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Cannaversity .: Cannabis Cultivation .: Ventilation & Odour Control .: Cheapo Micro CO2 System

Cheapo Micro CO2 System

  Safety Warning


   Be aware that with fire extinguishers:

  • The gas will be at pressures between 700 and 2200PSI
  • The valve opens quickly and has a very high flow rate
  • CO2 is stored as a liquid that evaporates at -78degC and will cause frostbite burns as well


Required Parts

  • CO2 type fire extinguisher
  • CO2 regulator
  • Plumbing adapters
  • Irrigation valve
  • Telaire CO2 meter
  • Display for Telaire Meter ( optional but HIGHLY reccomended )

Everyone would like a CO2 system but the equipment is a little expensive… One of the most expensive parts is the cylinder, which to rent will cost about $150/year and to buy new will cost around $300. Then you also require a pressure regulator, a solenoid valve and (depending on the type of controller you have) possibly a flowmeter.

Fortunately our hobby shares a lot of this equipment in common with home beer brewers. This is a popular hobby in Australia, making CO2 pressure regulators cheap and easy to buy. Also, in a scientific discovery nearly as significant as electricity or the atom, home brewers have discovered that CO2 type fire extinguishers can be used as CO2 bottles!!!

My own investigations have discovered that a $20 irrigation valve from Bunnings can be used as the solenoid valve. I can’t think how to make a flowmeter with parts from Bunnings, so instead I will demonstrate how to use a Telaire 800x CO2 monitor as the controller.

CO2 bottle

What can you use for a CO2 bottle? You can’t use an LPG bottle, or air-compressor cylinder. You need a proper high-pressure gas cylinder.

Renting a cylinder

Here is what you are looking at to rent a bottle from BOC or Air Liquide (Sydney prices).

IPB Image

In Victoria I’ve heard you might be able to rent a steel CO2 bottle for $15/year from one of the suppliers. Also notice that larger cylinders are much better value for money, and you will use a lot of CO2 if you are growing with it.

Another consideration to keep in mind is that suppliers will only refill/swap their own bottles so that has to be a large factor in choice if you choose to go that way .

Buying a cylinder

You can buy your own new cylinder from a place like They charge $300 for the bottle, so after 2.5 years it will be cheaper than renting. You can also sell it 2nd hand if you change your mind. A refill involves taking the bottle to one of their distributors to be swapped; you will pay about $6.50/kg for a refill. You also need to do a pressure test every 10 years for $40.

Again though suppliers will only refill/swap their own bottles so that also has to be kept in mind.

CO2 Type Fire Extinguishers

A CO2 fire extinguisher (FE) is exactly the same type of bottle, except it has a different type of valve and a dipstick to dispense liquid rather than gas. FE’s come in 2, 3.5 and 5kg sizes. A new CO2 fire extinguisher will about $300, but you can get them for $50 2nd hand. They cost about $10/kg to refill and need to be pressure tested every 6 years at a cost of $40. The date stamp on the top of the cylinder shows the time it was tested. Call around for refill prices, the lowest price I got to refill a 3.5kg was $37 and the highest was $104.

Summary: a FE is like a rent-free bottle although they may be more pricey to refill.

What do you need to do to use an FE as a bottle?

The major problem is the outlet thread. Because it will not be connected to a regulator, manufacturers might use a different thread on every model of FE.

The thread we need is male ‘Type 30’, this is what is used in Australia for CO2. A CO2 regulator will have the female version of this thread on the inlet.

IPB Image

Unfortunately there is no easy way to know if your extinguisher has this until you’ve bought it. I’m feeling pretty smug because I bought two 3.5kg Wormald brand extinguishers that only needed to be drilled out with a 1/2” bit to make them Type 30 compatible.




This drilling out was needed so I could mate up with the Type 30 on my regulator, which has a ‘spigot’ (a bit that extends out from the face of the seal). I made sure to jam the valve while drilling it so that I didn’t get a face full of CO2.

This is a bit dangerous because I’ve modified a part that will be under pressure. Also, a refiller might refuse to refill it now.

This is what the female part on the regulator looks like (showing the spigot, some CO2 regulators don’t have the spigot).


I’m also showing some seals I found at Bunnings that seem to work. However you should really go to a home brew or hydro shop and get a proper seal.

Some extinguishers can be used without modification, some need a little change like this, some need a lot. I also bought a Chubb brand extinguisher that has a completely different female thread, so it would need an adaptor.

This some related info I got from home brewer forums that might be relevant if using a FE as a bottle:

Wrong thread?

* Get a nice refiller to replace valve with Type 30 tap
* Get a ‘Turner and Fitter’ to make an adaptor (for about $50?)

Is it enough gas?
FE’s come in 2, 3.5 and 5kg sizes. I don’t have a lot of experience growing with CO2 but from reading other peoples experiences I get the impression that 5kg might only last 1-2 weeks. Of course it completely depends on your grow.

Home brewers use much less gas than we do, so you may look suspicious if you get a lot of refills. Perhaps alternate between suppliers and/or claim your keg is leaking?

Leaking Valve
There are 2 seals in the valve, the smaller one can leak because it is only designed to hold pressure for the 30s it takes to spray the extinguisher. I don’t think this will be a problem at the rate growers use gas. Mine does not seem to leak.
* Try rotating the valve stem to clean it (but be careful to release pressure in the regulator if you do this. The lever may be holding the pin in place and for one person the pin broke half way and the pressure shot it out)
* Replace the valve (preferably with a tap)

The dipstick makes the FE dispense liquid CO2 which will de-pressurize in your regulator rather than your bottle, causing the regulator to get very cold and maybe even damage it. * Tip the extinguisher upside down to get gas, or
* Ask re-filler to remove the dipstick when they do a pressure test or refill

This is what happens if you don’t remove the dipstick or turn it upside down:


Can you substitute something for the regulator? No, you can’t use an LPG regulator or an air-compressor regulator.

I am pretty sure it is OK to use a regulator designed for nitrogen, argon, helium etc. If the gauge goes up to 4000PSI, it should be OK. I don’t think there are any other issues like there are for oxygen which is very reactive.

Fortunately CO2 regulators are cheap because they are used in home beer brewing and you can get them for about $75 on ebay.

Solenoid Valve

The solenoid valve controls the dosing of CO2 into your room. The valve has to be able to cope with your outlet pressure from your regulator (up to about 60PSI), and be suitable for use with CO2.

Normally when you buy a CO2 injection kit you will get a high quality industrial grade solenoid valve.

I’m using an irrigation valve because they are about $20 at Bunnings. An irrigation solenoid valve will be rated for 150PSI inlet pressure and 24VAC operation (but I am using 7VDC with no problems). I’m not sure if they are suitable for CO2 but it’s working so far.


This one has a 1” BSP female connection on the inlet and outlet. It has a manual override which can leak; if I did this again I would use another type that Bunnings sell with no manual override or flow control. Don’t just buy the cheapest valve they sell, buy the one with no manual override or flow control.

Connecting it all together

A home brewing regulator will have an outlet barb for 6mm beer line, you will probably be able to unscrew it and then you will have a ¼” BSP female outlet. That is my experience anyway. The outlet pressure will be adjustable and probably under 60PSI.

Originally, to connect the regulator to the valve, I tried to keep the barb on the regulator and then use irrigation tubing and fittings to connect to the 1” valve inlet. This was easy but I could not stop it leaking and gave up.

So I went to a plumbing supply store and they gave me two brass fittings that did the job much more solidly and compactly for about the same money.

This photo shows how they fit together, including the tubing I tried to use.

I think the brass fitting on the left is called a reducing bush, and the one on the right is called a reducing nipple.

This is what it looks like when assembled:

I had to use a lot of thread sealing tape, especially on the ¼” outlet of the regulator. I think it is designed for a fitting with ‘tapered threads’ but I am using a common ‘parallel thread’ type fitting.

Note that the valve has direction of flow marks, this is important.

Note I also used a 1” plug on the outlet of the valve. This is not actually plugging it, it is to significantly reduce the flow rate, otherwise it flows too fast.


Now you have a CO2 delivery system and you need a controller.

The type of controller you need depends on whether you have a flowmeter. The two types of controllers are:
1. Timed Injection (a term that I just made up)
2. CO2 meter

A timed injection controller (such as a Compugas) uses a flowmeter and a timer to inject the right amount of gas into your room. These controllers are cheaper but inaccurate.

A CO2 meter does not need a flowmeter because they measure CO2 level directly. These are accurate but more expensive.

Control with a Telaire CO2 meter

Because the setup I have shown does not have a flowmeter, it will need a CO2 meter to control it.

Lots of growers are using common (at least on US ebay they are common) Telaire 8001 meters. These have a relay output that by default will activate below 1000ppm.

To use it, all you need to do is supply the valve with power via the relay contacts.
IPB Image

One wire from your low voltage power supply goes straight to the valve. The other wire is switched by the relay. Connect one end to the ‘common’ contact and one to the ‘normally closed’ contact.

If you can figure out how to connect the valve via the relay, the Telaire will control your CO2 levels something like this:
IPB Image

It doesn’t take a lot of CO2 to raise the level from 350 (normal air level) to 1500ppm, so make sure you use a very low flow rate, otherwise you will get massive overshoot which could upset the plants. There is no way to know this unless you use data logging software like I am, so if in doubt, reduce the flow rate. I had to adjust the output down to a leak that you can barely hear, and that was in a room of 35m^3. There’s no disadvantage in having a very low flow rate.

Have fun!


  Safety Warning


   Be aware that with fire extinguishers:

  • The gas will be at pressures between 700 and 2200PSI
  • The valve opens quickly and has a very high flow rate
  • CO2 is stored as a liquid that evaporates at -78degC and will cause frostbite burns as well

author enn
editor: Pure

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