How Do I Raise Relative Humidity?

As winter approaches, hardwood households throughout the northern hemisphere are starting to think about how to prepare for the coming months.  With temperatures cooling, outside air can hold less and less moisture, and when that already dry air gets pulled inside and heated, the relative humidity (RH) within your home can drop to dangerous levels—for your health and your woodwork.

By now, you are probably aware of the adverse effects of dry winter air.  Chapped lips, cracked skin, worsened asthma symptoms and respiratory infections become more frequent as the dry air takes its toll on your body.  Static electricity generates annoying shocks, crazy hair and unexpected appendages to your clothing. The plants start to shrivel, the wood starts to crack, and unsightly gaps appear in your hardwood floors, and the air sucks the moisture out of organic materials to make up for its deficit.

Fortunately, there are some things you can do, from temporary, localized fixes to long-term, whole-house alterations to combat the dry winter air and reclaim your health and comfort.

Plants

If the RH in your home is just a little low in certain places, you may find that items already in your house are all you need to bring a room back to comfortable levels.

  • If you have houseplants, find a mister or spray bottle and mist the plants every day; this will help them to get the added moisture they need (plants typically like about 10% more moisture than people and wood) and will add a small amount of moisture to the ambient air.  Some people also use a spray bottle to spritz a light mist throughout a dry room, but this requires that the mist be fine enough and in a small enough volume that the moisture does not settle onto floors and furniture.  We think this seems a bit labor-intensive, not to mention risky for your hardwood.
  • Another quick fix often used by folks with plants is to fill a shallow tray with small, decorative stones or pebbles and fill the tray about halfway with water, leaving the tops of the rocks exposed; this will allow for slow evaporation throughout the day and the basin can double as a tray to catch extra water from houseplants.  Depending on what they are made of, you can also set these trays near heat sources or in sunny windows, to encourage evaporation.  Of course, this method requires some maintenance, as you will need to refill the tray regularly and you will want to wash the stones from time to time to prevent mold.
  • Plants, in general, can also help to increase the RH in a room, as there is bound to be some excess moisture at each watering.  You will naturally want to take care that pots are not placed directly on wood floors or in areas where watering is likely to cause drips or overflow that could cause damage.

Around the house

Certain daily activities naturally generate large amounts of humidity.  Small adjustments can make these activities work to your advantage, and cut down on energy costs to boot.

  • If you have space, consider setting your clean clothes out to dry on racks rather than tossing them in the dryer.  As they dry, that pure, fresh-smelling moisture will be directly absorbed into the surrounding air, leaving clothes dry and air moist, at least for a time.  If you don’t want to wait, you can even use a fan to help speed up the process—the result will be the same.
  • A similar principle applies to the dishwasher.  Most modern dishwashers allow you to stop the machine at the end of the wash cycle and air dry rather than bake drying the dishes.  If you open the dishwasher door for the drying process, all of that warm, moist air can escape into the dry air in your home.  Because the dishes will be hot from washing, they will usually dry reasonably quickly and without spots, just as though you had baked them, but the valuable moisture will raise the air quality in your home instead of getting siphoned off outside, where it is not needed.
  • Like a steaming hot shower to push out the cold winter?  Your house might like it, too.  Instead of clearing the bathroom with a vented fan after a shower, try opening the door and letting the moist air blend with the drier air in the hall or bedroom.

Single-room humidifiers

Room humidifiers are just what they sound like—humidifiers, usually reasonably portable, designed to raise the amount of moisture in the air of a single room (about 12’x12’ with a 10’-12’ ceiling).   They come in several varieties and are usually quite affordable, with decent models starting at $30-40, though the fancier ones, which can, for example, be set to operate automatically depending on RH levels, can be as much as $1,000 or more. That’s why many people opt in for humidifier and air purifier combo units to get the best of both functionalities.

  • Ultrasonic, or cool mist humidifiers, are currently among the most popular options for adding moisture to a room and are generally recommended for families because they do not involve any heating implement or steam that could cause injury to a curious child.  In an ultrasonic humidifier, a small metal diaphragm vibrating at ultrasonic frequency breaks water into tiny water droplets that are then blown by a fan into the air.  Though the water in these humidifiers must be changed frequently to avoid microorganism growth, they are quieter than some other types of humidifiers and use only a little electricity.  An alternative to the ultrasonic is an impeller humidifier which uses a rotating disc to fling water at a diffuser that, in turn, breaks the water into minute droplets that then diffuse into the air, for a similar effect.  Distilled water is recommended for either style, as tap water tends to be rich in minerals that can create unwelcome deposits after a time.
  • Vaporizers, or warm mist humidifiers, are essentially steam machines.  They consist of a reservoir of water and a mechanism for heating the water to its gaseous form, which then takes its natural course into the air.  Vaporizers are often the humidifier of choice because the heating process kills many microorganisms that might otherwise be released into the air and the steam leaves behind heavy minerals that could, over the long term, leave residue around the room.  They are also nice for combating winter-time respiratory infections and can be enhanced with medicated inhalants and natural essences to improve respiratory health.  On the other hand, a vaporizer requires a heating device, which always poses a risk of injury and fire (though these are usually minimal) and entails somewhat higher energy usage.
  • Evaporative humidifiers are the most basic of the single-room machines, and work on the same principles as some of the quick fixes described above, though they are, of course, more consistent.  These simple mechanisms draw water from a reservoir in no small wicking surface from which the water can evaporate.  The fan then blows air onto the surface to encourage evaporation. Evaporative humidifiers are relatively inexpensive and easy to use, and these humidifiers can typically cover larger areas than other styles of room humidifiers.

Whole house humidifiers

As you might guess, there are also humidifiers that can be connected directly to your forced air heating and cooling system, so you can use your existing ductwork to raise relative humidity throughout your home.  Like room-style devices, whole-house apparatus work in a variety of ways.

  • Drum humidifiers are one of the more cost-effective whole-house humidifiers to install and maintain.  Inside the unit, a rotating evaporator pad called a drum wicks water from a pan and moved it into the air stream of your heating system, which evaporates the water then carries the moisture as air circulates. The container is automatically refilled from a pipe in much the same manner as a toilet tank. You will need to replace the pad of a drum humidifier regularly, and the pan cleaned from time to time to prevent mold and mildew, but the system itself will run automatically, activated and deactivated by a humidistat, which monitors your home’s relative humidity.
  • Disc wheel humidifiers operate in much the same way as drum models, only instead of a sponge-like pad, a group of plastic, grooved discs carry the water into the air stream; this can be preferable because the plastic resists mold and does not need to be replaced very often, and the output is somewhat higher because of increased surface space for evaporation.
  • Bypass flow-through humidifiers use fresh water rather than a water reservoir as their water source, eliminating the need for frequent cleaning that a standing-water pan entails.  With these units, an electronically controlled valve opens when the humidity drops below a certain point, causing fresh water to flow across a porous aluminum and ceramic evaporator pad.  The pad is placed, so that warm, dry air is forced through it by the furnace blower, evaporating the water, which it carries with it as it circulates throughout the house.
  • Spray, or mist, whole-house humidifiers, like the drum and disc-wheel styles, are activated by a humidistat.  As its name would suggest, the unit releases a fine mist of fresh water into the heating system’s ductwork, which distributes it evenly throughout the home.  Often smaller in size, spray models can fit in spaces where other styles are not an option.  And, because it has no water pan, maintenance for a spray unit is relatively low, though spray nozzles (custom sized according to the volume of air in your home) can get clogged by hard water deposits.