Aprilaire Humidifier Control Eliminates Hassles

Friday, December 11, 2009 by Dennie Plomedahl

A question from Perry in Chicago

"I have a question. I have an old Aprilaire humidifier attached to my home's furnace. There is a dial on it that says either dry (20 or lower) or moist, 40 or higher. So what does this mean? the label says relative humidity, but does that mean the relative humidity outside or inside my house? I live in chicago, and its 0 degrees today and my basement windows have so much moisture on them, that they have iced over! I had the RH dial set to DRY, or 25-30. Help!"

This is a great question, Perry.  From your description, it sounds like you have a manual humidifier control, which means you have to change the setting on your control as the temperature changes outside.  Your home can achieve a higher relative humidity (RH) when the outside temperature is higher without moisture forming on your windows.  However, when the outside temperature drops, like it recently did in the upper midwest, you will form moisture on your windows if you don't dial down the control.

Outside TemperatureRecommended RH
+40F45%
+30F40%
+20F35%
+10F30%
0F25%
-10F20%
-20F15%

As you can see from the table above, at 0 degrees F, the recommended RH is 25%.  However, this can vary from home to home, depending on the level of insulation in the walls, type of windows, how tight your home is, etc.  With the extreme temperatures you are experiencing, your control should be down to almost it's lowest level.

Automatic control removes the hassles
To eliminate the hassle of constantly adjusting your control, I would suggest you call your local Aprilaire dealer and ask him to upgrade you to an Aprilaire automatic digital humidifier control.  It works in conjunction with an outdoor temperature sensor to adjust your indoor RH according to the outside temperature.  After the initial setup, you never have to adjust it again.  We call it the "set it and forget it" control.  The control also tells you your indoor RH, when to change the water panel and if service is required.

Thanks for the question, Perry, and thanks for buying Aprilaire products.

 


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