Son of Fermentation Chiller (Or "Better Late Than Never")

Most of you home brewers out there would have heard about this piece of equipment used for temperature control called as Son of Fermentation Chiller. For those of you who haven’t heard of it, imagine a box made of foam board with a thermostat inside which monitors the temperature and regulates it with the help of a fan and ice. Yes, it is powered by ice!

I used to use an ice box to keep my fermenter in. I could monitor the temperature, yes. But I couldn’t regulate it effectively. Now with the construction of my own Son of Fermentation Chiller (SOFC), regulating the fermentation temperature has become easily possible.

Now that you know what this blog is going to be about, let me get down to explaining how I built my SOFC.

SOFC is the brainchild of this man called Ken Shwartz. Here’s the link to from where I got to know how to build a SOFC:


  1. Foam board (2” thick)
  2. Silicon sealant
  3. Adhesive (for foam)
  4. 12V adapters x 2
  5. Thermostat
  6. DC fan
  7. Wood strips
  8. Weather shield
  9. A blade to cut the foam board
  10. Indoor outdoor thermometer (optional)

I got all of the materials listed above either online, or by visiting a few local shops right here in the city where I live (Pune, Maharashtra). Here’s where you’ll get the materials and how much you’ll need:

  1. Foam board:
    I got the foam board from this shop in Bohriali called (if I remember correctly) Popatlal and Sons. Ask specifically for 2" thick foam board. It provides better insulation. I got two boards of 6ft x 4ft dimension. Yes, it was more than what is required, but it comes in specific sizes. This is the costliest material of the lot. It costs around Rs. 1800.
  2. Silicone sealant:
    This you can get in any hardware store. If you don’t have a silicone gun, you might want to buy one since it makes the task way easier. One tube should suffice!
  3. Adhesive:
    There’s a Fevicol adhesive available in the market made specifically for use on foam. Ask for Fevicol SR 505. That’s the one. You will need 2 small containers of it.
  4. 12V adapters:
    You can get these in any electrical shop.
  5. Thermostat:
  6. DC Fan:
    This is the type of fan that you use in CPUs. You can get one at:
  7. Wood strips:
    These are lengths of wood having a square cross-section of about half an inch to one inch. Even these are available at any hardware shop. I got 14ft of it because this comes in specific sizes too.
  8. Weather shield:
    I got this from the same shop I got the foam board from. It's a one sided tape made of foam. They didn’t understand when I asked for "weather shield". But they gave me what I wanted when I explained what it is (again, one sided tape made of foam).
  9. Blade:
    You might already have one at home. Otherwise, a stationary shop.
  10. Indoor outdoor thermometer:
    You will need this only if you want to check the inside temperature. I used a food thermometer and inserted it directly through the foam board. It works for me!


You need to first cut out the following pieces from the foam board. You can use a marker to draw lines so that it’s easier to cut. You might need to do some maths so that you waste very little foam board. There are 8 different kinds of pieces of various dimensions that you’ll require:

  1. Bottom: 29" x 16"
  2. Top: 29” x 16”
  3. Front: 28” x 16”
  4. Rear: 28" x 16"
  5. Side One: 32" x 29"
  6. Side Two: 32" x 29"
  7. Fan: 28" x 16"
  8. Baffle: 24" x 7"

This is the picture I referred to to get a better understanding of how the pieces should be cut. Of course you probably won’t get the foam board sheet in the same size as shown in this picture. But at least you’ll see how to cut the individual pieces.

Now you need to make a little modification to the Fan panel. Based on the size of the DC Fan that you ordered, cut out square pieces on both sides of one end of the Fan panel. You will glue the fan to one of these cut ends later.

After you cut all the pieces, you need to glue them together. Follow this sequence:
  1. Glue the Baffle to the Fan panel. Apply the adhesive to one edge of the Baffle and to the centreline of the Fan. The top of the Baffle should be flush with the top of the Fan panel (where you made the square cuts).

  2. Next paste the Rear and Bottom panels. The bottom edge of the Rear panel should be glued to one end of the Bottom panel.

  3. Now glue the bottom end of the Fan AND the other edge of the Baffle to the Bottom and Rear respectively. Do that in such a way that the Baffle is aligned along the centre of the Rear.
  4. Now you can paste Side One and Side Two on either sides. Both the Side panels should be flush with the floor. It should look something like this at this stage:

  5. Do NOT glue the Top and Front panels since you will need to remove them often to change the ice and while keeping the fermenter.
  6. You can use masking tape to hold the panels together till the glue dries. Remove the masking tape once the glue dries. 
  7. Next caulk all the interior corners, edges, joints using the silicone sealant. Fill in all the gaps which can be seen. Make sure you seal all the possible areas from which air can leak through.
  8. Next you need to paste the wooden strips on the interior of the panels. The wooden panels ensure that there is minimal air leakage. Cut and attach the wooden strips to the inside of the Sides around the perimeter of the Top and Front areas. You can look at the picture to see where all you need to paste the strips.
  9. After you are done with the wooden strips, paste strips of the weather shield (that’s the one sided tape made of foam) on top/front of the wooden strips as required. Add a final strip of weather shield on top of the Front panel.


This little electronic device is going to help you regulate the temperature using the DC Fan and ice. It was tricky, at least for me, to make the various connections to get the thermostat to run. What you want the thermostat to do is to turn the Fan on when the temperature rises above a specific degree and to turn the Fan off when the temperature drops below a specific degree. 

I used two 12V DC adapters; the other option is to use one 12V DC adapter and a 12V cell/battery. But I didn’t want to change the battery every time after it died so I used 2 adapters. I’ll show how to make the connections. Even if you don’t buy the thermostat from where I bought, the basic assembly is going to be pretty much the same.

  1. Cut the ends of both the adapters to expose the two wires inside the insulation. Do the same for the fan’s wires. I don’t really know how to identify the positive and negative ends of the adapter wires, but still I got it right using permutations and combinations. 
  2. Connect one of the wires of Adapter 1 to the GND port of the thermostat. Connect the other wire of Adapter 1 to the 12V port of the thermostat.
  3. Connect the black (negative) wire of the fan to K1 port. 
  4. Connect the red (positive) wire of the fan to one of the wires of Adapter 2. 
  5. Finally, connect the other wire of Adapter 2 to K0 port.

Plug on both the adapters and see if the setup works. The thermostat will be provided with a probe and a separate connection for the probe. Read the manual to know how to set the thermostat temperature. 

Place the fan connected to the thermostat in the notch and paste the thermostat at a suitable place on the front side of the Fan panel. You will need to make arrangements (either drilling holes, or finding a gap between the Side and Top panel to get the wires to come out to the plug. I drilled little holes through the sides for the wires to pass through.

Using the Chiller:

Place the chiller at a convenient location. Plug in the adapters. Place ice jugs in the two squares on either side of the Baffle. Keep your fermenter in the chiller and turn on the thermostat.

Place the Top and Front panels. You can add some weight on the Top panel to ensure that the Top sits snugly on the Front. I inserted a food thermometer in the Top panel to check the inside temperature. That way, you don’t need to open the chiller frequently. Usually the ice in the jugs stays for 24-36 hours after which I have to change it. But that’s in summers. In winters, my guess is that the ice will stay for probably as long as 48 hours. On a hot summer day when the temperature outside is around 40 C, the temperature inside the SOFC which I’ve recorded is as low as 17-18 C.

So that’s actually all there is to it! Actually one more thing, the SOFC also works as a canvas (see the moustache and writings on the side?). You could leave that to your imagination, whatever and if you want to draw.

One advise about the thermostat I’d like to give is to set the backlash temperature to 1 C. This way, the fan won’t switch on and off very frequently. One modification which I did which you can see in the picture is that I’ve pasted a perpendicular piece of foam board on the Top panel. I did that to seal the gap which was present between the Top and Front panels. 

Also, be very slow and precise when cutting the foam board. The more exact square cuts you make, the less air leakage you’ll get, the less sealant you'll require, the less effort it takes to paste the boards. If you come up with more modifications or improvements, write them down in the comments section. Cheers! Happy brewing!


  1. Great post on SOFC.
    By the way the thermostat chip is also available cheaper on
    But this may take a long time to arrive from China.

  2. Hey Partha,

    How much did the whole thing cost you ?

  3. Hey Sapan! Honestly, I checked just 2-3 websites for the thermostat and ordered the cheapest from those.
    Also, I calculated the cost too. It cost me around 2900 (2890, to be precise). But I'm pretty sure you can shave off 500-600 if you get the right size of the foam board. I paid 1800 for mine and I still have got a big piece lying around at home. I thinking of building a mini SOFC from that actually!

  4. Hi Partha, I have been searching for XPS(Extruded Polystyrene) foam boards in bangalore, no luck so far. Looks like you got hold EPE foam board but no luck with that too.

    If anyone knows about XPS or EPE foam boards in bangalore please let me know. Will really appreciate that.

  5. Partha, Do we have option to adjust the backlash temperate, please suggest how to do that.

    1. Hey Aadi! I will try to ask a few people about getting foam boards in Bangalore. Worst comes to worst, you can still use thermocol. Even if the thickness is not 2", you can always stick together a number of sheets of thermocol to get the desired thickness.
      Also, as for the backlash temperature, I long-press the 'Set' button till the display starts blinking. You will most probably get a data sheet along with the thermostat.$_12.JPG

      You can see the images of this thermostat. It'll be something like this. Just find the right value to set and you'll be able to set the backlash temperature. In the thermostat that I just posted the link to, the backlash value can be set at code P1. They'll most probably send a data sheet so it shouldn't be a problem.

  6. How much ICE does this need on an average cycle ? You just mentioned Ice jugs and didnt mention the capacity.

    1. Hi Debankar! Oh yeah I guess I missed mentioning that. So I freeze one 5l water dispenser and one 2.25l soft drink bottle at a time. When I keep the two inside the SOFC for cooling, they last for 24-36 hours. Hope that helps!

  7. I managed to get the Extruded Polysyrene Foam boards that are 2 inch thick. But they are terribly hard to cut with my hack and saw blade. Going to find it tough to assemble. I am just going to use the silicone sealant generously. Will the caulk gun help with the sticking?

    Also forgot to get the weather shield but have the xps pieces will that work? What do you think?

  8. Hey Radha! It's quite surprising that it's that hard to cut extruded polystyrene boards using a hacksaw. But I do remember I had taken almost 2-3 days to cut the sheets. But don't worry about assembling. If you get the adhesive that I mentioned, it will make sure the SOFC will stay in place.

    The caulk gun will be a big help to especially reach the corners. The open areas won't be much of a problem. But the caulk gun will make your job easier when it comes to applying the silicone in areas inaccessible by hand.

    Yeah, the xps pieces will work. Basically the weather shield ensures that the assembly fits snugly. The xps pieces should do the job too! Good luck with your project!

  9. Your blog provided us with valuable information to work with. Thanks a lot for sharing. Keep blogging.
    EPE foam suppliers in delhi Ncr

    1. Thanks for going through it! I'm glad it is of help to you :)

  10. Where did you get glass fermenter?

    1. That's a plastic fermenter. No idea where to get glass fermenters here.

  11. This comment has been removed by a blog administrator.


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