By Mike McClintock
Special to Tribune Newspapers
December 13, 2012
Heating and cooling systems are designed to provide a comfortable indoor environment of 65 to 70 degrees and 30 to 50 percent relative humidity. The temperature is straightforward; just move the thermostat up or down. The humidity is more complicated, particularly with dry winter air.
When the temperature drops below freezing outside and your thermostat reads 70, relative humidity indoors can sink below 10 percent. For people, that's dry enough to chafe skin and trigger coughing. For houses, that's dry enough to open trim joints and produce potent shocks from static electricity. The solution: add moisture.
How much humidity?
More is better, up to a point. The Environmental Protection Agency recommends a limit of 50 percent, mainly to avoid conditions that could breed bacteria. To measure the level, some humidifiers come with a built-in hygrometer, or you can buy a basic one for about $15. But a common-sense rule works as well as the numbers. Add as much moisture as you can without creating maintenance problems due to condensation, like sweating windows and water pipes. When that happens, dial down the humidifier until condensation disappears.
You also want more humidity because warm air feels warmer if it's moist. That allows you to turn down the thermostat. This will eventually cover the cost of humidifying the house and save on repairs due to dryness.
Portables plug in anywhere to take the dry edge off a room — for a while. Larger models that hold more water are sometimes disguised as end tables to blend in. There's no hiding the noise, but the main drawback is you have to keep refilling them.
The limitation for portables is humidifier size: how much water it holds listed as gallon capacity. Humidifier output is specified as the number of gallons delivered per day for a given room size. To get a handle on refill frequency, you need to look at both ratings. For instance, a unit with a capacity of 2.5 gallons and an output of 5 gallons per day will run out of water in 12 hours.
But portables are the only option if your home doesn't have whole-house ductwork. Most do, which allows the best option: a central-system humidifier that adds moisture to air flowing from registers.
Some use a paddle wheel with sponges, like an old water mill. At the bottom of the cycle, sponges dip through a water tank, and at the top release moisture into warm air pushed by the furnace blower. The limiting factor is hard water that eventually cakes the sponges with mineral deposits. Then the pads won't draw up much water. Flow-through systems trickle a stream of water over a wide filter that removes mineral deposits and other impurities. If the filter clogs, some moisture still will be drawn into the supply ducts.
But any type of central system provides several advantages. It controls moisture everywhere with a humidistat at the furnace where it's installed. There's no noisy appliance in living spaces, and no added noise at the furnace because it uses the blower that's pushing air in any case. Better still, central-system humidifiers are connected to the plumbing system and refill automatically.
Start by cleaning or replacing the filter or moisture transfer medium (sponge pad) after shutting off the electrical supply. It's also wise to disinfect the holding tank so fresh water isn't contaminated by impurities left behind last year. Procedures vary, so follow manufacturer's instructions. Mineral scale often needs scrubbing, while a 50-50 solution of bleach and water works for general cleaning. For impeller and ultrasonic machines, the EPA reports, "Only rigorous, daily and end-of-season cleaning regimens, coupled with disinfection, have been shown to be effective." On a central system, annual cleaning and disinfecting is normally adequate.