I have been using a combo HLT/heat exchanger since I added HERMS (Heat Exchanger Recirculating Mash System) to my original gravity feed brew rig. A friend had an old keg and wanted something just like mine so I offered to do the conversion for him, essentially duplicating my original build. I don’t weld so it would have to use weld-less fittings like those I used for mine; if you have the technology you could swap in welded fittings for those described in this article.
Build a DIY Heat Exchanger
Step one is to gather the tools and components required. For the heat exchanger coil we selected the same one I had used, a 50 foot, one half inch diameter coil from Stainless Brewing (about $100). We chose heavy duty bulkhead compression fittings to mount it (about $25 ea. from the same source). We selected a weld-less bulkhead fitting with integrated 5/8” dip tube (about $34), a weld-less sight glass kit (about $27), and a weld-less bulkhead with 90 degree elbow for the water inlet (about $18) from Brew Hardware. The three piece ball valve ($10.95) and the Camlock fittings came from Bargain Fittings.The thermometer came from my parts bin; Bargain Fittings has nice ones for $17 or so if you need one.
Tools included my little 10V lithium drill motor for all holes except those using the step bit, my big 14V NiCad drill motor for the step bit, 1/8”, 1/4”, and 3/8” twist drills, a step bit, 1/2” and 13/16” Greenlee punches, miscellaneous wrenches, and a center punch.
I recommend using a center punch to ensure accurate hole locations and to avoid marring from a skittering twist drill. Carefully select and mark each hole location. Important factors to consider include the height of the ball valve/diptube fitting (you want the diptube to end up at the correct height), the location of seams and bulges in the keg (fittings won’t be reliably leak-proof unless mounted in a flat area), and the desired orientation of the ports in the end product.
Once the holes are located, I start each hole with a quality 1/8” twist drill. I then open the hole up to whatever size is required for the step drill or Greenlee punch that will make the final hole. I MUCH prefer the Greenlee punches. In this project, I used a step drill for a couple of holes just so I could show one being used in the article. NOTE – the keg is stainless steel. It is relatively easy to drill, but only if the twist drill or step drill is sharp and oil is added frequently both to lubricate and to cool the tool.
Here you can see the 1/2” punch being used to make the hole for the sight glass. At the left it is partially disassembled and ready to be placed in the 1/4” hole. At the center you can see the outside portion when ready for action and at the right you can see the inside portion.
Installing the Coil
The above shot offers an opportunity for a couple of reminders. ALWAYS tape the fittings before assembly. This is only partially to prevent leaks. It is of equal importance that it lubricates the threads and prevents galling. Stainless pipe threads assembled without tape can gall so severely that they may as well be welded. Also note that all hardware has been installed IN BETWEEN the vent holes in the base ring rather than above any of them. Hot gases will escape these vents and can damage or destroy thermometers and valve seals.
The HEX coil is suspended within the HLT by the two bulkhead compression fittings. These use stainless steel ferrules, meaning that they can easily handle the ten pound free weight of the coil. It also means that if you ever remove the ferrules they will need to be replaced. They are not reusable.
In practice, wort is drained from the bottom of the MLT and pumped into the bottom HEX fitting. The wort then leaves by the top HEX fitting and is fed back into the MLT at its top. The direction matters only because this configuration results in the shortest hoses and thus the least heat loss.
The 1/2”, 50′ coil is very effective. I measure the temperature of the wort coming out of the HEX and it is generally the same as the HLT water temperature. The water level in the HLT is normally maintained at a level that completely covers the coil but I have fiddled with it only half covered and it was nearly as efficient.
Final Considerations on Your DIY Heat Exchanger
Note that I have installed no valve on the lower (input) side of the HEX coil. This means that unless the top (output side) is connected to a closed path the contents of the coil will drain immediately if the bottom is disconnected. In my system this isn’t an issue because the output is connected to an Auto-sparge that I can lift to close it while moving hoses around. My friend will be using a sparge head with its own valve.
The sight glass listed above includes the necessary lettering to calibrate it. We will get around to that at some point. It is just a matter of leveling the pot, adding water one carefully measured gallon at a time, and marking the tube as you go.
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