Comparing the Thermoblock vs the Boiler, the Thermocoil and Other Espresso Machine Heating Systems..
The key to a great espresso shot is consistency. Consistent grind, consistent tamp, consistent temperature. But how do espresso makers manage to deliver shot after shot at the perfect 93 degrees Celsius?
Today there are four primary technologies that heat water for espresso: thermoblocks, boilers, heat exchangers, and thermocoils. Each technology comes with its own benefits and drawbacks.
How a Thermoblock Works
A thermoblock is metal block with embedded heating elements and a pipe for water. As the water travels along the length of the pipe it picks up heat from the block, exiting at the desired temperature. The water is in contact with the thermoblock for a short time, but in that time it can flash heat to temperatures high enough to generate dry steam.
The simplest thermoblocks are fabricated out of two plates of metal with a spiral route cut into it for the water to travel through. A gasket is compressed between the two pieces, preventing the system from leaking. Other thermoblocks are simply a length of pipe with a heater attached along its length. (1)
Common materials for thermoblocks include aluminum, brass, and stainless steel. Some thermoblocks use a composite design with stainless steel pipes encased within an aluminum body.
Thermoblocks are inexpensive to produce and also are energy efficient as they only heat water immediately prior to it being used. Many superautomatic espresso machines (like a few ones here) feature a thermoblock system that makes heating water quick. While thermoblocks are able to generate hot water extremely rapidly, their temperature control is less perfect than some other heating technologies.
It is common for espresso machines (check out some of the best ones here) to use thermoblocks on the steam side and a boiler for the brew side. This allows the thermoblock to do what it does best, heat water quickly, while avoiding the pitfalls of its inconsistency.
The thermoblock is often put near the group head, providing indirect heating of the brew chamber in addition to heating the water.
How Espresso Machines Heat Water
The original espresso makers used stainless steel boilers heated by open flame, but as time went on they progressed to electric heat. In the 1920s Achille Gaggia invented the lever-operated espresso maker, culminating in the first espresso shot that would satisfy a modern aficionado. His machines used boilers, but instead of steam pressure used a lever-operated, spring-powered piston to drive the water through the grounds. (2)
While lever operated systems have mostly been replaced by pump driven systems, the single boiler heating unit has persisted.
Using a single boiler to produce hot water for both espresso and steaming, these coffee machines require some additional care to use. Some single boiler systems require you to flip a switch when switching between brewing and steaming (3). Forgetting to do so can run overly hot water through the grounds or result in water too cool to generate steam effectively.
Switching modes is relatively quick and easy, usually only taking 25-50 seconds. Just don’t forget!
Heat exchanger systems were developed as a way to overcome the inherent limitations of single boilers. Heat exchanger systems get their name from the fact that the boiler in these systems only directly heats water for the steam side.
The coffee brew water runs through a copper line that is coiled through the heated water. As the water travels along the line it picks up heat from the steam reservoir and comes up to a temperature sufficient for espresso brewing.
Ernesto Valente’s Faema E61 was the first pump driven espresso machine and utilized a heat exchange heating system. It was released in 1961.
Double boiler espresso makers employ two separate heating units: one for steam, and one for coffee. With one boiler dedicated to steam and another to espresso, you never have to worry about a long series of milk drinks lowering your espresso brew temperature.
Many commercial espresso machines – like the ones we mentioned in these post – use double boilers as they churn out consistent espresso shots and steam all day long. See some of the best ones here:
While double boiler systems are great coffee makers, they have several disadvantages. They are bulkier than other heating systems, involve considerable complexity and corresponding cost, have long preheating times, and are not energy efficient as the water is held at temperature constantly.
As a close relative to thermoblocks, thermocoils work on the same principle: a heating element embedded in metal runs alongside a water pipe flash heating the water. While the body of the thermocoil is usually aluminum, the embedded pipe may be a different material such as copper or stainless steel. The main difference between the two technologies is that thermocoils are one piece units, and thus don’t suffer from the leakage problems of thermoblocks.
Some thermocoils are built into the exterior of boilers. These units serve double duty, heating the water in the brew chamber and then directing water from the tank through the serpentine passages in order to create steam. (4)
The primary disadvantage of thermocoils is their cost compared to other thermo heating units.
Thermoblock vs Boiler
- Require less preheating time
- Can generate constant hot water
- Are more energy efficient
- Have better temperature control compared to single boiler systems
- Have worse temperature control compared to double boiler systems
- Are more susceptible to leaking
- Are more heavily impacted by scale
- Have shorter lifespans before needing repair or replacement
Thermoblock vs Thermocoil
- Cost less
- Are equally energy efficient
- Are more susceptible to leaking
Taking Care of Your Thermoblock System
The single biggest danger to thermoblocks is the accumulation of calcium deposits, also known as scale. Some materials such as stainless steel and bronze are less likely to accumulate scale, but no material is immune to the problem. (5)
If your water is hard you are at a greater risk, but even relatively soft water can cause scale accumulation over time. Avoid this by using a water filter. Filters lose their efficacy over time, so change it at the manufacturer’s recommended intervals.
“You need to be mindful of the quality of the water you are putting into your machine...If you are using tap water or you are using a bad filtration system, that is going to destroy your equipment, in addition to making your beverages taste bad.” - Perfect Daily Grind
If you suspect calcium buildup then you’ll want to descale your machine. Your manufacturer will detail the process, and most major manufacturers have their own descaling products that they suggest using.
Thermoblock heating units still have a tendency to leak over time. The heating unit will eventually need to have its gaskets replaced. Depending on your comfort level this may be a DIY project, or might involve sending your unit to a repair company.
- Thermal Block (Boiler) Replacement. (n.d.). Retrieved from https://siber-sonic.com/appliance/800thermalblock.html
- Stamp, J. (2012, June 19). The Long History of the Espresso Machine. Retrieved from https://www.smithsonianmag.com/arts-culture/the-long-history-of-the-espresso-machine-126012814/
- Guerra, A. (2019, July 11). Barista Guide To Buying a Home Espresso Machine. Retrieved from https://www.perfectdailygrind.com/2015/01/the-barista-guide-to-buying-a-home-espresso-machine-2/
- Nascardi, P. (1982). https://patents.google.com/patent/CH632402A5. CH632402A5.
- Espresso Machine Boiler Material Pros and Cons. (n.d.). Retrieved from https://www.espressooutlet.net/espresso-outlet-blog/espresso-machine-boiler-material-pros-and-cons/