Introduction: Chest Freezer Carbonator for Unlimited Seltzer

    Having a growing addiction to carbonated water, I had to find a more efficient and quick way to carbonate water. One day, I read this Instructables, written by piyoman, where they converted a bar fridge into a on-demand carbonated water dispenser (which I highly recommend reading through). After reading this, it gave me an idea to repurpose my once-apon-a-time keezer (beer refrigerator using a chest freezer).

    For those who have never thought about the mechanics of carbonating water, the process involves combining cold water with a source of pressurized carbon dioxide. When this occurs, the carbon dioxide dissolves into the water forming carbonated water. While this process can be done using room temperature water, the amount of dissolved carbon dioxide decreases as the temperature goes up. Systems like a SodaStream use a container filled with water as the water source, and a carbonating base which contains a canister of carbon dioxide. When you attach the container to the base and press the button, pressurized carbon dioxide mixes with the water causing some of the CO2 to dissolve and some to be released by the pressure valve.

    For this setup, instead of a container that is filled with water, we have a vessel which contains a constant CO2 supply and a water level switch which injects water into the system. This allows an unlimited supply of carbonated water as there is a constant CO2 in the vessel for the water to mix with.

    With that, lets get started!


    As I already had the chest freezer I will link to some equivalents, but will not add the cost to the total.

    Total: $832.58

    Step 1: Foreword

    To start, I already had a chest freezer, which used to have kegs of beer inside connected to a CO2 system and a few taps. I never fully finished the wood collar, which use to be 2x4's screwed into a square, so the first step was to redo this. I bought some poplar boards and went about staining and sealing the collar. Step one was a great success and it already looked better.
    Living in an apartment, I was forced to use existing plumbing, because of this, I had to use smaller supply line than required. Because of this, a few additional parts were required but no major modifications to the existing plumbing was required. I opted to tie into existing sink valves. This meant I would be running 1/4 PEX which is smaller than what the Big Mac requires (it requires a 3/8 supply line). To solve for this, I added a expansion tank inline with the input to the Big Mac. The expansion tank acts as a water capacitor and allows the pump to receives the supply it requires. If you are able to run a 3/8 supply line, you should do that, you will need to make some modifications to the supplies/fittings, but you would not need the expansion tank, and the related fittings. See the details below for more information about the expansion tank setup.

    I also added a second tap for still refrigerated water, which I added because why not, but also is not needed. This will save some money too since you do not need the additional perlick faucet and shank.

    One other thing to note, I am lucky to have very good water from the city. Not everyone is as lucky to have crisp water to their house. Because of this, I opted for a simple carbon/sediment filter (the CuZn filter) to simply filter anything that may be there, but others may need a reverse osmosis filter to clean the water. The RO filter usually comes with some kind of expansion tank too, which could be used instead of my home made tank. piyoman details a lot more information about RO systems.

    Step 2: Pre-plumbing

    Before we get into the plumbing part, let me quickly overview my chest freezer. I am using an 8.8 CU chest freezer that I added a temperature controller to allow the freezer to maintain above freezing temperatures. You can choose a smaller freezer too as I have plenty of extra space left over. I have the temperature controller sensor suspended in a glass bottle (beer bottle) filled with water. This is placed at the lowest point in the freezer to ensure I do not cause freezing.

    To mount my faucets, I built a collar between the freezer chest, and the lid. It was built with some poplar boards. I drilled three 1 inch holes to mount the shanks (added a spare in case I want to add a beer tap later on). As well as an 1.5" hole in the back to run power, temperature sensor and the water inlet. I used some pipe insulation to plug that hole.

    Step 3: Plumbing

    Plumbing turned out to be the toughest part. Most of the time was trying to go from one size to another. What made things even more tricky, was all the connections touching carbonated water must be stainless steal. Do not use brass or copper as the carbonated water will leach copper out and cause copper poisoning (which does not sound fun, so stick to stainless).

    I have included a rough diagram of the setup. However lets jump into the details:

    Starting from the sink, I disconnected the 3/8 compression fitting and added the 3/8 compression tee to allowing me to connect the 3/8 compression to 1/4 sharkbite fitting as well as the sink fitting. From there, I ran the 50 foot 1/4 PEX along the floorboard over to the chest freezer. Before terminating the PEX, I added the check value, and a ball valve (I also recently added a flow sensor connected to an arduino to monitor water usage, this was added before both of these). Finally I used the second 1/4 sharkbite to 3/8 compression to terminate the connection. This is fed into the 3/8 right angle male to male connector that came with the 3/8 to 3/8 compression braided line which (the braided line) is fed into the chest freezer connecting to the water filter inlet (which uses the same 3/8 compression fitting as the braided line).

    The filter comes with a short 3/8 to 3/8 compression line which connects between the filter and the 3/8 compression to 3/8 MIP adapter that also came with the 3/8 braided line. We than use a 3/8 FIP to 3/8 barb and use the 3/8 braided vinyl from here on out. At this point, we want to add our expansion tank, so we use the 3/8 barb tee to split the line into three. One goes into the 3/8 barb Big Mac input, the other goes to the expansion tank setup. (See the next section for this setup)

    The output of the carbonator is a 3/8 barb where as the tap shank is a 5/16 barb. While 1/4 is still not exact, its close enough and I have had no issues. From the Big Mac output, I ran a short section of 3/8 braided vinyl and used the stainless steal 3/8 barb to 1/4 barb to use the 1/4 braided vinyl tube to run to the shank.

    For the two taps, you want to make sure the tap with the flow regulator is on the carbonated water line. This line is going to have a higher pressure than the water supply and the flow regulator will ensure a controlled flow is maintained during the pour.

    The final bit of plumbing is the CO2 line. The CO2 regulator has a 3/8 barb while the Big Mac has a 1/4 barb. Once again, short section of 3/8 braided vinyl to the 3/8 barb to 1/4 barb followed by the 1/4 braided vinyl to the Big Mac. Its worth noting here too, CO2 regulators differ, standard beer regulators max out at 60 psi. For this application, you need higher pressure, in the 100 psi range. The soda regulator I reference can regulate to higher pressures which is useful for this application.

    Beyond from the expansion tank, this will get thing up and running. Make sure to use the ear hose clamps at all the terminations between barb fittings and the vinyl tubing. I never used these clamps before but they are very easy to use (some strength needed). So far I have had no problems with any of the connections. Also make sure to use PTFE pipe sealant on all the pipe threads (compression fittings do not require sealant, only the MIP and FIP connectors require the tape).

    Step 4: Expansion Tank

    As mentioned earlier, because I was running a 1/4 supply line to my chest freezer, I was experiencing issues with flow rate. This was apparent by the sound of the pump struggling to satisfy. To prevent stress to the pump and motor, I added a inline expansion tank to act as a water capacitor; allowing the pump to draw from the water stored in the expansion tank in addition to the supply line. After the pump fills the tank, the supply slowly replenishes the expansion tank for use later on.

    While I was at it, I added a pressure valve as well as a refrigerated still water tap. As you may have noticed from the image, there are a lot of fittings required to go from the 3/4 MIP from the expansion tank to the 3/8 for the supply and a 1/4 for the still water tap. To start, work from the fittings on the expansion tank and work up, making sure to use teflon tape between each connection (I ran out towards the end and used gas teflon tape).

    It starts with the 3/4 FIP to 1/2 FIP adapter -> 1/2 MIP to 3/8 FIP -> 3/8 MIP to 3/8 MIP -> 3/8 tee -> 3/8 MIP to 3/8 barb. The other side of the 3/8 tee uses the 3/8 MIP to 1/4 FIP -> 1/4 MIP to 1/4 MIP -> 1/4 tee -> 1/4 MIP to 1/4 MIP -> 1/4 ball valve (optional, not required, but nice to have) -> 1/4 MIP to 1/4 barb. Finally the last connection on the 1/4 barb is where the pressure gauge is connected.

    The 1/4 barb at the end connects to the other tap shank for the still water tap. The 3/8 inch barb connects to the 3/8 tee in the supply line that the last section talked about.

    Its also important to understand how expansion tanks work. There is a rubber bladder that splits the tank in two. On the opposite side to the 3/4 MIP, there is a air tank which initially is charged to 40 psi (typically, but check your tanks manual for its initial charge). This charge is what allows the tank to store water and return it under pressure later on. Its important to note, as more water enters the tank, the pressure in the air bladder will grow. I have found that the factory pressure is a good starting point. If you notice that the motor struggles towards the end of the fill cycle, it means the tank is over charged and some of the charge will need to be released.However, if your water pressure is high, you may need to add more air to the tank. Its worth noting, air can be added or removed using a bike pump and the schrader valve on the bottom of the expansion tank.

    As a reference point, my water pressure swings from between ~40 psi up to ~100 psi. Its worth monitoring the pressures to see how high yours reaches. The expansion tank is rated for a max difference of 80 psi. So for my setup, the initial charge of 40 psi means the max difference would be 60 psi which is below the max difference of 80 psi. Its also worth noting, because we have a check valve, our system will maintain the highest pressure during the day.

    Step 5: Initial Fill

    If everything went to plan, you should be able to start letting the water flow! The Big Mac instructions list the initial operating instructions which involve opening the black pressure relief value and turning the water on. Because the value is open, the tank will begin to fill, even though the pump is still disconnected. Once the water begins to pour out of the pressure valve, close the value. At this point, the tank will be full of water. ]You can now pressurize the system with CO2.

    The objective for the CO2 pressure it to pressurize it slightly above the water pressure to prevent water from filling the tank while the pump is off. For my setup, I have pressurized the system to 100 psi (the carbonator has a max psi of 120 psi). This leads to very strong carbonation (which is my favorite, so no complains). Less pressure means less carbonation, but you may need to install a water pressure reducer if this is desired.

    Once the CO2 has been connected, you can begin flushing the system. Turn the power on and open the tap until the motor kicks in. It will take a few pump cycles before the carbonation equalizes. It will also increase in carbonation as the water becomes refrigerated.

    Make sure to check for leaks at this point, last thing you want is to flood your chest freezer.

    Step 6: Wrap Up

    If everything is looking good, go ahead and turn the freezer/refrigerator on and let it come down to temp. I have set my controller to go down to 1.3°C and turn on at 4.7°C. This allows some buffer where the temperature will continue to fall after the compressor turns off. This is also a good temperature for drinking water and I have been happy with this setting. Just make sure on the initial cooldown that the temperature will fall much below the designed cutoff so be aware and adjust accordingly (cut it off at 2°C for example).

    As far as reoccurring cost, the CuZn filter is rated for 50,000 gallons which they calculate to be about 5 years (Ill guess itll last longer since its for drinking water and not under a sink). The CO2 tank will also need to be refilled, my current guess is my 10lbs tank will last for 7 months (based on my 5lbs tank connected to a sodastream lasting about 3.5). However this system should be more efficient than a sodastream so my hope is it'll last longer (Ill be sure to calculate it base on liters once I have to replace it). Finally, the expansion tank may have to be replaced at some point. They are known to fail eventually, but my hope is it'll last 10 years.

    The system should be pretty maintenance-free. The Big Mac does have a sediment filter, but since we have our own filter, I do not expect this to require cleaning. The only other thing that will be needed is to recharge the dehumidifier every month or two. The Big Mac is not designed to be cooled so its best to keep the environment as dry as possible to prevent moisture buildup on the pump.

    Hopefully this helps you build an unlimited seltzer dispenser. During my build I could have used a parts list for a setup which did not use a RO system. Since building this, I went and added a water flow sensor using an arduino and a LCD to keep track of water usage. Once I have some numbers, I can post the cost per liter. With that, thanks for reading and I hope this has inspired you to build your own!