I am visiting a customer tomorrow that has a humidity problem in their home. we installed an aprilaire 600 on an upflow lennox 80% with dual fuel and a signature stat last summer.
the stat tells them the setpoint for humidity is 45% but house humidity will not go above 30%, sq footage well within limitations of humidifier.
i have been up there once so far,(70 miles north) and replaced and shortened the bypass duct (flex) which had water in it. the system has an aprilaire 5000, BTW, which i am going to "upgrade" having been unplugged on my last visit.
i plan to change the bypass to metal, and wonder if connecting it right into the side of the furnace blower compartment opposite of the return plenum (not going through the filter again) might help. a much shorter run will be used and hopefully will get the moisture into the home.
humidifier is running properly, i have checked it out pretty thoroughly, yet am open to suggestions.