Figure 1. Humidifiers are designed to operate in the 35% range. Although 40% to 60% is the optimum zone, most homes will not tolerate wintertime humidity levels in this range for a long period of time without condensation water damage occurring.
The first mistake contractors can make regarding residential humidifiers is to not recommend them to customers in the first place. Most homes around the country could benefit from whole-house humidification. But many contractors zip in and out of a home, fixing whatever problem they’ve been called to fix, without ever mentioning the benefits of a humidifier.

Maybe some contractors are scared of installing a humidifier incorrectly. Or maybe some contractors would just rather not work with water. Maybe it’s just the fear of the unknown. Yes, there are some tricks of the trade, but a discussion with a manufacturer’s representative or even some reading of manufacturer literature can take care of that.

The benefits to a residential humidifier are numerous. It can help protect a home’s furnishings, including hardwood floors and woodwork, which can dry out and warp over time. More importantly, a humidifier can help the home’s occupants feel better, by reducing stuffy noses and improving allergy and asthma symptoms.

The key to being successful with residential humidifiers is to learn how to size, select, and install them correctly.

Figure 2. This chart helps to determine indoor relative humidity (rh). For example, when the outdoor temperature is 10° and outdoor rh is 70%, a home heated to 72° has an indoor humidity level of only 6% — much drier than the 25% rh of the Sahara Desert. Humidifiers can restore a home’s rh to a healthier, more comfortable 30% to 50% range.

Size it correctly

Humidity is a mystery subject to most homeowners and some contractors, notes Hank Gartland, general manager, Walton Labora-tories, Inc., Passaic, NJ.

“It’s difficult to sense relative humidity as opposed to hot or cold air, so it’s hard to explain to the homeowner. So many of us don’t,” he says. “As a result, we hear from homeowners who say they didn’t know that their hvac contractor was the proper person to install a humidifier. Some even say that their contractor ‘doesn’t do’ humidifiers.”

That’s definitely a missed opportunity. Every contractor out there should “do” humidifiers and “do” them correctly, say the experts. Sizing a humidifier is the first step in a proper installation. Too often, contractors undersize humidifiers, so homeowners receive little to no benefit from the units. Gartland notes that it’s important to remember that today’s big houses need big humidifiers. “They should be truly sized like a furnace, so that a certain level of humidity can be ensured at all times, even when the owner is on vacation. You set your thermostat and expect to get what you set.”

Gartland adds that the homeowner should be able to set the humidistat the same way.

“The humidistat needs to be connected to a big enough humidifier to do the job. And don’t make the humidifier a slave to the furnace — wire the humidifier so it can operate whenever it is needed.”

A humidifier is one component of the system that actually should be oversized, says Earl Lewis II, engineering manager, Skuttle Indoor Air Quality Products, Marietta, OH.

“The humidistat will control the humidity level. This isn’t like a refrigeration system or a gas appliance that will be consuming a lot of extra energy,” says Lewis. “You want to oversize the humidifier to satisfy the house for its current conditions plus any additional modifications made to the home.”

When in doubt, check a manufacturer’s catalog. Most have very specific information about how to size a humidifier correctly, including house construction, square footage, heating source, etc.

Select the proper unit

Another problem contractors face when choosing a humidifier for a residential application is determining the type of humidifier to use. There are several different kinds, and they’re meant to be used in different ways. For example, a spray unit shouldn’t be used in an area where there is more than 7 grains of water hardness. That’s going to lead to lots of problems, because calcium will form on the nozzle, causing the unit to drip.

Lewis notes that the humidifier should be chosen based on the type of system as well.

“Heat pumps generally require a different type design than a typical humidifier to be efficient because of the low temperatures of the heat pump. Contractors need to keep those things in mind. And if in doubt, call us. We’re very grateful to talk with people who call and have questions before they install humidifiers.”

Choosing a high-quality humidifier is another important factor. How do you find out about a humidifier’s reputation? Ask around. Wholesalers and other contractors will have definite opinions as to which humidifiers are the best. As Gartland notes, contractors know that one humidifier warranty service call will cancel their profit.

“And they don’t get rich on replacement pads either. So choose quality,” says Gartland.

Proper installation

Many contractors have questions about the proper installation of humidifiers. One of the most common questions is where to mount it — on the return or supply side. For most types of humidifiers, it really doesn’t matter, notes Lewis.

“The furnace has a negative pressure on the return air and a positive pressure on the warm air side. So the result is going to be the air is going to flow from the warm air through the humidifier, whichever side it’s mounted on, and back into the return air.”

As for humidity being lost when it passes through the furnace, this is simply an urban legend, according to Gartland. The heating system is warm, and the only way the moisture can be subtracted out is by condensing on a cold surface. Since the surfaces are all warm, the air is going to be able to absorb even more moisture than it’s currently carrying, so it’s not going to condense on anything. It’s going to be carried on into the home and dispersed throughout, notes Lewis.

Another common question asked by contractors concerns under-duct-type humidifiers (e.g., steam unit, rotating drum, or flow-through under-duct) and on which trunk line should they be placed — the one that goes towards the kitchen and the dining room or the one that goes towards the bedrooms.

“Either one,” answers Lewis. “It doesn’t matter which one you put it on because humidity migrates at over 25 ft per second. It’s like when you walk into a house and somebody has been cooking fish, and you can smell the fish throughout the house. Humidity travels the same way.”

And just think how fast your name will travel amongst your happy customers once you start offering humidifiers — correctly sized, selected, and installed, of course.

Sidebar: Don't forget the maintenance

Every humidifier will require at least occasional maintenance, so don’t put it in a place that will be difficult to service. If it’s hard to reach, it’s almost guaranteed that no maintenance will be performed.

Of course, the ideal situation is to sell a service contract to customers who purchase humidifiers. That way you’re sure that the units are being taken care of properly. And, of course, it adds to the revenue stream.

Contractors should make homeowners familiar with their humidifiers before they ever leave the house. Tell them where the water shut-off is, where the humidistat is, and give them a brief lesson on how to service and clean the humidifier.

Depending on the type of humidifier, contractors should also give customers an idea as to what kind of maintenance schedule they should follow. Of course, that depends on water quality and the type of humidifier installed. After detailing all that information, it’s going to be the rare homeowner who foregoes purchasing a service contract.