Espresso Machine Boiler Designs

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Deciding on an Espresso Machine - Comparing the Three Major Designs

If you have been shopping for an espresso machine boiler you already know that there are a lot of choices; size, color, cost, and most importantly, function, all have to match your personal requirements. Starting with the basics, we can divide the choices into three major functional coffee machine design patterns. Let's see if we can help you understand the differences and help you find the category of machine that can best suit your needs and desires.

Single Boiler

Rancilio Silvia is our top selling example. A single boiler espresso machine is just as the name describes. It has one boiler to heat the water to brew espresso and can also dispense hot water for tea and Americanos. That same boiler is also used to make steam to stretch milk for making cappuccinos and lattes. While single-boiler machines offer good performance in a reasonable cost range, their main drawback is that when switching from brewing to steam modes takes a bit of time waiting for the machine to bring the water to the temperature to create steam.


• Many models to choose from
• Compact size compared to the other categories here
• Good cost:performance ratio
• Generally dependable as they are mechanically simple


• The one boiler has to make hot water to brew and then be switched to make steam which takes a few additional steps each time a mode is switched (brew to steam, and then steam back to brewing).
• Takes longer to make a milk-based drink than the other designs mentioned here.
• Not well suited for entertaining or serving groups
• Brew temperature not adjustable
• Should not be left on, unused, or unattended for long periods
• Boiler needs to be manually filled after steaming

Heat Exchanger

Quick Mill Andreja Premium EVO is a good example. In simple terms, an espresso machine with a heat exchanger is sort of like a boiler inside a boiler. There is a large, partially-filled boiler that is kept under pressure and temperature. As in a pressure cooker, this keeps the water at a temperature around the boiling point. Steam is always available in the upper portion of the boiler for steaming milk, and hot water is always available, drawn off the lower portion of the boiler.

A separate metal tube passes through the boiler. This tube is always filled with water and that water is only used for brewing espresso. The thermal energy in the hot water boiler is transferred to the heat exchanger tube to heat the brew water. This keeps a fresher supply of water available for brewing espresso.

The main benefit of this design over the single boiler is that you can steam milk and brew espresso at the same time since the source for steam is independent from the brewing path.


• Larger capacity boilers that lend themselves to greater temperature stability
• Adjustable brewing temperature
• Better suited for serving greater numbers of beverages in a session then single boiler
• Brew and steam simultaneously
• Able to be left on for extended periods
• Boiler automatically kept at the proper level


• Usually larger than single boiler machines
• Cost more than single boiler machines
• During idle times the brew water can become overheated requiring a flush to cool before brewing espresso.

Double Boiler

Rocket R58 is a fine double boiler espresso machine. As the name implies, double boiler machines have two separate boilers. One boiler is the same as found in the heat exchange machine to store hot water and steam. The second boiler is solely for brewing espresso.

While the steam boiler is only partially filled with water to leave room for steam, the second boiler is the brew boiler. It is always completely filled with water, kept at a preset temperature, ready for brewing espresso. This increases brew-temperature stability and consistency.

The dual boilers makes it easy to steam milk and brew espresso at the same time without affecting the brewing temperature.


• More accurate brewing temperature control
• Ability to control temperature of brewing water and hot water temperature separately
• Ability to brew espresso and steam milk simultaneously
• Well suited for serving greater numbers of beverages in a session
• Able to be left on for extended periods
• Boilers automatically kept at the proper level


• More expensive than the other two designs mentioned here because of the additional boiler and its control system.
• Larger than single boiler machines and some heat exchanger machines

If you are not sure as to which model best suits your needs, please feel free to contact 1st in Coffee. We would be glad to answer all your questions and guide you to your new espresso machine!

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