Heat exchanger machines are the most proven commercial technology, and they've remained popular for home use because they're capable of pulling very temperature stable shots with fantastic steam power for the money. Once we start looking at the heat exchangers with the e61 group heads, they all pull comparable shots, they're all long lasting/maintainable, have a ton of polished stainless steel, and the functional differences become very subtle but aren't just aesthetic (although that's a big part of it). If you've been wondering how to decide between the Profitec Pro 500, Quick Mill Andreja Premium, Rocket Appartamento, etc, you've come to the right place.
All heat exchanger machines will require an occasional brief cooling flush through the group head, because the brew path can over-heat the coffee if the machine has been sitting idle for more than a few minutes. But this process is simple and you have nothing to fear. Walk up to the machine, flip the brew lever up, run the pump for 10 seconds or until the water flow runs smoothly. Then grind, tamp, and pull a great shot. But if you want a simpler experience then we'd recommend you read this consideration set with brings some of our compact temperature controlled single and dual boiler machines into the mix.
If you're limited on counter space and looking for the smallest footprint in a heat exchanger machine, then the 10.5" wide Rocket Appartamento would be our first recommendation. Before this machine came along no one thought this level of steam power was available in such a small package, and it has a very unique visual appeal. One impact of this smaller case means a smaller 2.25 liter reservoir, no brew pressure gauge, and less room to work under the group head and wands.
The Profitec Pro 500 brings some significant improvements to this class of machine. The biggest attraction to Profitec as a brand though has been their German approach to the internals (check out the internal photos on the product page to see what we mean). Everything is laid out with cleanliness and ease of maintenance in mind using simple tools. The boiler is mounted horizontally for better protection of the heating element, and the heating element can be removed using an allen wrench (instead of an impact wrench in the other two). The pressurestat is a beefier Sirai commercial unit, and the way the pump is mounted results in a smoother and quieter sound than most vibration pump machines. Also, it's two liter boiler will have more steam capacity than the Rocket's 1.8 liter and Quick Mill's 1.6 liter, and it's made from stainless steel where the other two are brass. Some people get unique confidence from the clean taste of stainless steel and its resistance to scale build up. The water reservoir is 3 liters like the Quick Mill, and the drip tray has a large 32oz capacity. The Pro 500 looks like a slightly smaller version of the flagship Pro 700 dual boiler and at 11.9" it's less than half an inch wider than the Andreja Premium Evo. We think this machine is one of the strongest values among heat exchangers because off its serviceability and having one of the largest steam boilers. Many machines that cost more can't match the Pro 500 on these points.
The veteran Andreja Premium has the most pedigree with over 10 years of rave reviews, and it's received some subtle internal improvements in the latest Evo version. It's just an inch wider than the Appartamento and this gives it more presence on the counter and easier access to the steam wand and brewing area.