Heat Exchanger vs Double Boiler Machines: Which Is Better?

Want to master the art of latte at home? Then you need an espresso maker that can brew coffee and steam milk at the same time. And that leaves you with two options: either a dual boiler or a heat exchanger.

There are pros and cons to both choices, so keep reading to find out which is right for you!

How does a heat-exchanger espresso machine work?

A heat exchanger (HX) machine only has one boiler, but you can still pull a shot of espresso and steam milk simultaneously. 

How is this possible? 

An isolated section within the boiler maintains a cooler temperature for brewing, while the rest stays hot enough for steam. Typically, a thermosiphon circulates water from the cooler region of the boiler to the group head. This keeps the group head hot and at a stable temperature while also keeping the brew water cooler than the rest of the boiler. 

While this may sound tricky to calibrate, the best manufacturers for home espresso machines have had decades to perfect the system. It works exceptionally well.

Controlling boiler temperature

In the past, the temperature of a heat exchange boiler was controlled using a pressure stat. A pressure stat is a mechanical device that monitors the pressure in the boiler and converts it to a temperature. Recently, more HX machines are relying on solid-state PIDs, which are more accurate and keep the temperature more stable. 

As a bonus, they also last longer.

Without a PID, an HX machine needs a cooling flush before brewing to lower the temperature, whereas a PID can control temperature without this step. However, the cooling flush system has an advantage in that it is much more responsive than a PID. 

The trade-off is that the barista won’t know the precise temperature. You may need to wait a little longer with a PID once you set the temperature, but you’ll know exactly what it is. That makes it easy to produce great espresso consistently. 

Pump styles

An HX machine can have either a rotary or vibratory pump. However, vibration pumps are far more common. Generally, rotary pumps are considered higher-end because they’re quieter and allow the machine to be plumbed directly to a water line. However, some users prefer vibration pumps because they ramp up to pressure more slowly, allowing a more gentle natural pre-infusion.

How does a double-boiler espresso machine work?

A double-boiler machine is much simpler to understand. It has two separate boilers. A smaller one is at a lower temperature for brewing, and a larger one at a higher temperature for steam. 

At this point, most prosumer-grade dual boiler espresso machines are equipped with dual PIDs so that you can control the temperature of each boiler independently. This means you can change your brewing and steaming temperatures quicker and with more accuracy than the HX machines.

Experts agree that temperature precision is crucial if you want to highlight particular flavors of a coffee (1).

Another nice feature of a dual-boiler machine is that you can turn the steam boiler off if you’re making just espresso. This means a faster heat-up time and lower energy consumption.

Which is right for you?

Let’s summarize our findings so you can decide what style of espresso maker meets your needs. And if you’re still unsure, check out this helpful video with Steven from Home Grounds:

Opt for a double-boiler if:

• You enjoy experimenting with single-origin beans and different roast level, where temperature accuracy and stability is vital.
• You want to plumb your machine to a water line.
• You’re worried about the volume of a vibration pump.

Opt for a heat exchanger if:

• You want to be able to make a lot of milky drinks back to back.
• You want plenty of steam power.
• You need a compact machine.