A whole house humidifier or furnace mounted whole house humidifier is just another example of an extremely neglected component of our house - on top of a brick chimney, an attic, and a crawlspace, which fall into the same basket.
If you're not going to maintain it, it's probably a bad idea to get a whole house humidifier. Since it is attached to a forced air heating system that constantly circulates air throughout the house, poor maintenance can create environment attracting mold growth and help reproduce of dust mites.
Properly operating and maintaining a whole house humidifier helps us relieve many physical discomforts associated with cold / dry weather, including respiratory problems and dry skin and lips. It also lowers or completely eliminates static electricity, cosmetic wall trim separations, cracks in finishes, separating hardwood floor boards, etc. The trick is to balance the amount of moisture in your home at such a level which will benefit your health, living environment, and save energy instead of creating conditions which sometimes cause mold or other biological organism growth (excessive moisture could do that). And for proper humidity balancing, you either have to observe and monitor your environment, or purchase an electronic device which will do it for you. In general, the humidity in your house should not exceed 50% (35% - 50% is the most comfortable). Higher levels will usually create condensation on windows, sometimes on walls and ceiling surfaces, or possible mold and mildew growth.
No matter how advanced the whole house humidifier system installed on your property is - it will require regular maintenance because it won't work properly or at all without it. The truth is - I rarely see one properly maintained or even operating at all.
There are basically 5 types of whole house humidifiers:
Flow-Through (bypass) Whole House Humidifiers (passive and fan assisted) - they use a so-called water pad made out of foam, expanded aluminum, and some other materials. The water drips on top of the square pad and the air from the heating system flowing through the pad picks up the water particles and carries them through the air ducts and around the house. The remaining water (whatever wasn't picked up by the air) drains through the base of the whole house humidifier.
A whole house humidifier's water pad has to be replaced once a year before every cold season to perform efficiently and to prevent mold growth. For the homes utilizing private well or other sources with high levels of minerals, cleaning might be required more often.
For every gallon of water evaporated into humidity, Whole House Flow-Through Humidifiers waste between 5-8 gallons down the drain.
Drum Whole House Humidifiers - they have a drum shaped rotating frame (powered by a small, low voltage motor) and a foam or fabric sleeve pulled over it. The bottom section of the drum is always submerged in water which keeps the rotating foam / fabric moist and allows air flowing through the drum to pick up that moisture. The foam / fabric and the water in a small reservoir under the drum require regular maintenance! If you leave that water standing in an unused humidifier (for example during the summer), and then just start the whole house humidifier unit without cleaning it first, I guarantee that you'll be spreading mold spores through the entire house.
Wick Type Whole House Humidifiers - assembled out of a small reservoir and a filter (wick) that absorbs water from it. The entire humidifier is mounted inside the air duct, and in order to inspect it, you have to unscrew the cover plate and remove the entire unit - I don't recommended it, is cheap and easy to install, but that's all.
Spray Mist Whole House Humidifiers - as the name suggests, they spray water mist into the air duct and the mist is picked up by the flow through the air duct. Don't even consider this type if your house's water supply is a private or community well - it will contaminate the spray head immediately. Those are one of the cheapest and easiest to install types out of all the whole house humidifiers.
Steam Whole House Humidifiers - being the most expensive to purchase / install and not that cheap to operate, it consists of advanced technology and complicated designs. Steam whole house humidifier might operate with or independently from your system heat cycle. Whenever the humidity drops below the setting, they will activate your furnace blower and get the humidity to the right level independently from the thermostat settings. One of the known problems associated with this type of the whole house humidifier is that the water distributed with cold air (with operating furnace blower only / no heat) does not completely evaporate. Condensing on the air duct cold walls might sometimes cause bacteria and mold growth. If you like new gadgets and don't mind spending some serious money for it - go ahead - but it sill does require maintenance.
One more type of a Flow - Through type humidifier but this time almost 100% efficient (as claimed by the manufacturer).
Rotary Disc Furnace Mount Whole House Humidifier by Desert Spring: To be honest with you, I can't say much about it except for relaying information from the manufacturer's website, forums, and discussion boards. It sounds great because it is (as claimed by the manufacturer)
the most effective furnace-mount humidifier on the market
100% efficient - 1:1 conversion of water to humidity
uses only 4 Watts/hr of energy
drain-less system - there's no need for a drain in your utility room / furnace location area
very little maintenance with Auto-Flush accessory (you can do it manually every few days, depending on usage, minerals would only need to be removed every month or two in most regions of North America)
never needs filters or pads replacement - uses self cleaning polycarbonate discs (non-absorbent plastic)
As with every product, there are those who love it and hate it.
Whole House Humidifier Maintenance:
Check your humidifier unit visually on a regular basis (it's hard to remember it especially if your whole house humidifier has been mounted in the crawlspace or attic area)
Make sure that there's no water dripping from the whole house humidifier itself and any of its components (water supply line, drain line, shutoff valve, enclosure, area underneath the unit, or furnace itself)
Replace the whole house humidifier water pad / evaporator pad / filter / foam on seasonal basis (or more often if required). Make sure that you re-assemble everything correctly to prevent water leaks
Clean the whole house humidifier components contaminated with mineral deposits after the heating season ends - it will be much easier to do it when everything is still wet and soft. You can use 50/50 vinegar-water solution for heavier contaminated components. Just soak them for 15-30 minutes (or longer if necessary) and that should help with cleaning.
