EXPERIENCES WITH HUMIDIFIERS Everyone who lives where winters are cold is familiar with the problem of arid indoor air. When your lips crack and your skin turns to parchment, you don't need a hygrometer to know your plants are suffering too. In my Indianapolis apartment, I have solved this problem by using evaporative humidifiers. These work well, but require more maintenance and accessory equipment than you might think. An "evaporative" humidifer does not use heat or produce mist. It uses a fan to draw air through a paper latticework pad that is kept sopping wet by having its lower half immersed in water. The air comes out the other side humid. You cannot regulate how humid, but the fan has 3 speeds. Humidifiers that use a rotating belt work essentially the same way. These are very effective, if you get a large enough unit or enough of them. Buy more capacity than the box specs say you need. Supposedly, my 8-gallon-per-day unit will humidify 1920 square feet. But few houses are tightly insulated. In practice, there is no way this unit would handle 1920 square feet. I have two of them in my 800 square foot apartment. This is more than needed, but not a lot more. With two, I don't have to refill them as often, can keep them set on low so they're quiet, and can put them in different rooms so no area gets too dry. Each unit cost $85. Of course, I justified this expense by pretending it was for my health, instead of for the plants :-). The result is wonderful. The balmy moisture is quite noticeable when you come in the door, and the plants get adequate humidity in the open, without sheets of plastic or stagnant air. But every solution causes new problems. First, you must add a bactericide to the water every time you refill the humidifier (which is every two days), to keep mold and bacteria from growing on the paper latticework pads inside. (Department stores, hardware stores, and appliance stores carry chemicals for humidifiers.) Second, most houses are dusty; dust soon accumulates on the latticework pads and clogs them. Keeping these pads meticulously free of any crud is crucial to having the humidifier work properly. Initially, I solved this by taping cut-out pieces of that blue spun fiberglass furnace air filter material over all the air entrances to the humidifiers. When it got dirty, I would strip it off, discard it, and tape on new pieces. This is a pain, but less of a pain than cleaning the pads, and needs doing far less often. But now I feel that this furnace filter material is not safe to cut up. Little snips of fiberglas stick into ones skin and hurt. I also worry that bits could be inhaled. But I have been unable to find an alternative. The 3M #9818 "hammock" air filter for furnaces is too dense - the humidifier fan is not strong enough to pull air through it, even when it's clean. If you know of any functional alternative air filter materials, please email me! One would expect that the humidifier manufacturers would produce a complete, working product - including an air filter designed for the fan, or a fan strong enough to work with an air filter. But so far as I know, none do. I've never seen a humidifier that would work as designed. My explanation for this is that most of their consumers have no clue how to use a humidifier, nor how to tell whether it's working or not. This is not a product that you can just plug in and use without understanding it. Certainly most humidifiers I've seen in use were pathetically inadequate for the space they were supposed to be humidifying. Probably the people who bought them just assumed they must be working and couldn't tell the difference. Or if they could, they didn't want to go to the trouble of figuring out how to fix the problem. I also think the manufacturers aren't up front in describing how much humidifying power is needed to really change the humidity in most household environments. If they were, many of their customers might decide it too much trouble. The manufacturers say not to clean the humidifier pads, but they're wrong; you can do so by immersing them in vinegar. This takes a lot of vinegar and a deep, clean container. I then rinse off the vinegar in successive baths of distilled water. The pads must be cleaned about every 6 weeks, and replaced once or twice a winter. I have plastic bins and buckets dedicated to cleaning pads and filling humidifiers. The biggest headache is hard water. If you have hard water, it will clog the pads with lime within a week. There is a chemical, sold as "humidifier water treatment", which claims to "prevent lime scale buildup". However, it is my understanding that this only works for humidifiers that use a rotating belt which is continually reimmersed in the water. It makes the lime more soluble so it washes back off the belt. But with evaporative pads, all salts, no matter how soluble, will end up on the pad when the water containing them evaporates. So I do not believe this chemical is of any use in this type of humidifier. What you would need is something that precipitates the lime out of the water into a sludge on the bottom. If anyone is aware how to do this safely and successfully, I would like to know. I would imagine it involves some nasty acids. The most feasible solution to hard water for evaporative humidifiers is to fill them with only distilled or reverse osmosis water. (RO water is nearly the same as distilled - both have all the minerals removed.) Many supermarkets have "water machines" that vend reverse osmosis water. (Make sure it really is RO and not just filtered, which still has minerals in it.) Twice a week, I was filling four 5-gallon plastic jugs at the store and carrying them home up two flights of stairs. At this point it was cheaper to buy my own reverse osmosis unit ($200). It's well known that RO water is healthier to drink. :-) Even more important, RO water is great for watering plants that dislike lime. There is one unsolvable problem: the degree of humidity that would be ideal for your plants is too much for your house. The moist air condenses on cold window frames; you can even get water dripping down the walls. Then you must lower the humidity to prevent damage to the building. This problem gets worse the colder it gets outside and the less well insulated the house is. Examples: Temp outdoors Highest indoor humidity safe for house less than -20 20% (relative humidity) -20 to -10 F 25% 0 to 10 F 35% 20 to 40 F 40% (From an experiment at U. of Minnesota, as printed in Horticulture magazine; don't have date). (A friend adds: If you have any water condensing on the walls, you are already in big trouble. The water vapor diffuses out through the drywall, and condenses in the insulation. This reduces its ability to insulate, so the wall gets cooler; then even more water condenses inside it. Then the dampness inside the walls makes the wooden studs rot. That is what the guidelines above are supposed to prevent.) Despite these hassles, having a decent humidity level in winter is well worth it. To further improve the situation, you would have to either build a greenhouse or move to a better climate.