Air is the enemy in a hydronic (hot-water) heating system. It blocks their flow to the radiators. It rattles around and annoys customers. It wastes fuel by making our systems less efficient (no heat from an air-bound radiator). It causes callbacks and it makes us look bad. That’s why every hydronic system needs a good air separator. I think the best spot for this device is on the supply of the boiler. That’s where the water is hottest, and hot water has a tough time holding air. Any air separator, properly installed, will eventually get rid of the air. I like the micro-bubble air separators because they do a brilliant job of getting rid of the tiniest bubbles quickly. Ever draw water from a tap into a glass and then gag because they water looks milky white? Those are micro-bubbles. Let the water settle for a while and it will get clear.