A certain amount of humidity makes a living space a lot more comfortable. Too much and you get condensation and mould.

I can tell when it's too dry at my house. I get little splits on the ends of my fingers, and they hurt like the dickens. I also start zapping things after I walk across the carpet -- potentially fatal for my computers.

House humidity comes from many sources -- the shower, cooking, plants, and people. In our house, add a clothesline in the basement and big open kettle on the wood stove.

Our new forced-air natural gas furnace has a humidifier installed. Every year I break down after a while and get the humidifier going on its lowest setting. I suppose this is more energy-efficient as well as being more comfortable, since water vapour holds a lot more heat than air.