A heat exchanger boiler system has a single boiler. The water temperature in the boiler is kept at steam temperatures (higher than what you'd use to pull a shot). This water in the boiler can be used directly for the steam wand.
In heat exchanger espresso machines here is an additional tube within the boiler. When the barista pulls a shot, the water flows from the water source through this tube located in the boiler. As it flows through this tube, it reaches the appropriate temperature for brewing (around 200 degrees give or take) and flows into the group head for shot extraction. Any leftover water in this tube after the shot will most likely need to be flushed as it will keep getting hotter because of the temperature of the steam water.
Because of how this process is designed, it means that the user doesn't have direct control over the water temperature that's being used for brewing. Instead, the user changes the temperature of the water that's being used for steam which will indirectly modify the temperature of the brew water passing through the pipe.
BENEFITS OF HX BOILER MACHINES:
- Water is fresher since it comes direct from a water source and isn't sitting in a boiler.
- Uses less energy than a double boiler system since only one boiler needs to be heated.
- Usually, run cheaper than double boiler machines.
- Great for the person who does a lot of cappuccinos or other milk-based espresso drinks.
- Better for commercial applications than a single boiler, but super high volume operations would do better with a double boiler.