Thermoblock
A compact heating system that heats water on demand as it passes through, used in many small espresso machines.
A thermoblock heats a small amount of water quickly as it flows, so the machine is ready fast and stays compact. It is common in affordable, small-footprint machines.
It heats up quickly but can be less temperature-stable than a boiler, especially when switching between brewing and steaming.
Why it matters for small spaces
Thermoblock machines are usually the smallest and quickest to warm up, which suits flats and occasional use.