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The Complete Beginner's Completely Incomplete Guide to Oxygen Not Included



  • Introduction & background

  • SPOM basics

  • Dealing with heat

  • Choosing a SPOM: how much oxygen do you need?

  • Where to build your SPOM

  • A closer look at the (smaller) SPOM

  • IMPORTANT: include an overflow for excess hydrogen

  • Firing up your SPOM: gas management and initial power

  • SPOM in the wild: Example SPOM, water geyser, and Anti Entropy Thermo-Nullifier



The Original SPOM (MK II)

There are a few key moments in any Oxygen Not Included gamer's life. Moments that will forever change how you play the game. One such moment is likely to be when you build your first SPOM.

A SPOM turns water into oxygen - and generates enough power in the process that it can power itself. Once built, all you have to do is supply your SPOM with water and it will keep producing oxygen - and powering itself - forever.

SPOM stands for "Self-Powering Oxygen Module." The idea was first presented in two 2018 posts on Klei's forums by QuQuasar (SPOM version 1, SPOM version 2). Changes in game mechanics mean those original designs no longer work as intended, but the SPOM lives on.





Hydrogen Generator


Electrolyzer output. This electrolyzer was started in a vacuum. It filled the room with roughly one tenth hydrogen and nine tenths oxygen. Hydrogen rises above oxygen.

There are several machines in Oxygen Not Include that produce oxygen. You are probably familiar with at least the Oxygen Diffuser, which consumes algae and produces oxygen. The SPOM uses a machine called an Electrolyzer.

Electrolyzer basics

  • It consumes Water and produces two gases: Oxygen and Hydrogen

  • It produces roughly 90% oxygen and 10% hydrogen (the exact numbers are 888g/s oxygen and 112g/s hydrogen.)

  • It has a liquid intake for water

  • There is no gas output piping: oxygen and hydrogen are released into the surrounding area

  • The heat of the gases it produces depends on the heat of the water you input: it will be as hot as your input water, but will be at minimum 70C

  • It requires power (120 W)

To become self-powering, the SPOM uses a second machine: the Hydrogen Generator. A hydrogen generator consumes hydrogen and produces power (and heat).

Gases differ in weight; hydrogen is lighter than oxygen. The hydrogen an electrolyzer produces will work its way up above the oxygen. The SPOM uses this gas mechanic to its advantage by placing gas pumps higher up and lower down, for hydrogen and oxygen respectively.

The basic idea behind the SPOM is to separate the gases produced by the electrolyzer:

  • the Oxygen is pumped into your base

  • the Hydrogen is pumped to a hydrogen generator

The hydrogen generated by a SPOM's electrolyzers is more than enough to power the SPOM - it will even produce excess hydrogen.

There are many possible uses for the excess hydrogen. One option is to use it for easy(ish) cooling by piping it to an Anti Entropy Thermo-Nullifier.

While on the topic of cooling - we need to talk about heat.



Anti Entropy Thermo-Nullifier (AETN)


Thermo Aquatuner


Steam Turbine

The electrolyzer produces oxygen that is +70C (or hotter). The good news is that it will take a very long time for your SPOM to actually heat up your base to those temperatures. The bad news is that it will nonetheless constantly add heat to your base.

In theory you could run a Vault-Tec inspired experiment where you see how well a colony of dupes fare as their base creeps towards boiling point. If that doesn't sound like your cup of tea, you'll need some kind of cooling.

There are two main options regarding SPOMs and cooling:

  1. Cool down the oxygen before it enters your base.

  2. Pump hot oxygen into your base and instead run a cooling loop through your base.

(If I have a small colony, I usually use a combination of the two: I have a cooling loop that runs through my base and that also passes through my SPOM, cooling both.)

Building a SPOM isn't that difficult, the challenge tends to be cooling. Or, more specifically, getting your hands on the materials needed for cooling builds. Specifically, plastic and/or steel.


Here are three alternatives for cooling, presented in increasing order of difficulty.

1. An easy albeit temporary approach to cooling is running the oxygen gas pipes from your SPOM through an ice biome. This will cool down the oxygen in the pipes. (Use radiant pipes for improved temperature transfer between the oxygen and the ice biome.)

Some downsides to this approach are that you will slowly start to heat up the ice biome, and that it is difficult to control the temperature oxygen enters the base at.

2. If you are on a map with ice biomes then you might also have an Anti Entropy Thermo-Nullifier on your asteroid. These provide a stable, controllable, long-term solution to your cooling.

3. A third, and incredibly powerful approach to cooling is a cooling loop that uses a combination of a Thermo Aquatuner to cool down the liquid in the loop and a Steam Turbine to burn off (or turn into power) some of the heat generated by the thermo aquatuner.

This is the end-game cooling build that, as long as you have enough power, can solve all your heat problems, regardless of what asteroid you're on. However, it requires both plastic and steel.


Pictures and overlays for cooling options 2 and 3 above are included on this site. I also cover them both more in-depth later in the guide. Links:

To reiterate a point from earlier: if your base is a "normal" temperature, it will take a long time for your SPOM to heat it up significantly. It will take a long time even for the area inside the SPOM to heat up to +75C, the point where (non-gold) machines will take damage.


I have postponed implementing SPOM cooling somtimes by hundreds of cycles and have yet to have it overheat. So, while you will want to implement cooling at some point, you don't need to have it ready as soon as you fire up your SPOM. (As pretty much any dupe will tell you: if you're running out of algae, hot oxygen is better than no oxygen.)



Neural Vacillator

You can build SPOMs of various sizes. This site has build guides for two SPOMs: a small one (oxygen: 1kg/s) and a large one (oxygen: 3kg/s). Which to choose mainly depends on how many dupes you want to be able to support.

Dupe oxygen consumption:

A standard dupe consumes 100g/s of oxygen. This can be affected by positive and negative traits.

  • Dupes with the Mouth Breather trait consume +100g/s of oxygen

  • Dupes with the Diver's Lungs trait consume -25g/s of oxygen

  • Dupes with the Deep Diver's Lungs trait consume -50g/s of oxygen (this trait can only be acquired using a Neural Vacillator)

The small SPOM produces 1kg/s of oxygen. In theory that is enough for 10 standard dupes. However, it's a good idea to have a bit of extra oxygen production - you want enough extra to fill your base and any Atmo Suits with oxygen.


Some rocketry and space exploration-related things also require oxygen. But you don't need to consider space stuff now if that feels overwhelming - you can just build another SPOM later if needed.

So a rough rule of thumb is:

  • If you have fewer than 10 dupes (with standard oxygen consumption) then the smaller SPOM should do. (But, to have a bit of a safety margin, I'd say 8 or fewer.)

  • If you want to support 10 or more dupes (with standard oxygen consumption), you either need a larger SPOM or several smaller ones.

On Neural vacillators and the Neural Vacillator lottery:

Neural vacillators give one trait per use, then they have to be recharged. (Charges are found in space. I'll cover that later.)


There are four possible traits a neural vacillator can give; Deep Diver's Lungs is one of them. Meaning you have a 25% chance to get it.

A dupe can have all four traits a Neural Vacillator gives, and can only get each trait once. So if you keep putting a dupe in a neural vacillator, you will eventually get Deep Diver's Lungs. (On your fourth try at the latest.)

You can see what traits a dupe has by clicking on them and selecting "Bio." But you don't need to be too careful: if a dupe that has all four traits uses a neural vacillator, nothing happens. The charge isn't used.


When deciding where to build your SPOM, it's worth considering at least water and cooling.


Your SPOM needs a steady supply of water. So one option for placement is near a water geyser of some kind. This is particularly relevant if you will use hot water. Having your SPOM close will mean you won't have to pipe hot water long distances. (Regardless, remember to use insulated liquid pipes to minimize heat spread.)


How will you cool the oxygen? (Or your base, if you aren't cooling the oxygen.) If you will be using an Anti Entropy Thermo-Nullifier to cool the oxygen, building your SPOM near the AETN will minimize the distance you will have to pump hot oxygen for cooling.

Now let's have a look at a SPOM.


We'll start with the machines in the electrolyzer room, where the oxygen and hydrogen are produced.

This SPOM uses two electrolyzers. There are gas pumps on slightly different heights - the upper pump is for hydrogen, the lower two are for oxygen.


Gold Amalgam. Found wherever there is slimelung, polluted water, and other yuckiness.

The doors on either side of the hydrogen pump (the pump in the middle) are to keep oxygen from getting to the hydrogen pump. The doors can be replaced with walls if you prefer, but doors are convenient for access when building or repairing.

The mesh tiles under the electrolyzers help with gas flow. You could use airflow tiles there instead, but a benefit of mesh tiles is that any accidental liquid drops will fall through. (A drop of liquid in a SPOM can be hard to detect, but mess with the SPOM's functioning.)

The way the build works is that hydrogen emitted by the electrolyzers rises above the doors and is pumped by the gas pump in the middle. Oxygen sinks down below the hydrogen and is pumped by the gas pumps on the sides. The room shape helps with keeping oxygen and hydrogen separated.

(The final design also has Atmo Sensors for each pump, to help keep the gases separated by controlling when the gas pumps kick in.)

The tiles are Insulated Tiles to keep heat from the SPOM from seeping into the surrounding area. To avoid damage to the machines from overheating:

  • Use gold amalgam to build the machines in this area

Gold can be found in the slime biome. Some asteroids, like the Badlands, don't have slime biomes and so don't have gold. (Note: the world trait Geodes can add gold.)

If gold isn't an option you can build machines out of steel. Or run cooling through the SPOM, in which case you can build the machines out of any material. (And don't have to bother with the insulated tiles, ether.)

And now for the upper floor - the power-related stuff. The basic idea is: turn hydrogen into power for the SPOM. There are different ways to build this section. Here's a standard approach.


Atmo Sensor

The upper layer, from right to left, has:

  • a tank to store some extra hydrogen

  • a hydrogen generator to convert hydrogen into power

  • a smart battery to store that power

  • a power transformer that is then connected to the machines in the lower layer. (If you don't connect anything else to this power grid then you can get by with a small power transformer.)


In addition to this, the SPOM has Atmo Sensors (not included in the pics above) connected to the gas pumps. They keep the balance between oxygen and hydrogen, and make sure the SPOM's gas levels don't get too low. And, finally, there is a whole mess of wiring, piping, etc. (Also not included in the pics above.)

Keep in mind that the machines on the upper layer also generate heat. And a Gas Reservoir full of hot hydrogen can also let off heat. One solution is to enclose the area. Another option, and what I do, is to run cooling through the area. (Cooling loops are covered later in the guide.)



Overflow mechanism. Both versions accomplish the same thing. Gas (flowing from right to left) first tries to cross the gas bridge. If it can't, it flows along the gas pipe upward.

SPOMs produce more hydrogen than the hydrogen generator(s) need. Which means you need an overflow mechanism to get rid of excess hydrogen.

Over the years, whenever something has gone wrong with my SPOM, it has usually been because I had built the SPOM and then decided I'd get around to building the overflow mechanism "in a bit," once I was done with some other things that needed doing.


And then, later - after I completely forgot about building the hydrogen overflow mechanism - I wonder why my Atmo Suit docks are getting damaged. (One side-effect of a clogged hydrogen pump is the gases get mixed and you can end up with hydrogen in your oxygen gas pipes.)

What you do with your excess hydrogen is your business - just make sure you do something with it. Some options:

  • Pump it into Gas Reservoirs for later use. (End-game rockets can burn liquid hydrogen.) Note that you will need to keep adding more (and more and more) reservoirs, so keep an eye on them.

  • Send hydrogen to a Canister Filler, so you have access to hydrogen canisters when needed. (E.g. to add to a Drecko farm to enable scale growth.)

  • Pump excess hydrogen to a hydrogen generator for extra power. Note: don't automate that hydrogen generator to stop when batteries are full, as that will lead to your hydrogen clogging up.

  • Use excess hydrogen to power an Anti Entropy Thermo-Nullifier (or several). Note: AETNs don't use that much hydrogen, so you will need to have an overflow mechanism for that as well.

  • Vent it into space.

  • Any combination of the above

The gas pipe overflow mechanism is the same as for water. Have your main hydrogen line go along a Gas Bridge and your overflow pipe branch off from the Gas Bridge input pipe section. (For a refresher, see: Liquid overflow mechanism.)


SPOM gas piping example. ​The hydrogen first passes through a Gas Filter (set to hydrogen). Then it comes to a Gas Bridge, which means gas first tries to go left - to the Gas Reservoir and Hydrogen Generator. When full, gas overflow is split between the canister filler and the overflow pipe to the right.

I include a permanent hydrogen gas filter in all my SPOMs. Braver people than I leave out the gas filter. If nothing ever goes wrong with your SPOM, the gas filter is a waste of power. I tend to assume something might go wrong at some point (like the hydrogen clogging up or there being an interruption in the water supply), so I include the filter as a failsafe.

(In the above example I have not included cooling. If this were from an actual playthrough I would have radiant liquid pipes running cooling through the SPOM. Because of the cooling, I build my SPOMs out of normal, rather than insulated, tiles.)



Gas Reservoir


Gas Filter

When you first fire up your SPOM it will take a little while for the gases to stabilize (into oxygen below, hydrogen above). Until then, assume you will have a mix of gases in your oxygen and hydrogen pipes.

To see the mix of gases in your SPOM you can use the Materials Overlay (the square icon top right, or press F4). The goal is for the top area - in particular (on the small SPOM) the tiles under the hydrogen pump, in-between the doors - to only have hydrogen.

If your hydrogen generator is fed anything but hydrogen, it will be damaged. You can solve this issue in different ways. Some examples:

  • A simple solution is to just vent the initial gases into your base, and then hook up your SPOM to your hydrogen generator once the gases have stabilized.

  • If you want to avoid hydrogen getting into your base, you can instead pump the initial gases into a Gas Reservoir and deal with it later, e.g. vent into space.

  • Another option, and what I tend to do, is to add a Gas Filter to the hydrogen pipe. The SPOM produces enough power that you can connect the gas filter to your SPOM's power grid and still have excess hydrogen.


If you're thinking: Can I also add a Gas Filter for my oxygen? And have that powered by my SPOM, too? Then, yes. I don't do this myself, but based on (limited) testing it seems entirely possible. But as the SPOM produces almost ten times as much oxygen as hydrogen, the oxygen Gas Filter will run a lot more frequently than the hydrogen Gas Filter. And use a lot more power.

Such a design will, at times, use more power than one hydrogen generator can produce. So if you want to have two SPOM-powered gas filters, add a second hydrogen generator to meet the increased power demand.

SPOM with oxygen and hydrogen Gas Filters.

​Based on limited testing, this build seems to work. The Gas Reservoir has been swapped out for a second Hydrogen Generator to keep up with power demand. Both filters are powered by the SPOM, and it even produces a trickle of excess hydrogen.


Bootsrapping your SPOM. A temporary power setup to get your SPOM rolling. You can also connect it straight to your heavi-watt wire.

Alternatively, if your goal is to protect Atmo Suit Docks from damage, you can save a lot of power by instead having a Gas Filter placed so it only filters oxygen input to the Atmo Suit Docks.


One way to do this is to split off a "guaranteed to be oxygen" pipe and a "probably oxygen" pipe by your SPOM, running the former through a Gas Filter and having it feed things that would break if they are fed hydrogen. I do this sometimes. (Again, braver people than I trust their SPOMs and don't worry about this stuff.)

And now on to powering up your SPOM.

Your SPOM will power itself once it gets going, but needs some help getting started. You can either connect the SPOM  to your power grid or throw in a few hamster wheels and a battery that you connect to your SPOM. Then disconnect it once the SPOM is up and running.

(Oh, and remember to raise the SPOM's Smart Battery's lower level charge limit so that it is above 0. That way your batteries won't empty completely before the hydrogen generator kicks in.)

That's about it - time to get building! Once you are comfortable with SPOM basics, start modifying the designs to fit your style and needs.


The most difficult thing with any new build, for me, isn't the actual building - it's getting up the nerve to start. Here are links to detailed pictures of two SPOMs and various overlays, to help you on your way to unlimited oxygen.

The pages linked above also include links to Francis John's YouTube videos explaining the builds.

And now, for those who need a reason to postpone the building of their first SPOM, here are some pictures from a SPOM in the wild for you to look at while you get ready to start building your own SPOM. (You can do it!)


In one playthrough I happened to get a water geyser and an Anti Entropy Thermo-Nullifier close to one another. So I built my SPOM around them.

The SPOM is the large one, aka the Full Rodriguez. (With some small modifications.)

The AETN can't quite handle all the cooling - oxygen comes out at 34-35C. (There are additional cooling loops in the actual base.)

The water pump is powered externally, the two gas filters (one hydrogen, one oxygen) are powered by the SPOM.


Ventilation overview. (The spaghetti is strong in this one.)

The gas piping could probably have been made prettier...



  • The SPOM produces three gas pipes worth of oxygen. (They are the bottom row of six gas pumps - two pumps per oxygen line.)

  • One of the oxygen gas pipes is routed through a gas filter. This pipe is the one I connect to my atmo suit docks (and other things that break if fed non-oxygen).

  • All three oxygen pipes are routed through (polluted) water cooled by the AETN (the yellow pipe sections), then branch off to different parts of the base.


  • The SPOM produces one gas pipe of hydrogen.

  • First it is routed through a gas filter. Then it passes the AETN. Then it branches off to one line that feeds one hydrogen generator and another that goes through a reservoir (to store some backup hydrogen) and on to two additional hydrogen generators.

  • At the base of the gas reservoir is a gas overflow section. Whatever isn't used by the generators is sent on. (It powers a second AETN and fills a canister filler. There are more overflow mechanisms there, and any excess is sent to a hydrogen generator connected to my base's power grid to burn it off.)


I built this when the water geyser was still dormant, so added a pipe to inject water until the geyser got going. The liquid bridge is so the SPOM will use water from the water geyser (rather than the outside water pipe) whenever possible.


I'll conclude this section with a quote from QuQuasar's 2018 SPOM, MKII post:

"Here we go: my second attempt at making a Self-Powering Oxygen Module, or 'SPOM'.

That's a stupid name. Note to self: never use that name for any reason ever. We can't let it catch on."




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