Drainless Flow-Thru Humidifier
The term Flow-Thru refers to water trickling through a water panel and out a drain. The Aprilaire 400 series has the water trickle down the water panel an in to a reservoir. The reservoir has a sensor that detects the water level. When more water is needed the solenoid is turned on, and more water trickles down the water panel and refills the reservoir.
The water panel (Stock #45) that is used in the 400 series is different than conventional Flow-Thru models. This water panel is an absorbent paper mesh that can wick up the water from the reservoir. Conventional Flow-Thru models have water panels made of an aluminum mesh with a porous pumice-like coating that absorbs water allowing the water to evaporate but will not wick up water.
Conventional Flow-Thru models flush out minerals when the water trickles down the water panel and out a drain (3 gph). The Aprilaire 400 will have some slime and mineral build-up from standing water. The Aprilaire 400 water panel needs to be replaced more often than conventional water panels (such as Stock #35). Aprilaire recommends replacing the 400 series water panel twice a season.
The model 400 should still have a drain line connected in the event of a malfunction.
The Flow-Thru is an evaporative humidifier and requires hot air. If not using hot air then hot water should be used. We see little humidity gain if our Flow-Thru humidifier is operating with cold air (and cold water). We run our blower on constant to best utilize our electronic air cleaner, but our humidifier is wired to only operate only when there is hot air and works very well.