HUMIDIFIERS

Forced air furnaces for homes generally use two basic kinds of humidifiers.

One kind of humidifier is a bypass humidifier. This humidifier is generally mounted on the supply air plenum or main duct off of the top of the furnace. A round pipe goes from the humidifier to the return air duct. The reason that this humidifier is called a bypass humidifier is because a considerable amount of air is bypassed from the supply duct to the return air duct. In other words the air goes from the supply duct through the humidifier pad, and then back to the return air duct through the round pipe. The moist air that came out of the humidifier goes into the return air duct and through the furnace. This type of humidifier humidifies well. There is a damper on the round duct that should be closed in the summer during the air conditioning season. If you have air flow that is marginal, a bypass humidifier will cause a small problem to become larger. If your system has plenty of air flow, then a bypass humidifier will work fine.

View of bypass type humidifier with round galvanized duct that attaches to the return air duct of the furnace. Damper closed.	View of bypass type humidifier

A power humidifier has a small fan that is built into the humidifier. This kind of humidifier is also mounted on the supply air plenum. The fan pulls air from the plenum and through the pad of the humidifier. The fan then pushes the moist air back into the supply air plenum. If you have marginal air flow in your ductwork this type of humidifier is the better choice.

View of power humidifier that has a motor and fan

It is generally preferred to connect the water supply to un-softened water because soft water is more corrosive and will corrode parts in the humidifier faster.