The amount of humidity required in a home is dependent on acertain extent on the way it is constructed. A well inulated house with vapor barriers in walls,ceilings and slabs and properly fitting storm doors and windows may require only couple of galolons of additional moisture per day to maintain the proper relative humidity. A house of same size but loosely constructed may need five times as much moisture in the same period.
If you home winds up with too much humidity, it can incease the growth rate and spread of a wide variety of molds. It will also greatly accelerate the rotting process of many woods and other structural materials.