For our partner’s C1Net project we needed a steady supply of very cold water. You can buy recirculating chillers but they’re pretty pricey for what’s basically a jumped-up refrigerator and a pump. We built our own.


Part Link Cost
2x 3L tub N/A negligible
Mini freezer Currys £79.99
Submersible pump Aquarium pump £13.95
Microbore copper coil (10mm) Microbore copper tubing £22.99
Silicone tubing 10mm Negligible
Insulation board Insulation board £5.02

Cold reservoir inventory

Build Instructions

1. Remove door from freezer. Keezer (keg freezer) builds online often drill through doors and fit taps but we wanted to keep the door intact. A replacement door was easily assembled by sawing a piece of insulation board to door size. Two holes were drilled for the silicone tubing.

2. Carefully coil the copper tubing to fit into the tub as below.

 copper coil Copper cooling coil

The copper coil was shaped by hand to fit into the tub. Take care not to kink the coil. Note some people pack the tubing with sand before bending as this supports the walls against kinks.

3. Fill tub with water, immerse coil. Place inside freezer.

4. Connect silicone tubing to copper coil and push through door holes.

5. Connect one end of tubing to submersible pump.

6. Submerge pump in part-filled tub (we used 1.5L). Turn on. Ensure water is drawing through the entire system.

7. Seal door in place (we used autoclave tape).

8. Turn on freezer and wait.

Do not turn off the pump or the water in the coil will freeze rapidly. Flow rates, external tub volumes and ambient temperature determine the extent of water chilling. We found the freezer reached -10° C within an hour. Within four hours the circulated water held steady at 4° C.

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Assembled chiller unit