Installing a Whole-House Humidifier

Forced hot-air systems keep you toasty, no question about that. But if the inside of your nose burns, your skin is dry, your eyes are red, and a walk across the carpet zaps you at the light switch · you need a humidifier. A hot-air system can drive your home's relative humidity as low as 10 percent that's twice as dry as the Sahara Desert. Not only is dry air tough on lungs and skin, it's bad for the things you own. It can crack wood furniture, make your books brittle and parch your plants. And it hits you in the pocketbook: since dry air feels colder than moist air, you're more likely to crank up the thermostat.

Well, we rest our case. A whole-house humidifying system is one way to restore a healthy moisture level. Here, we'll look at the best whole-house systems and show you how to pick one that's right for you.

Portable or Whole-House System?
Some portable systems are capable of humidifying your entire house. But while they're simple to use just fill a unit with water, park it near your heating system's return air register and plug it in they have distinct disadvantages. Portable units that are large enough to humidify a house take up valuable floor space. They're loud. They need frequent cleaning. And you have to refill the reservoir by hand every day or two.

Whole-house units are often less expensive than portable humidifiers, and since they connect directly to a water line in your home, they refill automatically. They're quieter and less expensive to run. A whole-house unit takes a little more work to install, but as you'll see, it's not difficult.

Whole-House Choices
There are three major types of whole-house humidifiers:

Drum systems use a foam or fabric belt to move moisture into the air. The belt fits around a drum-shaped frame, which rotates through a water reservoir that wets the belt. When air from your heating system blows across the belt, it carries the moisture into your home. Drum systems are usually the least expensive of the whole-house options. However, they must be cleaned periodically; otherwise, mold may form in the water reservoir, and dust and minerals from your water supply may clog the belt.

Flow-through systems use a rectangular foam or expanded aluminum pad to transfer moisture to the air. Water drips down the pad; the forced air from your heating system flows through the pad, picks up moisture and carries it around your home. Any water that doesn't evaporate is carried away through a drain in the bottom of the unit. Since these units don't have a reservoir of standing water, they don't promote mold growth. However, dirt from the air and sediment and mineral deposits can still clog the pad unless you clean or replace it periodically. Also, you need to have a floor drain to handle the water run-off from these systems.

Spray mist systems don't use a belt or wick. Instead, an electronic mister sprays water vapor into the heated air in your ductwork when the heating system turns on. Again, since there's no standing water, you don't have to worry about mold forming. But these systems won't work with well water or public water supplies that are high in minerals, because impurities and minerals will clog the mist head. Spray misters are only recommended for use with oil-fired and gas-fired heating systems.

A humidifier system may or may not have a fan built into it. Humidifiers that have a fan built in usually mount directly to the supply (hot air) side, as do spray mist systems. Systems that don't have built-in fans typically mount on the cold-air return duct and connect to the supply duct. The strong flow of warm air from the supply duct draws air from the return duct and across the humidifier's drum or pad. The air picks up moisture in the humidifier and then is routed to the supply duct, and from there throughout the house.

Picking a System
When choosing a system, you need to take into account the type of heating system you have and your water's mineral content, for the reasons just noted. Choose a unit that's large enough to handle the square footage of your home.

Two add-on options are well worth considering. A humidistat lets you adjust the percentage of humidity in your home to meet your personal preference. A bypass gate is a good choice if you have a heat pump or central air conditioning. A gate lets you block off the humidifier in the summer, when you don't need to add extra humidity.

Tips From the Pros
Humidity in a home should range between 30 percent and 50 percent. At higher humidity, you'll notice condensation collecting on the windows, and signs of mold and mildew. Much lower and you'll continue to have the symptoms of dry air. If your house is very tight (lots of insulation and no drafts), you may need less humidification per square foot than a house that's not so tight.

Installing a Typical System
How you install a whole-house humidifier varies from system to system and from manufacturer to manufacturer. But there are some common points. To show you the basics, here are the steps involved in connecting a typical fanless drum system with a humidistat and a bypass gate. Note: Never install a humidifier in an area that might freeze. Step by Step

1. Pick a place for the humidifier. In most fanless systems, the humidifier attaches to the cold-air return side of your furnace. To position the unit, find the template supplied with the humidifier installation kit and tape it to the return air ductwork. Use a level to adjust the template, so the humidifier's water reservoir will be level.

2. Mark the screw holes and humidifier opening holes. You'll need four pilot holes for the mounting screws one at each corner plus four holes just inside the corners. Those last four you'll use as corner markers when you cut the opening in the ductwork. Use an awl or other sharp tool to make a small nick in the center of each mark before you drill. (You may want to have a look at our article on drilling tips.)

3. Drill all eight holes. The manufacturer should recommend the bit size for the mounting holes; if not, choose a bit that's slightly smaller than the diameter of threads on the screws you're using. The four holes you'll drill to make the opening will need to be several bit sizes larger than the pilot holes, so you can get the tip of your tin snips into them.

4. Cut the opening for the humidifier. With your tin snips, cut from one opening hole to the next until you have a rectangular opening. Warning: the cut metal will be razor sharp. Wear gloves!

5. Install the humidifier. Use a screwdriver and the screws supplied with the unit to attach the humidifier to the duct.

6. Position the bypass gate. The gate should be positioned about a foot away from the humidifier. You'll need this much distance so the flexible duct that connects the two units doesn't crimp and hamper airflow.

7. Mark and drill the mounting holes and opening holes for the bypass gate. Once the gate is in position, mark the locations of the mounting holes. Then trace around the inside of the collar; this line will serve as your guide for cutting the opening. Drill the mounting holes and then make a hole at the edge of the opening to give you a starting point for the tin snips. Cut out the opening.

8. Install the bypass gate. Use a screwdriver and the screws supplied with the unit to attach the gate to the hot-air duct.

9. Connect the flexible ductwork to the humidifier and the bypass gate. Cut the ductwork to length with a pair of scissors. When the duct is installed, it should span the two units without sagging. Attach it to the humidifier and the gate, using the hose clamps or other fasteners provided.

10. Attach the water supply valve to a copper or CPVC water line. (If you have flexible water lines or galvanized pipe, you'll have to call a pro to install a fitting. Working with flexible lines requires special tools, and galvanized pipe is generally just too thick for the humidifier's connection valve.) First, turn off the water and open a faucet (upstairs, if you have an upstairs) to relieve household water pressure. Measure to the nearest cold-water line and make sure the flexible plastic tubing that came with the kit will reach between the water line and the humidifier. (If not, you'll need to buy additional tubing and a connector.) Typically, you'll use a tap-on fitting, which clamps around the water line and has a valve stem that ends in a sharp point. The point pierces the water line when you turn the valve clockwise. Use a screwdriver and open-end wrench to tighten the clamps so that they hold the valve in place, then turn the valve down to create the hole.

11. Connect the supply tubing between the humidifier and the water supply valve. Cut the supply tubing to length with a utility knife. Attach the supplied compression fittings to each end of the line. Connect the fittings and use an open-end wrench to tighten them.

12. Install the humidistat. Use the supplied template to mark a location on the return duct for the humidistat. It should mount at least 12 inches above the humidifier. Mark the mounting holes and the opening, following the same steps you used for installing the humidifier. Drill the holes and cut the opening. Now attach the wires to the humidistat and screw it in place. (You may want to check out our article on essential wiring skills.)

13. Install the transformer. A transformer reduces regular house current to the lower voltage (usually 24 volts) that runs the humidifier. Locate the closest receptacle, then run the supplied wiring from the humidistat to the transformer. Attach the wiring and plug in the transformer.

Maintenance
To keep your whole-house humidifier in peak shape, you should clean and maintain it at least once a year. The best time is right after the heating season ends, when any minerals and debris in the system are still moist and soft. To clean the unit, make up a 50/50 mixture of white vinegar and tap water. Soak the pad, belt or mist head in the mix for 30 minutes. This should loosen any mineral deposits and dirt so they're easy to wash off. If you have a drum system, apply a few drops of oil to the motor that drives the drum to keep it running smoothly. Leave the system dry and disconnect the power until the next heating season.

Kevin Ireland was formerly managing editor at both American Woodworker magazine and Rodale Woodworking and Do-It-Yourself Books. He was raised in a fixer-upper and has rebuilt three homes in the last 16 years.