Single Boiler, Heat Exchange, Dual Boiler… What’s the difference??

Which machine is right for me?

Some machines are great for black coffees but not great for milky coffees, others are great for making a couple of coffees but are not suited to handle multiple back to back coffees. Some will give great consistent results and flavour but lack the flexibility to make adjustments that a true coffee nerd seeks. There are some other factors to think about (particularly when going full coffee nerd) but below is an overview of the three main classes of high end home coffee machines.

In the prosumer coffee machine world, there are three general classes of machine: Single Boiler, Heat Exchange (HX) and Dual Boiler. Each category of machine have positives and negatives and will suit different users. Below is a quick summery of each and scroll further for more details.

Single Boiler machine has the smallest footprint but cannot brew coffee and steam at the same time, there is a 1-2 min wait between brewing and steaming and due to the small boiler size, are not suited to steam large quantities of milk.

Heat Exchange (HX) machine is generally bigger that a single boiler and can brew and steam at the same time and due to the large steam boiler, can produce enough steam enough milk for many coffees. The performance of a we set up heat exchange machine will be on par with a dual boiler.

Dual Boiler (also known as double boiler or multi-boiler) is generally the biggest and like the HX can produce large amounts of steam but also has the added flexibility of being able to adjust the brew temperature and steam temperature independently.

Boiler types

Single boiler

A single boiler machine uses the same boiler to produce hot water for coffee extraction and to produce steam. The boiler heats the water to brew temperature for brewing the coffee, then once you have made your espresso, the machine is switched into steam mode and takes a minute or so to heat the water to steam temperature for steaming the milk.

Single boiler machines typically have a much smaller steam capacity than their heat exchange and double boiler counterparts and are not really designed to make more than 2 milk based coffees at a time. This makes them much more suited to black coffee drinkers who might occasionally make a milk based coffee.

The temperature can be controlled either by thermostat or digitally (through a PID). PID based single boilers can be very temperature stable, giving good flavour consistency, whereas the thermostat based single boiler models can fluctuate a fair bit in brew temperature, which can make getting consistency in flavor difficult.

Will suit:

  • Black coffee drinkers who might do the occasional milk-based coffee


  • Lower cost
  • Small footprint


  • Can’t brew and steam at same time
  • Small steam capacity
  • 1-2 minute wait time in between brew and steam
  • Not designed to make multiple back to back coffees

Heat Exchange

Unlike a single boiler, heat exchange machines can brew and steam at the same time as there is a separate water path for the brew water and the steam. They have one big boiler (means good, consistent steam), with a heat exchange pipe that runs through the centre which feeds the grouphead.

A well designed and set up heat exchange machine will give good temperature stability and plenty of steam to pump out coffee after coffee. Though other heat exchange designs can have a tendency to overheat the brew water, feel free to contact us for guidance on which machine would best suit.

Will suit:

  • Black and milky coffee drinkers alike


  • Brew and steam at same time
  • Big boiler for plenty of steam
  • A well designed and setup machine will give great temperature stability


  • If not well setup/designed, can overheat the brew water
  • Lacks flexibility of double boiler machine

Double boiler

Flexibility is one of the key features of a double boiler machine. These machines have an individual boiler for both brew and steam water. Not only can brew and steam at same time, you can also independently control brew and steam temperatures.

As a few degrees difference in brew temperature can change the flavour of an espresso, having the ability to change this temperature allows the user to experiment with different flavour profiles by extracting coffee at varying temperatures.

Being able to independently control the steam temperature allows you to control the pressure at which the steam comes out of the wand.

Will suit:

  • Milk and black coffee drinkers alike
  • Those who want to experiment with how brew temperature effects flavour. The flexibility of being able to play around with brew and steam temperatures independently.


  • Best temperature stability
  • Flexibility for those wanting to experiment with brew temperatures
  • Can increase steam pressure without affecting brew temp
  • Brew and steam at same time


  • Usually largest footprint