These details (above and below) from the early patents show some of the parts of Aprilaire’s whole-house humidifier. (U.S. patents 2,637,540 and 2,947,452.)
MADISON, Wis. - Carl Rowe's name is on the U.S. patent issued in 1954 for the first Aprilaire whole-house humidifier. He said he is one of the people involved in creating the breakthrough product; he was in engineering and development for Research Products Corp. at the time.

He wanted something that would help his home feel less dry in the winter. He convinced the president of the company, R.E. Onstead, to add it to the company's existing line of products, which at the time included pads for evaporative coolers.

Ernie Rothe was involved in the initial marketing of the product. "I was an assistant general sales manager at the time," he recalled.

Both he and Rowe feel a strong debt of gratitude to others at the company who have passed on before seeing the product's 50th anniversary this year. They include Onstead and Harry Elwell, vice president of manufacturing at the time the product was introduced.

Elwell also suffered from what Rowe described as "a sensitive nose," and he was easily bothered by dry, overheated winter air. Elwell installed the prototype unit in his own home and turned it on before he came to work. "He said that when he came home that day, water was running down the walls," Rowe recalled wryly. Obviously the product needed to be fine-tuned.

Onstead developed and pushed the concept of "whole-house humidification," Rothe said. "We sold humidification, not humidifiers," he explained.

"This was a key marketing concept." Its impact on the entire HVAC industry has been hugely enduring.

The Catalysts

As mentioned already, one catalyst for the product was Rowe's sinus and skin discomfort and the desire to improve wintertime conditions in his own home. He and Elwell had shared sympathy for each other's plight, and bemoaned the lack of existing products that would help humidify the entire house.

"In my opinion, the world was lacking a good home humidifier," Rowe said. "Controlling indoor humidity in winter-heated homes was not being done well.

"The other catalyst," he continued, "was that we were already making evaporative cooling pads. The technologies [evaporative cooling and whole-house humidification] have a lot in common." Basically, they both use water to saturate a pad to condition very hot air.

Because of its work in evaporative cooling, the company already had a lot of data on air temperature and moisture relationships. In order to fine-tune that weepy prototype, the company used existing information and used its labs to conduct further research.

"We had to get a sound footing on how much water we would need to evaporate," Rowe explained.

Early Changes

There were a few design obstacles to overcome. For instance, "Unless you are in the humidifier business, you don't question whether water will run into a hole," Rowe said. It's funny now, but was frustrating enough at the time.

That first humidifier was made with the paper pad used for evaporative coolers. To overcome the water-run problem, "Chemists on staff worked out a wicking-type coating to facilitate water movement," Rowe said. Today's products use a metal pad with a coating that helps evaporate the right amount of water for the air.

Another significant change made early on involved the first humidifier's controls. Research Products did not make those humidistats; they came from Honeywell out in Minnesota.

Honeywell's location may explain one of the mysteries of the early humidistat. The first sensor's filament was specified to be human hair, but not just hair; blonde hair, Swedish blonde hair - unbleached Swedish blonde hair. Minnesota's population could have filled that product requirement.

(Editor's note: Why unbleached hair? Bleached hair is more porous due to the chemical processing. It would have changed the control's accuracy.)

There were no early product development teams, Rowe recalled. People worked on it whenever they could while working on the company's core products: evap cooling pads and furnace filters, among other things.

More Developments

Jim Enright, who has been with the company several years and has taken the humidifier through several changes, had these comments about the development of Aprilaire's humidifiers:

"Aprilaire introduced the first residential whole-house humidifier in 1954, and has been a leader in the HVAC industry ever since. The first models had a fan which drew air from the supply duct through a water panel and delivered humidified air back into the duct.

"That concept is still used in Aprilaire humidifiers today, but many changes have been made since those early days. In 1962, the housing material was changed from metal to a black phenolic plastic - breakthrough technology at the time. Those ‘Chippewa' Models 110 and 112 were made for 30 years, which is a testament to the quality and durability of the design.

"Also in 1962, the first bypass model humidifiers, Models 220 and 224, were introduced. These models relied on the pressure differential between the supply and return ductwork to draw air through the water panel.

"In 1971, an easy-to-service by-pass humidifier, the Model 440, was unveiled. The first 440s were blue, which was replaced in the early 1980s with the familiar almond color that is still in use today.

"In the early 1990s, the flagships of the Aprilaire line were Models 550 and 560 bypass humidifiers. These models featured compression-molded, glass-filled polyester plastic housings and represented yet another improvement in ease of serviceability. Also in the early 1990s, the easy-to-service Model 760 fan-powered humidifier was introduced. This humidifier was the first to have an injection-molded plastic housing.

"In the past three years, bypass Models 600 and the water-saving Model 400 were introduced. These have a built-in bypass damper and are the easiest to install and service humidifiers on the market."

Summed up Rowe: "I'm very glad the product is in our line. It has done great things for the company."

Sidebar: Whole-House Dehumidifier

MADISON, Wis. - Aprilaire is bringing humidity control full circle with the launch of its whole-house dehumidifier.

"The new whole-house dehumidifier allows contractors to offer homeowners an innovative, effective, and affordable solution to controlling excess moisture due to humidity in their homes," said Robin Pharo, channel manager for Aprilaire. "Homeowners will no longer have to overcool, tolerate uncomfortable damp/musty conditions, or contend with portable dehumidifiers, just to be comfortable and protect their living space."

Portable dehumidifiers only address a small area of the home and can't control the amount of humidity removed from the air. Additionally, there are over 1 million portable dehumidifiers sold each year; this is business and profits that heating and cooling contractors should take advantage of, Pharo said.

The 90-pint-per-day Aprilaire dehumidifier is a whole-house unit that features flexible installation options, automatic control and fan cycling, and an optional ventilation feature for time-based control with outdoor temperature operating limits.

"Whole-house dehumidification will allow homes to maintain the proper levels of humidity and eliminate the possibilities of mold due to high humidity levels," said Lazarus Angulo of Airflo Solutions, Miami. "Homeowners do not realize that a home with a temperature of 70 degrees F and 70-percent humidity will feel like a house that's 80 degrees.

"The majority of homeowners also turn off their air conditioning during the day to save on electricity, and they expect the home to be 70 degrees when they get home," he said. "This leads to a majority of homes becoming saturated with high levels of humidity and heat throughout the day."

For more information, visit or call 800-334-6011.

Publication date: 08/09/2004