Differential pressure is used with Aprilaire bypass humidifiers, correct?

Consumer question:

Quick question on the install- I have a 7 year old furnace (so it\’s fairly new) and see your instructions say it’s alright to install my Model 600 bypass humidifier on either the return or supply, with the bypass ductwork going to whichever side I didn’t install the panel itself on. Is there any advantage to one side or the other? I would have thought it would be better to have the water panel on the supply side. Also, does it matter whether I use hot water or cold? Opinions seem to be strong both ways.

Aprilaires’ response:

Thank you for contacting us regarding the model 600. A bypass humidifier gets its air movement through the Water Panel® by the differential pressure between the supply (hot air) plenum and the return (cold air) duct. The supply plenum is under positive pressure and the return duct is under negative pressure. One of the advantages of a bypass humidifier is that it can be installed either on the supply plenum or on the return duct with equal effectiveness. No matter which duct the unit is mounted on, the airflow always goes from the supply to the return through the humidifier.

A bypass humidifier will also have no adverse effect on any component in the furnace, air cleaner or filter. Aprilaire® Humidifiers put “water vapor” into the air, not raw water. This is nature’s way of getting relative humidity into the air.

Additionally, the Aprilaire published capacities on our literature are based on the humidifier using cold water, but there are many cases where you may want to boost the capacities of the humidifier. There are no detrimental effects in using hot water on our humidifiers.

There is no additional cost to you when using hot water either. Heat is required to evaporate water. It doesn’t matter if that heat comes from the warm air of your furnace or hot water. If hot water is used to supplement the warm air, it simply increases the capacity of the humidifier. This added capacity will satisfy the humidistat quicker, reducing the amount of time the humidifier runs. This results in less water used.

If you have any further questions regarding this or any of our products, please feel free to contact our customer service department at your earliest convenience.

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