I would like to buy a portable humidifier but I am unsure where to place it. I am hoping to buy one that can do the whole job. If I place it on the 1st floor, will it spread to the 2nd floor easily? Or if I place it on the 2nd floor will it spread better to the 1st floor. Or should I just get one for the 1st and 2nd floor?
The humidity in my house is around 25% on both 1st (1,000 sq ft) and 2nd (750 sq ft) floors?
Which portable humdifiers do you recommend? I would like to get an extremely quiet one where I dont have to replace filters.
Your best bet would be to locate a humidifier close to an air return so that the humidified air can be distributed through the house. Take a look around and see what you can find. I don't think you can find a large humidifier without a filter/wick. It is possible though.
You are most likely to find an evaporative type that uses a wick. This may be referred to as a cool mist humidifier. This is going to cool the air in the area where the humidifier is operating. Check out places like Amazon or Epinions for reviews on humidifiers. Also, it looks like the large humidifiers require frequent refilling. That would be once or twice a day.
I would not try to humidify the air in an effort to save energy. It takes 8,500 BTUs to evaporate a gallon of water. To evaporate a gallon of water per hour is 8,500 BTUH. Your furnace will need to make up for the heat lost through the evaporating water. Compare that to your heating system which I would guess has about 64,000 BTUH output.
I would recommend a humidifier if you were doing it for reasons of comfort, health, or concern over wood products.
I have never looked at the numbers I mentioned above until now. It looks like it might be around 5%-15% of your furnace output to humidify the air.