Why 20% RH when it is 0 degrees outside?

Consumer question:

Why do you use 20 degree relative humidity when outside temperature is around zero? At that level lips crack, nose bleeds, lips crack and dry throat causes coughs. Wood carvings also crack. So while the control panel tells us to set at 20, we are using 40.

Aprilaires’ response:

Thank you for your email regarding your model 700M Aprilaire humidifier. We designed our humidifiers to maintain an indoor relative humidity of 35% anytime the outdoor temperature is 20F or above. The actual amount of humidity a specific home can hold varies. Some homes may be able to hold more humidity than 35% at 20F outdoor temperature. If you are able to maintain 40% humidity without seeing condensation on your windows you may continue to set your control to 40%. Our concern is if you try and maintain too high of a humidity level, the result is damage to your home. The guide lines in our owners manul are to reduce the opportunity for damage to your home while keeping the home comfortable. This is why we recommend maintaining an indoor relative humidity of 25% anytime the outdoor temperature is 0F. As the outdoor temperature drops the indoor air can hold less humidity, so we advise to reduce te humidity set point.

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