Capacity is high because an average-size home (10,000 cu. ft.) requires the addition of approximately 9 gallons of water per day to maintain 35% relative humidity when the outside temperature is 20°. The smallest Aprilaire Humidifier under most operating conditions, has this humidifying capacity. Trouble-free performance and minimum maintenance are assured by the design features of the Aprilaire Humidifier. All unit housing parts that come in contact with water are non-metal and will never rust or corrode. Neither heat nor water will affect them under normal operating conditions.

The Water Panel® evaporator, designed especially for uniform, high evaporation, along with the Scale Control Insert efficiently traps mineral deposits which are often the cause of damage to working parts in ordinary humidifiers. No “white dust” can be distributed throughout the living quarters. The Water Panel evaporator is the heart of the unit and must be in good condition to assure high capacity trouble-free performance. It should be changed once a year with the exception of the Model 400 where it should be changed twice a heating season.

Older design water distribution trays have a granular coating in the bottom of the distribution tray to provide equal distribution of water to each of the openings assuring an even flow over the Water Panel evaporator. Do not clean the mineral scale off the bottom of the water distribution tray at the end of the humidification season. If the granular coating is removed, it is not necessary to purchase a new distribution tray. You can accomplish the same uniform performance by applying a small amount of liquid dishwashing detergent over the entire inside surface of the water distribution tray. This will allow the water to flow evenly through each of the openings, provided, of course, the unit is level in order to achieve maximum capacity.

The current distribution tray which incorporates a synthetic fabric liner that replaces the granular coating, is designed to deliver water uniformly over the entire top surface of the Water Panel evaporator, provided it is mounted level. It is normal for some mineral deposits to form in the distribution tray as it dries out between humidification cycles. These deposits can actually help distribute water in the tray, but if they form enough to block the openings, they should be removed as described in the “Periodic Preventative Maintenance” section of this manual.

There are many humidifiers on the market. They all add moisture… with varying degrees of efficiency. None, however, can provide the features, design, and performance incorporated into your Aprilaire Humidifier.

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Aprilaire 400 owner manual
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400 specifications

The Aprilaire 400 is a high-performance whole-home humidifier designed to enhance indoor air quality and provide superior comfort throughout your living spaces. As part of the Aprilaire family, known for their commitment to creating healthier environments, this model stands out due to its innovative features and advanced technologies.

One of the main characteristics of the Aprilaire 400 is its capacity to humidify homes effectively, covering an area of up to 4,000 square feet. This makes it ideal for large living spaces, ensuring that every room benefits from balanced humidity levels. The humidifier operates seamlessly with the home’s existing heating and cooling systems, requiring no additional maintenance, making it a hassle-free solution for homeowners.

A prominent feature of the Aprilaire 400 is its self-regulating technology. This unit uses a built-in humidistat that senses the moisture levels in your home and adjusts the humidification output accordingly. This ensures optimal humidity—typically between 30% and 50%—which can help reduce issues related to dry air, such as dry skin, irritated sinuses, and static electricity.

Another key benefit of the Aprilaire 400 is its evaporative design, which utilizes a water panel rather than a traditional water tank. This allows for efficient moisture dispersion, as the humidifier draws in dry air, passes it through the water panel, and releases it back into the living space as humidified air. The water panel is replaceable and designed for annual maintenance, promoting long-term functionality and hygiene.

The Aprilaire 400 also incorporates a simple installation process. With compatibility for various heating systems, including forced air and hydronic, it can be integrated into most homes without significant modifications. Its compact design is another advantage, ensuring it can fit unobtrusively in your home, maintaining the aesthetic of your space.

Overall, the Aprilaire 400 whole-home humidifier is a reliable solution for maintaining optimal humidity levels, fostering a healthier living environment, and enhancing overall comfort. With its advanced features, ease of use, and efficient operation, this humidifier is a smart investment for any homeowner aiming to improve indoor air quality and promote well-being.
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