Heat exchangers, when compared to say dual boilers, contain one sole boiler inside the machine. This boiler is responsible for both brewing your espresso shots and steaming milk for lattes, cappuccinos, etc. Heat exchanging boilers allow the user to brew espresso and steam milk simultaneously as the boiler shares, or exchanges heat, between both functions independently.
Heat exchangers vs. dual boilers
When in the market for a prosumer espresso machine you'll no doubt come across both of these terms. Dual boilers are exactly that - an espresso machine with not one, but two boilers. The boilers in a dual boiler work independently so you'll find them to be much more consistent with virtually zero recoup time in between making drinks.
Compared to a heat exchanger, where you will need to give your machine a small amount of time to rebuild pressure after use, dual boilers are much more efficient. The downside? Dual boilers are on average much more expensive.
But wait, didn't we just say heat exchangers only contain a single boiler? We sure did. So what's the difference?
Single boiler espresso machines are not capable of transferring heat so brewing and steaming simultaneously is not possible on a single boiler espresso machine.
