Espresso Machine Elements. Heating elements for espresso machines are a little different from those used in other applications. They must do more than heat water quickly; they must do so very efficiently and and maintain very tight temperature control. These goals are achieved in the following ways:
Low Watt Density. Espresso machine elements have more coils and more surface area than comparable elements with similar power ratings. The heat generated per square millimeter of surface area is much lower, which is why there are more of them. Low watt density means that the temperature fluctuations of the surface area of the element between heat and rest conditions are relatively low. This provides more stable temperatures and reduces over-shooting the set point when the pressure stat comes off.
Increased Surface Area. Because water is pretty bad at conducting heat energy, the more water you can expose to the heating surfaces increases the efficiency of the boiler. It also means that just as many calories of heat can be transfered without super heating the element.
Copper Jacket. Because copper conducts heat 20 times more quickly than other alloys. The result is faster response times, better thermal dissipation and more accurate temperature deadbands