Build a Flow-Through Thermometer: Projects

Want to know the temperature of the water exiting your counterflow chiller? Get in line — an in-line thermometer that is.

So you’ve got a great new counterflow chiller to knock down your boiling wort to yeast pitching temperatures but you aren’t sure how high of a cooling water flow rate you need to do the job? You need an in-line thermometer to give
you hands-free and real time feedback on the temperature of the wort as it leaves
the chiller.

This type of thermometer is positioned after the “wort out” connection on a counterflow chiller and is connected on either end by vinyl tubing. The wort flows out of the chiller, through the in-line thermometer and then into a fermentation vessel (carboy, bucket, etc). The in-line thermometer shows you temperature changes in the wort as it happens. This allows you to adjust the flow rate of cooling water going into the chiller to get the target pitching temperature you need for whatever type of yeast you might be using.

Sure, you can do this with a normal thermometer by dipping it in the wort that’s already in the carboy, but this
can be messy and poses a potential bacterial contamination risk. Also, an in-line thermometer allows hands-free temperature monitoring.

If you have cool or cold ground water, using such a thermometer will also help you save money by allowing you to reduce excess water usage during cooling. Brewing is a water-intensive process, and if you can dial in the exact flow rate you need, you can potentially save several gallons of water per brew session. In addition to the cost savings, cutting your water usage is also environment-ally friendly.

Commercially available in-line brewing thermometers run about $40 at retail, but you can put one together yourself in just minutes for about $10. A quick trip to your local hardware store and pet shop will get you everything you need. We’ll be using a common self-adhesive aquarium thermometer (very similar to the stick-on thermometers often used on carboys) with a temperature range from 64 ºF to 86 ºF (18 ºC to 30 ºC) as the workhorse of this project. This temperature range coincides with the recommended pitching temperatures for the vast majority of yeast strains.

There are two basic materials options for this project, depending on your personal preferences: metal or clear PVC. Metal conducts heat better and allows the thermometer to adjust to temperature changes quickly. Clear PVC is lighter and cheaper and allows you to see the wort as it flows through. For some people, being able to see the wort is important, so if you fall into this category, the PVC is your best option.

Metal mania

For the metal thermometer, you’ll need the following parts:

  • 1/2-inch x 3-inch pipe nipple, brass [Fig. 1]
  • Two 1/2-inch FPT to 1/2-inch hose barb fitting, brass [Fig. 1]
  • LCD self-adhesive aquarium thermometer, small vertical style [Fig. 4]
  • Teflon pipe tape
  • Clear plastic packing tape

Before assembling this project, the brass parts should be washed with warm water and mild soap to remove any dirt and oil and then dried. The first step is to give the threads on both ends of the pipe nipple a liberal wrapping of teflon tape [Fig. 2]. It is very difficult to get a good seal with threaded metal fittings without using pipe tape. Now screw in the hose barb connections to either end of the pipe nipple [Fig. 3]. Hand-tightening may be enough to get a good seal, but you should give each connection a little extra torque with a wrench just to be safe. Even the smallest leak in your thermometer will give you a headache on brew day by adding to overall cleanup time. (Over time, temperature fluctuations can cause the metal to expand and contract, which can loosen the fittings. You should check the tightness of the fittings after every third or fourth usage).

Now that all the fittings are snugly connected, affix the LCD thermometer to the pipe nipple as shown in Fig. 5. The small vertical LCD thermometers commonly available in pet stores are generally about three inches high, which is a tight fit on our 3-inch pipe nipple. You may have to trim a little off the bottom of the thermometer strip. When I assembled this project, I needed to trim off the name of the manufacturer in order to get it to fit on the pipe nipple. Trimming will not in any way impair the operation of the thermometer, so don’t be shy about customizing it to fit your project. Since they retail for about $2 at most pet stores, go ahead and buy two of them in case you trim a little
too much.

To finish off the in-line thermometer, give the pipe nipple a turn or two of plastic packing tape. The stick-on strip thermometer was designed to be used on flat glass rather than concave metal, so the clear tape will help keep it in place long after the adhesive backing wears out.

Plastic voyeurism

If you want to go the clear plastic route, here’s what you’ll need:

  • 1/2-inch x 4-inch* pipe nipple, clear PVC [Fig. 6]
  • Two 1/2-inch FPT to 1/2-inch hose barb, PVC or polypropylene [Fig. 6]
  • LCD self-adhesive aquarium thermometer, small vertical style [Fig. 4]
  • Teflon pipe tape
  • Clear plastic packing tape

* You may have difficulty finding clear PVC at your local hardware store. If so, you can order it online from U.S. Plastics ( using part number 34349. *Note: The 3-inch clear PVC pipe nipple that U.S. Plastics stocks has less non-threaded surface than the equivalent brass part, so I recommend that you get the 4-inch part. For the hose barb fittings, you can use any available plastic material that is safe for potable water.

Putting together a see-through thermometer is nearly identical to the steps involved with the metal version: Wrap the threads with pipe tape [Fig. 7], screw in the hose barb fittings [Fig. 8], and affix the LCD thermometer strip and wrap it with packing tape [Fig. 9].

Performance: Metal Versus PVC

The strip thermometer used in this project reacts to temperature changes surprisingly fast considering its low price. I tested both a metal and clear PVC version of this project to get a rough idea of how it would perform in a situation of quickly changing flow temperatures.

Starting off with warm tap water (approximately 90 ºF or 32 ºC) flowing through the thermometer, I quickly shifted to much cooler water (approximately 60 ºF or 16 ºC) and noted how long it took the thermometer to register the change. The metal thermometer took about 8 seconds to adjust to the change, while the PVC thermometer took about 15 seconds. I did not test under “laboratory conditions,” so take the above results as rough estimates of performance.

Variations on a theme

The above parts and methods are merely suggestions. Feel free to substitute larger or smaller fittings to suit your individual brewing setup or use stainless steel instead of brass. Above all, don’t be afraid to be creative. And let us know if you develop an improvement on the design. We’d love to hear about your success and innovations.

from BYO

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