CO2 vs compressed air

CO2 vs Compressed Air

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One of the most commonly-asked questions in paintball (apart from “what is the best paintball marker?“) is “What is the difference between CO2 and compressed air tanks?” Or “Which is better – CO2 or compressed air?”.

Both HPA and CO2 are sources of the pressure that pushes the paintball out of the barrel; however, there are many differences between them. Depending on your marker, you may only be able to use one type.

What Is CO2?

When paintball first started, all paintball guns used CO2 as a propellant. CO2 is a gas at room temperature; however, when compressed & stored in a tank, it becomes liquid and must expand into gas to fire the paintball through the barrel. When liquid CO2 expands into a gaseous form, it creates pressure; this pressure is what shoots the paintball.

The reason why CO2 was initially used for paintball was because of its density – CO2 is much denser than compressed air. This is the reason CO2 tanks are only rated to 850 psi, while compressed air tanks are rated to either 3000 or 4500 psi – more air is needed to move the paintball at the required speed (280 fps). Therefore, a higher pressure tank is required to deliver the same number of shots. Paintball markers that use compressed air use a secondary regulator to drop the pressure down to the gun’s working pressure – CO2 does not need this.

CO2 is typically used for lower-end mechanical paintball markers, as CO2 can cause electronic components to wear prematurely. You should refer to the owner’s manual for your marker to check if it is CO2 compatible or requires the use of compressed air. If your marker uses a battery, it probably requires compressed air.

One issue with CO2; you can’t easily tell how much is left in the tank in-game – with HPA you can tell when you’re running out of air (using a pressure gauge), as the tank pressure will drop as the air runs out. As CO2 is liquid in the tank, the pressure will stay constant until all the liquid has gone. The weight of the CO2 in the tank will decrease as it runs out, but the effect is not significant enough to notice without removing and weighing the tank – obviously not ideal if you’re under heavy fire in the middle of a game!

Whether you use CO2 or HPA doesn’t affect your hopper; so if you have an electric hopper, it will not be affected by which air system you choose.

Types Of CO2 Tanks

There are two types of CO2 containers commonly used in paintball: 12-gram disposable (non-refillable) CO2 cartridges and refillable CO2 tanks or cylinders.

Disposable cartridges are typically used in low-end markers and pistols.

Refillable CO2 tanks are made of aluminum & are filled until they reach a prescribed weight (rather than a cut-off pressure). CO2 containers are available in various sizes, typically 9, 12, 16, 20, and 24oz (20oz being the most common size). The numerical values of a refillable CO2 tank tell you the liquid capacity of the tank (as the CO2 inside will be liquid). A 20oz tank offers a good balance between capacity and size/weight of the tank for most situations.

Pros Of CO2

  • Low cost (initial and ongoing)
  • Smaller & lighter than HPA for the same number of shots
  • Easier to find refilling facilities away from the field (typically gas stores & welding suppliers, as well as paintball stores, carry CO2)
  • Works well with lower-end markers, suitable for beginners

Cons Of CO2

  • CO2 becomes very cold when it expands to a gas
  • Liquid CO2 can escape into the marker, causing problems
  • Inconsistent performance, particularly on cold days
  • CO2 tanks can’t be partially refilled, so no in-game top-ups
  • Can damage electronic components and marker seals
  • No reliable in-game way to tell how much CO2 is left in the tank

What Is Compressed Air (or HPA)?

To avoid some of the drawbacks of CO2, manufacturers began experimenting with compressed air (also known as High Pressure Air or HPA).

Compressed air is simply air from the atmosphere, compressed & forced into a container. The more the air is compressed, the more air can fit inside the container.

HPA tanks are pressurized up to the tank rating of 3000 psi or 4500 psi. The pressure then drops through a regulator, down to the marker’s working pressure of either 850 psi or 450 psi (some markers need the lower pressure). HPA remains in its gaseous state when compressed, avoiding many of the issues related to gas/liquid phase change.

Types Of Compressed Air Tanks

Compressed air tanks are available in two types: aluminum and fiber-wrapped.

  • HPA aluminum tanks are rated up to 3000 psi. They are smaller and cheaper but weigh much more than fiber-wrapped tanks.
  • Fiber-wrapped tanks are rated from 3000 psi to 4500 psi (depending on model), cost more and have more volume, but are much lighter than aluminum tanks.

Tanks are available in several sizes, as well as the two pressure rating mentioned above. Note that 3000 PSI or 4500 PSI are the pressure the tanks can withstand, not the pressure of the air coming into the marker; 4500 PSI will give you more shots than 3000 PSI in the same tank size.

Compressed air tanks are described by their manufacturers as a size and a rating: for example, if the tank rating is 13/3000, that means 13 cubic inches (ci), and safe to fill up to 3000 psi. The rule of thumb is you’ll get about ten shots per ci at 3000 psi, and 15 shots per ci at 4500 psi (high-end markers are usually a bit more efficient than this). Available compressed air tanks range from 13/3000 to 100/4500, in various lengths and shapes. 3000 psi tanks are usually aluminum, while 4500 psi tanks typically have a supporting carbon fiber wrap.

Pros Of Compressed Air

  • Consistent pressure – rapid firing or cold weather barely make a difference
  • Can be filled at the field between games
  • No risk of liquid leaking into the marker
  • Less damaging to marker seals & components
  • Required by most high-end or electro-pneumatic markers
  • You can check how much air you have left using a pressure gauge

Cons Of Compressed Air

  • More expensive to buy initially
  • Tanks are larger and heavier than CO2 for the same number of shots
  • Harder to get refilled away from a paintball field (3000psi is too high for domestic or tire shop compressors)

Which Is Best?

In the long run, HPA is probably the best investment, as it is easier on the gun interior and offers smoother performance. The advantages over CO2 in being able to play in any weather and with any firing frequency pay for themselves. Also, an HPA tank is an investment that can be transferred to any marker you upgrade to if you decide to swap your entry-level marker for a better performer. Note that some markers required compressed air – in general, most electronic paintball guns should use compressed air, and most mechanical guns can use either HPA or CO2.

If you’re just dipping your toes into the world of paintball or are short on cash, you don’t need to invest as much money if you start with a CO2 system. For beginners, CO2 works very well, and most beginners won’t notice the difference between CO2 and compressed air in an entry-level marker. If you decide paintball will become a passion upgrade to a higher-end marker, you will likely need to switch to compressed air at that stage.

Frequently Asked Questions (FAQ)

Can you fill a CO2 tank with compressed air?

Theoretically, you could, however, in practice, it’s not recommended. CO2 tanks are rated to a much lower pressure than compressed air tanks. If you fill a CO2 tank with HPA to the CO2 tank’s limit of 850psi, you won’t even have 1 hopper’s worth of propellant. If you attempt to fill a C02 tank to the 3000psi or 4500 psi HPA tanks are filled to, you will likely have a sizeable accident involving shrapnel flying in all directions at high speed. Don’t even try this…

Am I allowed to fill my tank without assistance?

All air tanks, regardless of the type of system, must be shipped empty (except 12-gram cartridges, which must be transported by land).

CO2 tanks can only be filled by a qualified operator. The larger liquid CO2 tanks used to refill your tank are dangerous if mishandled. Also, it’s essential to empty your CO2 tank before refilling. Your CO2 tanks will be weighed before and after, to measure the amount a CO2 tank has been filled.

Filling a compressed air tank at the paintball field is quite safe and straightforward – just make sure the filling station you use is the correct one for your tank rating (3000 psi or 4500 psi). If you’re not sure what to do, just ask at the field, there will always be someone to help.


Never fill a 3000psi compressed air tank above 3000 psi. Be sure to use the appropriate filling station when filling a 3000psi tank.

4500psi can be filled at the 3000 psi filling station, but the tank will not be fully pressurized.

All tanks must be regularly tested (check the hydro date stamped or printed on your tank). Most tanks need to be tested every five years, costing around $20-$40; some cheaper tanks need to be tested every three years.

There are some markers with RT (Response Trigger), which need the slightly higher working pressure of CO2 for the RT to work correctly. There are HPA tanks available with slightly higher (or adjustable) outlet pressure; one of these should work just fine if you’ve slapped an HPA tank on your marker and found your RT suddenly doesn’t work.

A CO2 tank must be completely empty before filling, and must be removed from the marker to be filled. A compressed air tank can be filled while fitted to the marker, and don’t have to be emptied first, allowing you to do a quick top-up between games.

Domestic or tire shop air compressors can’t deliver air at a high enough pressure to fill a 3000psi, or 4500 psi compressed air tank (typically they top out around 180psi). One popular way to get around this limitation is to use a scuba tank. You can buy a scuba tank adaptor for this purpose.

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