near you. That small of a room I'd use small tanks anyway.

Excellent... I found ONE place in my little town that sells tanks and refills. I'm surprised and happy I found it. Their prices seem reasonable too. Thank you for suggesting yelp.com.

I assume you're recommending a 5 pound tank rather than 10 or 20 pound? I'll probably be assembling a larger box to accommodate 15 five gallon buckets. The size of the new enclosure will be approximately 4x8x8 or 256 ft2 (7250 liters) but it will be better sealed than the current enclosure.

 

[HazyBulldog]

main question..... why


Never mind, already answered.