Humidifiers are required to make up for moisture lost to the outdoors in winter.
So a humidifier is required in a poorly-built house that has a warm air system that forces air out of gaps in ductwork in attics and crawl spaces.
I always thought that the 'cause' of the loss of moisture is NOT due to air being 'forced out' of 'gaps' and such but, instead, the 'incorporation' of dry, cold air being BROUGHT INSIDE (from outside) due to depressurization by the HVAC system. (New homes would pressurize vs. older homes w/'gaps and holes' would depressurize ...) Would you agree or disagree, and why?
Maybe it's just semantics but I don't see how moisture is 'physically lost'. I see it as a moist house that's being dried out due to the incorporaton of dry, cold, winter air ...