Single boiler

An espresso machine architecture with a single boiler used for both brewing and steaming. The boiler heats to brew temperature for shots, then switches to a higher temperature for steaming.

Why it matters — Simplest, most compact architecture — common in entry-level home machines (Gaggia Classic, Rancilio Silvia). The trade-off is that you can't brew and steam simultaneously; the machine has to switch modes and wait for the temperature to rise.

Good to know

• For someone making one or two coffees in a row, single boiler is genuinely fine. Pull the shot, then steam.
• The mode-switching wait time is the main reason households making multiple milk drinks usually upgrade to HX or dual boiler.