'I also have a central humidifier which does a superb job (Craftsman
3000, 14 years old, foam wheel type).'

Being in the Trade, i can tell you that this type of humidifer is the
worst one. WHenever the humidifer wheel is not turning, you have
standing water which is a breeding ground for bacteria , algae, and mold
to form. Then it gets delivered thru your duct system by the furnace
blower to all areas of your house. Just thought id give you a headsup
so you dont get an airborne disease(s). Aprilaire Brand is the best to
have to prevent this entirely.