If you’re in the market for an home espresso machine, one of the first decisions you’ll need to make is whether to select a single boiler or double (or “dual”) boiler model. Just as it sounds, some machines have a single boiler, while others add a second boiler - but why? Let’s examine how this decision affects speed, quality, convenience, and accuracy when making espresso at home.
What’s a boiler, anyway?
A boiler is simply a container for water, heated up and held at the specific temperature needed to make espresso (or steam milk.) We need a steady, consistent supply of water at just the right temperature, and the boiler(s) keep it ready for on-demand use. The machine uses electricity to perform this function.
Single boiler espresso machines - the pros and cons
With a single boiler design, one boiler is shared and handles both the brewing and steaming tasks. The single boiler design is sometimes referred to as “SBDU (single boiler, dual use)”, indicating that the single boiler performs both the brewing and steaming functions.
The #1 advantage of a single boiler espresso machine is lower cost, an important consideration for those just starting out or shopping for their first home machine. Single boiler models have fewer parts and are easier to manufacture, due to their reduced complexity. As a result, many of the lower priced espresso machines you’ll encounter for home use will be the single boiler type and they might be described as “entry level” - although they can still produce excellent espresso.
The #1 downside of a single boiler espresso machine is the time needed to switch between steaming and brewing. The temperature needed for these two processes isn’t the same. That means you may spend some time waiting for a single boiler machine to reach the correct temperature for the task - maybe no big deal if you’re just making a single drink for yourself, but a drag if you’re handling barista duties for a party or large gathering. The wait time depends on the specific design of the machine you select.
To minimize that time, sometimes single boiler espresso machines use smaller boilers to help speed up the process - it’s faster because there is less volume of water to heat and hold at temperature. However, that means they can’t repeatedly make beverages, back-to-back, without waiting in between for the one boiler to fill and come back to the correct temperature. This might not be a big deal if you rarely host guests and tend to make a single drink at a time, but definitely slows down the ability to make multiple drinks in a short time span.
Single boiler espresso machines do have some other benefits that might be less obvious: they’re more economical to operate, because there is only one boiler to heat, and therefore less electricity is used. There are also fewer parts, which means single boiler espresso machines take up less physical room, which can be nice for those with small apartments or limited countertop space. An argument can also be presented that single boiler machines could be more reliable and need servicing less frequently, since there are 50% fewer boilers to maintain.
Let’s summarize:
- Single boiler espresso machines are the lowest cost option.
- Machines with smaller boilers can have faster warm-up times.
- They take up less physical space.
- Operating a single boiler espresso machine can be slower, especially when making multiple drinks.
- If you plan to steam milk, you’ll need to allow time for the temperature of the single boiler to adjust back and forth when you switch between the brewing and steaming functions.
Pros and cons of double boiler espresso machines
Double (or dual) boiler espresso machines use separate boilers for brewing and steaming, one for each task. A key benefit of this design is faster, improved workflow - for example, you can start steaming milk while pulling a shot. There’s no wait time for the temperature to adjust when you switch between brewing and steaming functions, as with a single boiler system.
A dual boiler machine gives you more precise control over temperature. While many enthusiasts prefer this extra level of control, it also adds complexity and expense, so double boiler models cost more than their single boiler counterparts. Another possible con with a dual boiler machine is increased maintenance and service, since each boiler is a potential point of failure and adds complexity to the machine.
In summary:
- Double boiler expresso machines offer a faster, improved workflow, especially if you plan to steam milk.
- But they’re larger, taking up more space, and are more expensive compared with single boiler machines.
- They also use more electricity, since there are two boilers to heat.
- Double boiler designs are probably a better choice if you often make multiple drinks for family or larger gatherings.
What about Heat Exchanger models?
Heat exchanger models (you might see them abbreviated “HX”) are sort of a hybrid between the single and dual boiler option. On an espresso machine equipped with a heat exchanger, a single boiler heats water to the boiling point, so there’s always steam available. But that water is too hot for brewing… so a heat exchanger machine introduces cold water, mixing it with the boiling water, to lower the temperature to the level needed for brewing. Without the complexity of two boilers, heat exchanger machines can cost less in comparison.
Since temperature is critical when preparing espresso and/or steaming milk, the heat exchanger process must be highly accurate, of course, which adds some complexity. Better heat exchanger models allow the user to pre-select their desired temperatures, and always provide the perfect brewing temperature. Less sophisticated heat exchanger models may not allow the user to control the exact temperature, but instead brew in a pre-established range. Generally, this works fine, but may not satisfy more advanced baristas who want very fine-grained temperature control to dial in their espresso.
Let’s summarize heat exchanger pros and cons:
- Can be compact in design.
- Less expensive than dual boiler machines.
- As with single boiler models, heat exchanger models can use less electricity, since there is only one boiler to heat.
- Provides some of the advantage of dual boiler machines.
Key factor - do you plan to steam milk?
Whether you’ll be steaming milk at home on a regular basis is an important factor to consider before making a decision. While many home espresso users will want to steam milk for a latte or cappuccino on a regular basis, some will not. If you won’t be streaming milk frequently and only care about espresso, a dual boiler machine may be much less important for your needs - a less expensive single boiler setup may fit the bill.
If you steam milk regularly, with a single boiler machine you’ll need to wait for the machine to come up to steam temperature after brewing. That may be an acceptable trade-off when you typically prepare a single drink at a time, but can be inconvenient when you’re making multiple drinks in a single session.
