Guide to Coffee has an in depth look at heat exchange espresso coffee machines, the benefits, drawbacks and which machine will suit you best
Heat Exchange Espresso Machines
Heat exchange espresso machines are close in capability to dual boiler espresso machines, the concept of a heat exchanger and the reason for it's name is evident when you delve inside and have a look at how they work.
They consist of one large boiler which serves primarily as your steam boiler, that is this boilers only job is to heat water to a high enough temperature to provide you with steam. This leaves something out of the equation - the coffee!! Well heat exchange machines have copper tubing that spirals through the steam boiler - it enters one side and leaves the other on it's way to the brew head.
They are designed so that the water used for brewing is not held in a boiler - unlike a single or dual boiler machine. Instead when you need to brew water is drawn into the machine and taken through the tube in the boiler, it enters cold and is designed to exit at the correct temperature for brewing. This is a very similar concept to some domestic hot water systems in use.
Similarly to the dual boiler, a heat exchanger machine doesn't need to multitask using one boiler - this gives you the flexibility of brewing and steaming simultaneously meaning less time temperature surfing waiting for temperatures to balance out.
Another benefit that some people prefer is the fact that the water used to brew your coffee spends very little time in the machine, this is preferred by some as there is little chance for the water flavour to be tainted by the metal.
Heat exchange machines may (not always) be available in smaller footprint packages than dual boiler machines as well which benefits those who value their kitchen bench space as much as they do a great coffee.
This method of heating your brewing liquid could introduce the question over consistency of the temperature, while these in theory are designed and engineered to give you the correct temperature for brewing it is possible that they may fluctuate more so than that of a dual boiler.
Cost is also a consideration here with most heat exchangers being in the mid $1000's - and thats just the cheap ones. They will commonly cost in excess of $2000- $3000, they are however usually a very quality product for that price.
Who's it For?
Similar demographic to those who may like a dual boiler:
Need to prepare a number of drinks quickly (simultaneous brewing & steaming)
Experienced in or willing to learn how to brew espresso -these are not a foolproof machine
Requires good/quick steaming performance