Furnace Humidifiers 101

As the outside air becomes cold and dry, so too does the air inside our homes. So how do we achieve a more comfortable environment? By increasing our home’s humidity! Ensuring that you have the right level of humidity in your house can make the cold winter months a lot more comfortable and enjoyable for you and your family. At Carson Dunlop, we are often asked a variety of questions about furnace humidifiers. The most commonly asked questions include:

  •  “Do I need a furnace humidifier?”
  •  “Do I have a furnace humidifier?”
  •  “How do I maintain my humidifier?”

Do I Need a Humidifier?

If your house is new, you may not have a humidifier. However, you may not need one because the foundation and wood framing are still drying out, releasing moisture into the air. In addition, new houses are “tight”, which means the air within them hangs around for a while before being replaced by dry exterior air. The air is around long enough to pick up moisture from things like showers, cooking, drying clothes and breathing. By comparison, older houses are drafty. Cold, dry air is creeping in all the time, drying out the home as it flushes the warm moist air out.

Do I have a Humidifier in My House Already? 

If there is a small box like the one in the picture above hanging from the furnace or ductwork beside the furnace with a small electrical wire and a small water hose attached, you have a humidifier. You may also see a humidistat, a dial that looks like the thermostat but is used to control the humidity level, and is often mounted to the basement ductwork.

The two most common humidifiers include:

1)      Drum Type Humidifiers

A drum type humidifier has a tray of water with a sponge, barrel or drum rotating through it. The tray is kept full of water with a float switch, which allows the water from the plumbing system to enter the tray when the water level drops. When the humidistat is turned up or the humidity level drops, a small electric motor rotates the sponge drum through the tray, absorbing water. Some of the air moving through the ductwork blows across the sponge, picking up moisture. This moist air moves through the ducts and into the rooms.

2)      Trickle (Cascade) Type Humidifiers

Cascade type humidifiers have no tray of water. A small electric valve at the top controls the water supply to the humidifier. When the humidistat calls for water, the valve opens, trickling water down a honeycomb-like metal pad. Air blows across the pad, picking up moisture. Excess water is drained through a hose to a floor drain, laundry tub, or condensate pump.

How Do I Maintain My Humidifier?

If you have a drum type unit, the tray of sitting water is your nemesis. Ponding water can cause scale build-up and bacterial growth. Every spring, the water supply pipe valve should be turned off, the tray and sponge should be cleaned, and the humidistat should be set to OFF. In the fall, turn on the water valve, and set the humidistat to 35%. We recommend a mid-winter cleaning as well.

If you have a cascade type unit, turn off the water supply and turn the humidistat to OFF in the spring. Before use in the fall, remove and soak the pad in a de-scaling solution. If it is damaged or too clogged to clean, the pad can be replaced. Once the pad is back in place, the water supply pipe valve can be turned back on, and the humidistat set to 35%. This unit will not need cleaning again until next year.

How Much is Too Much?

While an ideal humidity for homes can be as low as 5%, people feel the most comfortable in environments with about 60% humidity. Unfortunately, houses can have a hard time coping with this in cold weather. Too little humidity makes people feel uncomfortable. Too much can cause condensation, mold, mildew, and rot in homes as the warm moist air hits cool surfaces. Contrary to common sense, homeowners actually have to LOWER the humidistat setting as the weather outside gets colder. Why? The colder it is outside, the easier it is for condensation to form on cool surfaces like windows. Homeowners can reduce condensation by lowering the interior humidity level. The recommended house humidity levels are:

 Outside  Recommended House Humidity
 -20°F  15%
 -20°F to -10°F  20%
 -10°F to 0°F  25%
 0°F to +10°F  35%
 +10°F and above  40%
 Summer months  Off

Keeping an eye on the amount of condensation on your windows is another great way to gage your house humidity level. In addition, room temperature and humidity monitors available at hardware and building supply stores can also help you manage humidity.

If you want to learn more about your home and enjoyed these tips, order a copy of the Home Reference Book. You can also receive all the latest updates from Carson Dunlop by subscribing to our blog, following us on Twitter or liking us on Facebook.


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