I know this post is old but I would like to add to this. I agree 100% with Attila's conclusions. Aprilaire and any other plate type humidifiers are for the most part just running water down the drain. I have been in HVAC for 35 years and 1st learned of the humidifier scam when I installed a system for a customer that was very concerned about her grand piano. Aprilaire states that if you want more humidity output you should run your fan on "on". This is completely a waste of energy and water and I knew this going into the project. Knowing that heated air was critical, I built a hot water coil to run with the boiler. This allowed me to have 180° air enter the humidifier. I also had a ducted fan to allow my system to run 24 hours if needed. Problem solve! So I thought. The humidity in the house was terrible. At the time the Aprilaire literature stated an output of somewhere in the area of 18 gallons a day so I was completely confused and believed I had a wiring issue that was shutting the system down when I left the job. I also came up with clocking the water and catching it in a bucket coming out of the drain without any heat or airflow and comparing it with the system operating with heat and air. I could not believe that there was virtually no difference. I think the output was well under 1 gallon per day. I didn't waste time changing the pad but instead cut a hole in the front of the humidifier so I could watch the water. The humidifier was perfectly level but the pad was not getting wet because the water would only trickle in a few spots down the honeycomb before running down the drain. I messed with the top to try and get the water to flow evenly over the plate but no matter what I did the water would just trickle somewhere else. I waste many hours at my shop at night trying to understand why "My" install didn't work. The new ones have a material on top to help wick the water but it's basically the same. The pads also have clay on them to help attract the water. I called Aprilaire many times and they said they had never had any trouble.....until on one call to technical service I was lucky enough to get an old engineer who opened up and explained that in the "old days" they worked fine. Back then before water conservation, the humidifiers did not slow down the flow and the water splashed and swirled down the pad in a waterfall. The feel good/cheap solution to put a small restrictor orafice in the water line replaced the waterfall with a trickle. Anyone who stood next to a waterfall and then a creek has felt the difference. With that knowledge, I solved my project by building a pump with a flush system to bring back the waterfall. That was 10 years ago and I can still output 24 gallons a day! I imagine it's better than the old factory numbers because I'm recirculating the water which keeps water temperature up. I stopped installing those humidifiers but all the other companies are making a fortune installing the "water wasters". I did find a huimdifier from Canada that has a rotating drum. They solved the stagnant water issue by adding a flush system to the drain that pumps out the water every 12 or 24 hours. http://www.desertspringproducts.com/...ring/index.asp Their float system stinks but it works. As for the "old engineer". I tried calling him back after I got the system working to thank him but he was no longer there. I'm guessing he was retiring and heard my frustration. Thanks sir, where ever you are.