Sleeping in the Sauna

Last winter we burned out another humidifier.  We've been running one every night for years because it really seems to reduce the brunette twin's allergy symptoms -- with it she sleeps soundly, without it she is restless. 
Last winter I got tired of buying filters for the cool air humidifiers, so we bought a warm air humidifier.  It adds humidity and heat to the girls' bedroom.  We turned off the humidifier when we turned off the furnace.  The next morning, the brunette twin woke up sounding raspy and sneezing.  The day after she sounded a bit more congested. 
My husband said, "Do we need to turn the humidifier back on even though we're not running the furnace?"  We decided to try it.  The next night she slept soundly and woke up sounding clear -- no congestion, no raspy voice, no sneezing. 
Now we're running the warm air humidifier every night -- furnace, air conditioner, open windows.  We're not sure why, but it works for her, so it works for us.