The Ultimate Homeowner’s Guide to Aprilaire Humidifiers
October 2nd, 2025
27 min read
By Alex Largent

The Foundation of Home Comfort: Understanding Whole-Home Humidifiers
Proper humidity is a cornerstone of a comfortable and healthy home, yet it is often overlooked. During the heating season, furnaces produce dry air that can lead to discomfort, damage to the home, and even health issues. A whole-home humidifier integrates with a home’s HVAC system to add a controlled amount of moisture to the air, distributing it evenly through the ductwork to create a more balanced indoor environment.
How Does an Aprilaire Humidifier Work? A Clear, No-Nonsense Explanation
At its core, an Aprilaire whole-home humidifier operates on the principle of evaporation, a natural and efficient process for adding moisture to the air. The system is designed to work in conjunction with the furnace blower motor.
The process begins when the humidistat—the control unit for the system—detects that the relative humidity in the home has dropped below the desired setpoint. This sends a signal that initiates the humidification cycle. A 24-volt solenoid valve, acting as an automated gatekeeper, opens and allows water from the home’s plumbing to flow into the humidifier.
This water is directed onto a distribution tray at the top of the unit, which evenly wets a component called a water panel evaporator. This water panel, often made of a coated aluminum mesh, is the heart of the operation; its porous surface is designed for maximum water absorption and air exposure. As the furnace blower circulates warm air through the HVAC system, a portion of that air is directed through the moisture-laden water panel. The warm air causes the water on the panel to evaporate, turning it into water vapor. This humidified air is then distributed evenly throughout the entire house via the duct system, raising the relative humidity to a more comfortable level.
The Three Core Technologies: Bypass vs. Fan-Powered vs. Steam
Aprilaire offers three primary types of whole-home humidifiers. The correct choice for a home depends on several factors, including the type of HVAC system, the size and construction of the home, the regional climate, and the homeowner’s budget. Understanding the differences between these technologies is the first step in making an informed decision.
Bypass Humidifiers (e.g., Models 400, 500, 600)
Bypass humidifiers are the most common and budget-conscious option. These are passive systems that rely on the furnace’s blower motor and the pressure differential between the supply (warm air) and return (cool air) plenums of the ductwork. A 6-inch bypass duct is installed to connect these two plenums, creating a path for air to “bypass” the furnace and flow through the humidifier. The movement of air from the higher-pressure supply side to the lower-pressure return side naturally pushes air through the water panel, where it picks up moisture.
- Pros: These units are highly energy-efficient as they do not have their own fan motor, relying instead on the furnace’s blower. This also makes them very quiet during operation.
- Cons: Their performance is directly tied to the furnace’s runtime. In homes with high-efficiency, multi-stage furnaces that have shorter heating cycles, a bypass unit may struggle to produce enough humidity. They also require adequate space for the bypass duct, which can be a limitation in some installations.
Fan-Powered Humidifiers (e.g., Model 700)
Fan-powered humidifiers, also known as power humidifiers, are a step up in performance. These units contain a small, built-in fan that actively draws heated air from the furnace, pushes it through the water panel, and forces the now-humidified air back into the ductwork. This active process makes them more effective than bypass models and eliminates the need for a separate bypass duct, simplifying installation in tighter spaces.
- Pros: They can produce more humidity than bypass units and are capable of humidifying larger homes. Because they have their own fan, they can be wired to run independently of a heating cycle (a feature called “blower activation”), allowing for humidification whenever it’s needed, as long as the furnace blower is running.
- Cons: These units require a nearby 120V electrical outlet to power the fan. They have a slightly higher initial purchase and installation cost compared to bypass models.
Steam Humidifiers (e.g., Model 800)
Steam humidifiers represent the premium tier of whole-home humidification. Unlike evaporative models that rely on warm furnace air, a steam unit creates its own heat. It uses electrode technology, passing an electrical current through water held in a disposable canister. This current boils the water, producing pure, sterile steam that is then injected into the ductwork through a dispersion tube. This process is entirely independent of the heating cycle.
- Pros: Steam models offer the highest moisture output and the most precise humidity control. They are the best solution for very large homes (over 4,000 sq. ft.), homes in extremely dry or arid climates, or homes with valuable wood furniture, instruments, or flooring that require tight humidity control. Maintenance is also the simplest: the canister is replaced once per heating season, with no need for cleaning mineral buildup.
- Cons: They have the highest upfront cost for both the unit and installation, as they require a dedicated electrical circuit. There is also a recurring annual cost for the replacement canister.
Feature | Bypass Humidifier (Models 400, 500, 600) | Fan-Powered Humidifier (Model 700) | Steam Humidifier (Model 800) |
How It Works | Uses furnace blower pressure to pass air through a water panel via a bypass duct. | Uses a built-in fan to pull air through a water panel. | Boils water with electrodes to create steam and injects it into ductwork. |
Best For | Budget-conscious homeowners; homes with single-stage furnaces and adequate space. | Larger homes; homes with multi-stage or variable-speed furnaces; installations with limited space. | Very large homes; arid climates; homes with heat pumps or sensitive wood furnishings; precise humidity needs. |
Pros | Lowest cost, energy-efficient, quiet operation. | Higher output, can run with fan only, no bypass duct needed. | Highest capacity, fastest humidification, precise control, simple maintenance. |
Cons | Dependent on furnace runtime; may not be sufficient for all homes. | Requires 120V power; slightly higher cost and noise level than bypass models. | Highest initial and operating cost; requires dedicated electrical circuit and annual canister replacement. |
Estimated Installed Cost | $720 – $1,440 | $840 – $1,560 | $1,800 – $4,200 |
Annual Maintenance | Replace water panel once per season; clean distribution tray and drain line. | Replace water panel once per season; clean distribution tray and drain line. | Replace disposable steam canister once per season. |
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The Real Benefits of Balanced Humidity: Health, Home Preservation, and Energy Savings
Controlling your home’s humidity is not just about comfort; it provides tangible benefits for your health, your home’s structure, and even your wallet.
- Health and Wellness: Medical research has shown that maintaining an indoor relative humidity between 40-60% can significantly reduce the survival and transmission of airborne viruses, including influenza. Dry air can lead to dry nasal passages, scratchy throats, and irritated sinuses, making individuals more susceptible to respiratory infections. For those with allergies or asthma, balanced humidity helps minimize airborne dust mites, fungi, and other triggers that thrive in overly dry or damp conditions.
- Home Preservation: The air in a dry home acts like a sponge, pulling moisture from any available source. This includes hardwood floors, wood furniture, cabinetry, and musical instruments. Over time, this loss of moisture can cause wood to shrink, crack, and warp, leading to permanent damage. A whole-home humidifier protects these valuable investments by maintaining a stable level of moisture in the air.
- Energy Savings and Comfort: Humid air feels warmer than dry air at the same temperature. When the air has proper moisture content, the body’s natural cooling mechanism (evaporation from the skin) slows down, making the environment feel more comfortable. This allows many homeowners to lower their thermostat by a few degrees in the winter without sacrificing comfort, which can lead to noticeable savings on heating bills. Additionally, proper humidity reduces static electricity, eliminating those annoying shocks from carpets and doorknobs.
Selecting the Right Aprilaire Humidifier for Your Home
Choosing the correct humidifier involves more than just picking a model from a box. It requires an honest assessment of a home’s specific needs. An undersized unit will struggle to keep up, leading to disappointment, while an oversized unit may be an unnecessary expense.
A Practical Sizing Guide: Which Aprilaire Humidifier Do I Need?
The two most important factors in sizing a humidifier are the home’s total square footage and its construction “tightness,” which refers to how well it is sealed against outside air infiltration.
A common point of confusion for homeowners stems from the manufacturer’s specifications, which often list the maximum coverage area based on a “tightly constructed” home. However, most homes fall into the “average” or even “loose” categories, which significantly reduces the effective coverage of a given model. It is critical to size the unit based on a realistic assessment of the home’s condition.
- Tight Construction: Typically newer homes built with modern standards, featuring house wrap, high-quality sealed windows, and a focus on minimizing air leaks.
- Average Construction: Most homes fall into this category. They have decent insulation and some weatherstripping but may have minor drafts around windows and doors.
- Loose Construction: Often older homes with little to no insulation in the walls, original single-pane windows, and noticeable drafts.
Based on these factors, here are some practical recommendations:
- Aprilaire 500 (12 Gallons Per Day): Best suited for smaller, tightly built homes up to 3,600 sq. ft. For an average home, its effective range is closer to 1,500 sq. ft..
- Aprilaire 600 (17 Gallons Per Day): An excellent all-around choice for many homes. It can cover up to 5,000 sq. ft. in a tight home, but is more realistically sized for an average home of about 2,000-2,500 sq. ft..
- Aprilaire 700 (18 Gallons Per Day): The fan-powered design gives it a slight edge in output. It is rated for up to 5,300 sq. ft. in a tight home and is a strong choice for average homes up to 3,000 sq. ft..
- Aprilaire 800 (Up to 34.6 Gallons Per Day): The steam unit is the definitive choice for any home over 4,000 sq. ft., regardless of construction, or for smaller homes located in very arid climates where evaporative models struggle to keep up.
An Honest Comparison: Aprilaire vs. Honeywell Humidifiers
When shopping for a whole-home humidifier, the two brand names that appear most often are Aprilaire and Honeywell. Both are reputable manufacturers that produce reliable products, and from the outside, many of their bypass and fan-powered models appear very similar. However, there are some differences to consider.
Aprilaire holds a significant place in the industry, having introduced the first whole-home humidifier in 1954, and it remains the most popular brand among HVAC professionals. Their systems are known for their robust construction and straightforward design.
Honeywell units also have a strong reputation and incorporate slightly different technologies. For example, some Honeywell models feature a “PerfectFlo” water distribution tray and use AgION anti-microbial coating on their water pads to inhibit mold and bacteria growth.
There can also be differences in control systems and warranties. Some comparisons suggest Honeywell’s controls may offer more consistent performance, while warranty terms can vary between models and distributors for both brands. It is always best for homeowners to confirm the specific warranty details with their installing contractor.
From a professional’s perspective, the performance difference between comparable Aprilaire and Honeywell evaporative models is often minimal. The success of the installation depends more on choosing the right type of technology (bypass, fan, or steam) for the home and ensuring the unit is sized and installed correctly by an experienced technician.
The Complete Aprilaire Humidifier Model Encyclopedia
This section provides a detailed breakdown of the main Aprilaire humidifier models currently available. Each model is designed to meet different needs, and understanding their specifications is key to selecting the right one.
Model | Type | Capacity (GPD) | Coverage (Sq. Ft. – Tight) | Key Feature | Estimated Installed Cost |
800 | Steam | 11.5 – 34.6 | Up to 6,200 | Highest output and precision, independent of furnace heat. | $1,800 – $4,200 |
700 | Fan-Powered | 18 | Up to 5,300 | High output, no bypass duct required. | $840 – $1,560 |
600 | Bypass | 17 | Up to 5,000 | The most popular model, great balance of performance and value. | $720 – $1,080 |
500 | Bypass | 12 | Up to 3,600 | Compact design for small to mid-sized homes. | $660 – $960 |
400 | Bypass | 17 | Up to 5,000 | Water-saving design with 100% water efficiency. | $780 – $1,140 |
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The Aprilaire 800 Series (Steam): The Powerhouse Solution
The Aprilaire 800 is the premier solution for whole-home humidification. It operates independently of the furnace temperature, delivering a precise amount of pure steam humidity on demand. This makes it the most effective option for any home, especially those in arid climates or with large open floor plans, extensive woodwork, or hydronic heating systems.
- Specifications:
- Type: Steam, using electrode technology.
- Capacity: The output is adjustable and depends on the electrical voltage. It can produce from 11.5 GPD on a 120V circuit up to 34.6 GPD on a 240V, 16.0 Amp circuit.
- Coverage: Effectively humidifies tightly built homes up to 6,200 sq. ft..
- Dimensions: Approximately 20.9 inches H x 10.1 inches D x 7.1 inches W.
- What’s in the Box: The unit comes with the Model 62 Automatic Digital Humidifier Control, one Model 80 Steam Canister, an outdoor temperature sensor, steam hose, and a dispersion tube for duct installation.
- Common Parts:
- Model 80 Steam Canister: This is the core component that boils the water. It is a consumable part that must be replaced annually.
- Solenoid Valve (Fill Valve): This valve controls water flow into the canister. While reliable, it can fail over time.
- Estimated Installed Cost:
- The Aprilaire 800 requires a dedicated electrical circuit, which adds to the installation complexity and cost. For a free exact quote on a new installation, please contact us. As a general guideline, a professional installation of an Aprilaire 800 typically ranges from $1,800 to $4,200. Please note that pricing varies, as different dealers pay different prices for equipment in various parts of the country.
The Aprilaire 700 Series (Fan-Powered): High-Output Performance
The Aprilaire 700 is a high-capacity fan-powered model that provides excellent performance for larger homes without the higher cost of a steam unit. Its internal fan makes it more effective than bypass models, especially on systems with variable-speed blowers or shorter run times.
- Specifications:
- Type: Fan-Powered Evaporative.
- Capacity: Produces up to 18 gallons per day (GPD), with an evaporation rate of 0.75 gallons per hour.
- Coverage: Suitable for tightly constructed homes up to 5,300 sq. ft. For average homes, it is a solid choice for spaces up to 3,000 sq. ft..
- Dimensions: Approximately 18 inches H x 15.9 inches W x 10.3 inches D.
- What’s in the Box: The package includes the Model 700 humidifier, the Model 60 Automatic Digital Control, one Model 35 Water Panel, an outdoor temperature sensor, and a 24VAC transformer.
- Common Parts:
- Model 35 Water Panel: This is the standard replacement panel for the 700 series and should be replaced once or twice per heating season.
- Solenoid Valve (Part #4040): The same reliable valve used in other evaporative models.
- Estimated Installed Cost:
- For a free exact quote on a new installation, please contact us. As a general guideline, a professional installation of an Aprilaire 700 typically ranges from $840 to $1,320. Please note that pricing varies, as different dealers pay different prices for equipment in various parts of the country.
The Aprilaire 600 Series (Bypass): The All-Around Workhorse
The Aprilaire 600 is arguably the most popular whole-home humidifier on the market. As a large bypass unit, it offers an excellent combination of capacity, reliability, and value, making it the go-to choice for many average-to-large sized homes with standard forced-air furnaces.
- Specifications:
- Type: Bypass Evaporative.
- Capacity: Produces up to 17 GPD, with an evaporation rate of 0.70 gallons per hour.
- Coverage: Rated for tightly built homes up to 5,000 sq. ft..
- Dimensions: Approximately 15.75 inches H x 15.4 inches W x 10.25 inches D.
- What’s in the Box: Includes the Model 600 humidifier with built-in damper, the Model 60 Automatic Digital Control, one Model 35 Water Panel, an outdoor temperature sensor, and a 24VAC transformer.
- Common Parts:
- Model 35 Water Panel: The standard replacement panel.
- Solenoid Valve (Part #4040): A common replacement part for evaporative models.
- Estimated Installed Cost:
- For a free exact quote on a new installation, please contact us. As a general guideline, a professional installation of an Aprilaire 600 typically ranges from $720 to $1,080. Please note that pricing varies, as different dealers pay different prices for equipment in various parts of the country.
The Aprilaire 500 Series (Bypass): The Compact Solution
The Aprilaire 500 is a compact bypass humidifier designed to bring the benefits of whole-home humidification to smaller or mid-sized homes where the larger capacity of the 600 series is not needed. It offers the same reliable technology in a smaller footprint.
- Specifications:
- Type: Bypass Evaporative.
- Capacity: Produces up to 12 GPD, with an evaporation rate of 0.5 gallons per hour.
- Coverage: Rated for tightly built homes up to 3,600 sq. ft..
- Dimensions: Approximately 13 inches H x 15.6 inches W x 10.25 inches D.
- What’s in the Box: Includes the Model 500 humidifier with built-in damper, the Model 60 Automatic Digital Control, one Model 10 Water Panel, an outdoor temperature sensor, and a 24VAC transformer.
- Common Parts:
- Model 10 Water Panel: The replacement panel for the 500 series.
- Solenoid Valve (Part #4040): A common replacement part for evaporative models.
- Estimated Installed Cost:
- For a free exact quote on a new installation, please contact us. As a general guideline, a professional installation of an Aprilaire 500 typically ranges from $660 to $960. Please note that pricing varies, as different dealers pay different prices for equipment in various parts of the country.
The Aprilaire 400 Series (Water-Saving Bypass): The Efficiency-Focused Choice
The Aprilaire 400 is a unique bypass humidifier designed for homeowners who are particularly conscious of water conservation. Unlike standard flow-through models that continuously drain excess water, the Model 400 uses a reservoir to wick 100% of the supplied water for evaporation, eliminating the need for a floor drain.
- Specifications:
- Type: Water-Saving Bypass Evaporative.
- Capacity: Produces up to 17 GPD, matching the output of the Model 600.
- Coverage: Rated for tightly built homes up to 5,000 sq. ft..
- Dimensions: Approximately 15.75 inches H x 15.4 inches W x 10.25 inches D.
- What’s in the Box: Includes the Model 400 humidifier, the Model 60 Automatic Digital Control, two Model 45 Water Panels, an outdoor temperature sensor, and a 24VAC transformer.
- Common Parts:
- Model 45 Water Panel: Due to its water-saving design, this panel requires more frequent replacement, typically twice per heating season.
- Solenoid Valve (Part #4040): A common replacement part for evaporative models.
- Estimated Installed Cost:
- For a free exact quote on a new installation, please contact us. As a general guideline, a professional installation of an Aprilaire 400 typically ranges from $780 to $1,140. Please note that pricing varies, as different dealers pay different prices for equipment in various parts of the country.
A Guide to Older & Other Models (110, 224, 350, 360, 550, 560, 760)
Many homes are still equipped with older, discontinued Aprilaire models. While these units are no longer in production, replacement parts, particularly water panels, are readily available.
- Model 110/112: These were older fan-powered models. They have been succeeded by the Model 700 series. The Model 110 uses the #10 Water Panel, and the Model 112 uses the #12 Water Panel.
- Model 220/224: These were older bypass models. The Model 220 uses the #10 Water Panel, and the Model 224 uses the #12 Water Panel. They are functionally replaced by the 500 and 600 series.
- Model 350/360: These are self-contained evaporative humidifiers designed for homes without forced-air ductwork, such as those with boilers or radiant heat. They use a built-in fan and require ducting to a central location. Both use the #35 Water Panel.
- Model 550: An older bypass model that used the #10 Water Panel. It has been replaced by the modern Model 500.
- Model 560: A popular older bypass model that has been succeeded by the Model 600 series. It uses the #35 Water Panel.
- Model 760: An older fan-powered model that has been replaced by the modern Model 700 series. It uses the #35 Water Panel.
Decoding Model Numbers: Automatic vs. Manual (e.g., 600 vs. 600M)
A common point of confusion when selecting a humidifier is the letter at the end of the model number. The primary difference between models ending in “M” (like the 600M or 700M) and those with no letter or an “A” (like the 600 or 700A) is the type of control unit included with the humidifier.
- “M” for Manual: Models with an “M” suffix come packaged with a manual humidistat. This type of control requires the homeowner to adjust the humidity setting dial based on changes in the outdoor temperature to prevent condensation on windows.
- “A” or No Letter for Automatic: Models without a letter suffix (like the 500, 600, 700) or with an “A” (like the older 700A) include an automatic digital control. These controls come with an outdoor temperature sensor that allows the system to adjust the indoor humidity level automatically, offering a “set it and forget it” convenience.
Many modern Aprilaire units, like the current Model 600, now ship with a digital control that can be operated in either manual or automatic mode, simplifying the product line. Homeowners who plan to use a smart thermostat (like a Nest or Ecobee) to manage their humidifier often choose an “M” model, as the smart thermostat takes over the control functions, making the more advanced automatic humidistat redundant.
Consumer Feedback and Long-Term Reliability
Homeowner reviews for Aprilaire humidifiers are generally positive but highlight some common concerns regarding long-term reliability. Many users report a noticeable improvement in home comfort, praising the effectiveness of the units, particularly the “set it and forget it” functionality of the automatic models. The Model 800 steam humidifier is often cited for its powerful performance, with users wishing they had installed one sooner.
However, there are recurring complaints. For the high-end Model 800, the significant installation cost—sometimes reported as high as $3,500—and the annual expense of replacing the steam canister are notable drawbacks. Several owners have reported premature failure of key components like drain valves, control boards, and solenoids, often occurring just outside the five-year warranty period and leading to costly repairs. Leaking is another frequently mentioned issue, especially with the popular Model 600, where water can miss the drain and leak onto the furnace or floor. Some users of bypass models also express frustration that their units struggle to consistently reach the desired humidity levels.
Overall, while many homeowners are satisfied with the immediate performance of their Aprilaire humidifiers, there is a pattern of feedback suggesting that long-term reliability and the cost of parts and service can be a concern.
Installation, Setup, and Seasonal Operation
Proper installation and operation are critical for getting the most out of a whole-home humidifier. While installation is best left to a professional, understanding how the system works and how to manage it seasonally empowers homeowners to maintain optimal comfort and efficiency.
Aprilaire Humidifier Installation: A Professional’s Perspective
Installing a whole-home humidifier involves sheet metal cutting, plumbing, and low-voltage electrical work. For safety, proper function, and to ensure the manufacturer’s warranty remains valid, installation should be performed by a qualified HVAC contractor.
The general process for an evaporative model involves these key stages:
- Safety First: The first and most important step is to completely disconnect electrical power to the furnace at the circuit breaker.
- Location and Cutting: The installer will use a template to mark and cut an opening in the supply or return air plenum. Care must be taken to avoid damaging the air conditioning coil.
- Mounting: The humidifier’s base is then securely fastened to the plenum with sheet metal screws.
- Bypass Ducting (for Bypass Models): For models like the 600 or 500, a 6-inch collar is installed on the opposite plenum, and a section of ductwork is run to connect it to the humidifier’s bypass opening.
- Plumbing: A saddle valve is used to tap into a nearby water pipe. For best performance, connecting to a hot water line is recommended, as the heat aids evaporation. A 1/4-inch copper or plastic tube is run from the valve to the humidifier’s solenoid valve. A separate 1/2-inch drain hose is run from the bottom of the humidifier to a nearby floor drain.
- Wiring: The humidistat, solenoid valve, and transformer are wired into a 24-volt circuit. This circuit is configured to activate the humidifier only when the furnace blower is running.
- Commissioning: Once all connections are made, the technician will turn the water and power back on, set the humidistat to test mode, and verify that water is flowing correctly and there are no leaks.
Seasonal Startup and Shutdown: How to Turn Your Humidifier On and Off
Properly preparing the humidifier for each season is a simple but essential task. Forgetting these steps is a common reason homeowners believe their unit is not working.
Turning On for the Winter Heating Season
- Open the Damper (Bypass Models Only): Locate the damper handle on the bypass duct connected to the humidifier. Turn it to the “WINTER” or “OPEN” position. This allows air to flow through the humidifier.
- Turn on the Water Supply: Find the small saddle valve on the water pipe that supplies the humidifier. Turn the handle counter-clockwise until it is fully open.
- Set the Humidistat: Turn the control dial on the humidistat from the “OFF” position to a desired setting for winter, typically around 35% to start.
Turning Off for the Summer Cooling Season
- Turn Off the Humidistat: Turn the control dial to the “OFF” position. This will prevent the humidifier from activating.
- Close the Damper (Bypass Models Only): Turn the damper handle to the “SUMMER” or “CLOSED” position. This is a critical step, as it prevents cool, dehumidified air from your air conditioner from being needlessly cycled through the humidifier, which would reduce A/C efficiency.
- Turn Off the Water Supply: Close the saddle valve. This prevents water from sitting stagnant in the unit’s reservoir and lines throughout the summer.
Setting Your Aprilaire Humidifier for Winter and Summer
The ideal humidity setting for winter is a moving target that changes with the outdoor temperature. Setting it too high on a very cold day will lead to condensation on windows and other cold surfaces.
Winter Settings
For optimal comfort without causing condensation, the recommended indoor relative humidity (RH) level decreases as the outdoor temperature drops. The following chart is a reliable guide for manual adjustments :
If Outdoor Temperature is… | Set Indoor Humidity to… |
+20°F (-7°C) and above | 35% RH |
+10°F (-12°C) | 30% RH |
0°F (-18°C) | 25% RH |
-10°F (-23°C) | 20% RH |
-20°F (-29°C) | 15% RH |
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Homeowners with an automatic digital control and a functioning outdoor temperature sensor do not need to make these adjustments manually. They can simply set the dial to a number (e.g., “5” is a good starting point) and the system will automatically adjust the indoor RH target based on the outdoor temperature.
Summer Settings
During the summer, the humidifier should be turned completely off at the humidistat. The air conditioner is working to remove humidity from the air, so running the humidifier at the same time would be counterproductive, waste energy, and create an uncomfortable, muggy environment in the home.
Mastering Your Controls: Manual vs. Automatic Digital Humidistats
Aprilaire humidifiers are controlled by a humidistat, which functions like a thermostat but for humidity. There are two main types.
- Manual Humidistat (e.g., Model 4655): This is a simple control with a dial marked with humidity percentages. The homeowner is responsible for adjusting this dial up or down according to the outdoor temperature, following the chart provided above. While effective, it requires regular attention during periods of fluctuating weather.
- Automatic Digital Humidistat (e.g., Model 60/62): This is the modern standard included with most new Aprilaire humidifiers. It is wired to a small sensor mounted outside the home. This allows the control to read the outdoor temperature and automatically calculate the maximum safe indoor humidity level to prevent condensation. The homeowner simply sets a dial (typically numbered 1 through 7) to their general preference—”5″ is a normal starting point—and the system handles the rest. This “set it and forget it” functionality provides more consistent comfort and protection for the home. These controls often include a “Blower Activation” switch, which, when turned on, gives the humidistat permission to run the furnace fan to add humidity even when there isn’t a call for heat. This feature is particularly useful for maximizing humidity output but requires the humidifier to be connected to a hot water supply.
A Deeper Look at Wiring: From Furnace Boards to Smart Thermostats
Disclaimer: The following information is for educational purposes only. All electrical work should be performed by a qualified and licensed HVAC professional to ensure safety and proper operation.
The basic control circuit for an Aprilaire evaporative humidifier is a simple 24-volt series circuit. Power flows from a source, through the humidistat, and to the solenoid valve. When the humidistat calls for humidity, it closes the circuit, which energizes the solenoid and allows water to flow.
There are a few common ways to power this circuit:
- Dedicated 24V Transformer: Most Aprilaire humidifiers come with a dedicated transformer. This device is wired to a 120V power source and safely steps the voltage down to the 24V needed for the control circuit. This is the most reliable and recommended method of installation.
- Furnace Control Board Terminals: Many modern furnaces have accessory terminals on their main control board, often labeled “HUM” (for a 24V hot) and “C” (for common). These terminals are typically energized only when the furnace is in a heating cycle, providing a convenient and safe way to power the humidifier so that it only runs when there is heat. A common professional practice is to wire the humidifier control to the “W” (heat) and “C” (common) terminals, which achieves the same result.
- Model 50 Current Sensing Relay: For older furnaces that lack dedicated accessory terminals, a Model 50 Current Sensing Relay can be used. This small device clamps around the main power wire for the furnace’s blower motor. When it detects current flowing through the wire (meaning the fan is on), it closes an internal switch, completing the humidifier’s control circuit. This ensures the humidifier can only operate when air is circulating.
Smart Thermostat Integration (Nest, Ecobee)
Smart thermostats like Nest and Ecobee can control an Aprilaire humidifier directly, often eliminating the need for the Aprilaire-provided humidistat. This integration typically requires one or two dedicated wires running from the thermostat to the humidifier.
- 1-Wire Setup (Bypass/Evaporative Models): For a standard bypass humidifier, a single wire is run from the thermostat’s accessory terminal (often labeled “*” or “ACC+”) to one of the two wires on the humidifier’s solenoid valve. The other solenoid wire is connected directly to the 24V “C” (common) terminal on the furnace control board. The thermostat then uses the furnace’s 24V power to open and close the solenoid valve when humidity is needed.
- 2-Wire Setup (Powered or Steam Models): Fan-powered and steam humidifiers often have their own internal power and cannot have the furnace’s 24V power sent directly to them. In these cases, the smart thermostat acts as a dry-contact switch. This requires two wires from the thermostat’s accessory terminals (e.g., ACC+ and ACC-) connected to the humidifier’s control input. Alternatively, a single acce
The Essential Maintenance and Troubleshooting Guide
Proper maintenance is the key to ensuring an Aprilaire humidifier operates efficiently and reliably for many years. Most issues homeowners encounter are related to a lack of basic maintenance or simple operational errors.
Step-by-Step: How to Change an Aprilaire Humidifier Water Panel
Replacing the water panel is the single most important maintenance task. It should be done at least once a year, typically at the start of the heating season. In areas with very hard water, it may need to be done twice.
- Prepare the Unit: Turn the humidistat to the “OFF” position and shut off the water supply by closing the saddle valve.
- Remove the Cover: Unlatch the front cover of the humidifier. It should pull off easily.
- Remove the Water Panel Assembly: The water panel is housed inside a black or grey plastic frame. Grasp this frame at the top and pull it straight out of the humidifier base.
- Disassemble the Frame: The water distribution tray is snapped onto the top of the frame. Gently unsnap it to separate it from the main frame.
- Swap the Panel: Slide the old, crusty water panel out of the frame. Insert the new panel. This is a critical step: The new water panel will have a colored paint mark (often red or black) on one edge. This mark must be facing UP when the panel is installed. This ensures proper water distribution.
- Reassemble and Reinstall: Snap the distribution tray back onto the top of the frame. Slide the entire assembly back into the humidifier, ensuring the bottom of the frame is properly seated over the drain spud.
- Final Steps: Re-attach the front cover, turn the water supply back on, and turn the humidistat back to your desired winter setting. If the control has a “Change Water Panel” indicator light, turn the dial to the “Test/Reset” position for a few seconds to reset the maintenance timer.
Step-by-Step: How to Clean Your Aprilaire Humidifier
Annual cleaning should be performed at the same time the water panel is replaced.
- Water Distribution Tray: After removing it from the frame, inspect the small V-shaped notches for mineral buildup. Use a small brush or paperclip to gently clean them out. Do not aggressively scrub the textured coating on the bottom of the tray, as this helps distribute water evenly.
- Frame/Scale Control Insert: The main frame that holds the panel can accumulate significant mineral deposits. Flex the plastic or use a putty knife to gently scrape off the buildup.
- Drain Line: Disconnect the 1/2-inch drain hose from the bottom of the humidifier. Take it to a sink and flush it with high-pressure water to clear any sediment or blockages that could cause a leak.
- Humidifier Base: Wipe out any sediment or mineral deposits from the bottom of the humidifier housing.
Troubleshooting Common Problems
Most humidifier issues can be traced to a few common causes. Before calling for service, running through this checklist can often solve the problem.
My Humidifier Isn’t Working or Turning On
- Check the Season Settings: Is it the heating season? Ensure the bypass damper is set to “WINTER,” the water supply is on, and the humidistat is turned ON and set to a level higher than the current humidity.
- Check the Furnace: Most evaporative models will only run when the furnace is running and calling for heat. Make sure the thermostat is set to “HEAT” and the temperature is set high enough to start a heating cycle.
- Check for Power: Listen for a “click” from the solenoid valve when the furnace and humidifier should be running. If there is no click, the issue is likely electrical. A professional can test for 24V power at the solenoid. If power is present but the valve doesn’t click, the solenoid has failed. If there is no power, the problem is further up the line in the humidistat, wiring, or furnace connections.
My Humidifier Is Leaking Water
- Clogged Drain Line: This is the most common cause of leaks. A buildup of minerals in the drain hose can cause water to back up and overflow from the humidifier housing. Disconnect and flush the drain line to clear it.
- Improperly Seated Water Panel: If the water panel assembly is not correctly seated in the drain spud at the bottom of the unit, water can miss the drain and leak out.
- Stuck Solenoid Valve: If the solenoid valve is stuck in the open position, water will flow continuously, even when the humidifier is off, eventually causing an overflow. If water is always running to the drain, the solenoid needs to be replaced.
- Cracked Housing: In rare cases, the plastic housing or distribution tray can develop a crack. A visual inspection can confirm this.
My Humidifier Isn’t Getting Water (Solenoid Valve Issues)
The solenoid valve is the most frequently replaced part on an evaporative humidifier. Its job is to open and close thousands of times per season, and it is highly susceptible to failure from mineral buildup in hard water.
- Symptoms: The furnace is running, the humidistat is calling for humidity, and the humidifier fan may be on, but no water is flowing through the unit and no water is going down the drain.
- The Ultimate Solenoid Valve Troubleshooting Guide:
- Listen for the “Click”: When the humidifier is supposed to be running, listen closely to the solenoid valve (the small brass component where the water line connects). A distinct “click” indicates the valve’s internal coil is receiving power and trying to open.
- If There Is NO Click: The problem is electrical. A technician would use a multimeter to confirm there is no 24V power at the two wires connected to the solenoid. The issue lies with the humidistat, wiring, or power source.
- If There IS a Click, But No Water Flow: This isolates the problem to a water blockage or a mechanical failure inside the valve.
- Test the Water Supply: Turn off the water supply at the saddle valve. Place a small bowl under the solenoid and carefully loosen the compression nut on the inlet side (where the water line comes from the pipe). Slowly open the saddle valve for a second. If water drips out, the water supply is good. If not, the saddle valve is either closed or clogged and needs to be serviced or replaced.
- Test the Solenoid Itself: If the water supply is confirmed, tighten the inlet nut and loosen the outlet nut (where the tube goes into the humidifier). Turn the water back on and activate the humidifier. If the solenoid clicks but only a dribble of water comes out, the valve is internally clogged or has failed. It must be replaced.
Decoding Control Panel Lights and Error Codes (R1, R3, E3)
The lights and codes on Aprilaire controls can sometimes be confusing.
- “Change Water Panel” Light: This light on the Model 60/62 digital control is simply a timer. It activates after a pre-set number of runtime hours to remind the homeowner to perform annual maintenance. It does not actually sense if the panel is dirty. After changing the panel, this timer must be reset by turning the control dial to the “Test/Reset” position for a few seconds.
- Aprilaire 800 Steam Humidifier Indicator Lights: The Model 800 has a series of diagnostic lights. A solid green “On” light is normal. A solid red “Fill” light indicates a fill fault. A solid yellow “Steam” light means the unit has been running a long time but hasn’t reached full capacity (often due to low water conductivity). A flashing or solid red “Service” light indicates an overcurrent fault, which usually means the canister is at the end of its life and needs to be replaced.
- Error Codes R1, R3, E3: Homeowners sometimes report seeing “R1” or “R3” on their digital control during a test cycle. These are not error codes. They are simply software revision numbers for the control board’s firmware and do not indicate a problem. The “E3” error code is primarily seen on Aprilaire dehumidifiers and indicates a communication failure with a remote control, usually due to a loose wire.
Frequently Asked Technical Questions
- What size is the drain hose? The standard drain hose for most Aprilaire evaporative humidifiers has a 1/2-inch inner diameter (I.D.).
- Should I use hot or cold water for my humidifier? Aprilaire humidifiers can operate with cold, hot, hard, or softened water. However, using a hot water supply (up to a maximum of 140°F) is highly recommended as it improves the evaporation rate and overall performance. This is especially beneficial for fan-powered models and when using the “Blower Activation” feature, as the unit may be running without supplemental heat from the furnace.
- What is “Blower Activation” and when should I use it? Blower Activation is a feature available on Aprilaire’s automatic digital controls. When the “Blower Activation” switch is set to “ON,” it gives the humidistat permission to turn on the furnace fan by itself, even if there is no call for heat from the thermostat. If the control detects that the home’s humidity has dropped below the setpoint, it will run the fan to circulate air through the humidifier and add moisture to the home. This is a great way to maximize humidity output, but it is recommended to have the humidifier connected to a hot water supply when using this feature for best results.
A Clear Look at Parts, Service, and Costs
Understanding the costs associated with parts, repairs, and new installations is essential for making informed decisions about a home’s humidity control system.
The Complete Guide to Aprilaire Humidifier Parts
Many common maintenance and repair tasks involve replacing specific components. The following table lists common replacement parts. Homeowners can often find these parts online or through an HVAC supplier.
Part Name | Common Part Number | Function & Compatible Models |
Water Panel | #35 | Evaporative media for Models 350, 360, 560, 600, 700, 760. |
Water Panel | #10 | Evaporative media for Models 110, 220, 500, 550. |
Water Panel | #45 | Evaporative media for Model 400 (requires two per season). |
Solenoid Valve | #4040 | Controls water flow for all evaporative models except very old ones. |
Steam Canister | #80 | Boils water in Model 800/865 steam humidifiers. |
Current Sensing Relay | #50 | Activates humidifier with furnace blower on older systems. |
Manual Humidistat | #4655 | Manual humidity control dial. |
Digital Control | #60 / #62 | Automatic humidity control for evaporative/steam models. |
Export to Sheets
It is not uncommon for homeowners to see a part for sale online and then receive a quote from a professional contractor for the same part at a much higher price. This difference does not necessarily mean the contractor is overcharging. A professional service call includes not only the cost of the part itself, but also the technician’s travel time, their diagnostic expertise, the labor to perform the replacement correctly, and the company’s overhead and warranty on the completed work.
Aprilaire Humidifier Repair: When to Call a Pro and What to Expect
While tasks like changing a water panel are simple for most homeowners, any repair involving electrical wiring or plumbing connections should be handled by a qualified HVAC technician.
A professional service call typically begins with a diagnostic fee. This covers the cost of sending a trained technician to the home and the time required to accurately diagnose the problem. This fee is separate from the cost of parts and labor for the actual repair. Please note that different dealers charge different prices in different parts of the country. Based on the diagnostic findings, common repairs include replacing the solenoid valve, the humidistat, or the fan motor on fan-powered models.
Per our company policy, we do not provide free exact quotes for repair services. The prices listed above are for general informational purposes only.
A Detailed Breakdown of Aprilaire Humidifier Installation Costs
For homeowners considering a new whole-home humidifier, we offer a free, no-pressure exact quote for a full installation. The total cost can depend on the specific model chosen, the complexity of the installation, and local labor rates.
The following are typical installed price ranges, which include the cost of the unit and all necessary labor and materials.
- Bypass Models (400, 500, 600): Total installation cost typically ranges from $720 to $1,440.
- Fan-Powered Models (700): Total installation cost typically ranges from $840 to $1,560.
- Steam Models (800): Due to the need for a dedicated electrical circuit, installation is more involved. Total installation cost typically ranges from $1,800 to $4,200.
Please note that these are estimated price ranges. Prices can vary significantly, as different dealers pay different prices for equipment and labor rates change from one part of the country to another.
Understanding Your Aprilaire Warranty
Aprilaire humidifiers typically come with a five-year limited warranty on parts, which begins on the date of installation. A critical condition of this warranty is that the unit must be installed by a qualified heating and air conditioning contractor; failure to do so will void the warranty.
The warranty covers defects in materials or workmanship for the humidifier unit itself. However, it explicitly excludes several items :
- Consumable Parts: Routine maintenance items like water panels and steam canisters are not covered.
- Labor Costs: The warranty does not cover any labor charges associated with diagnosis, repair, removal, or reinstallation of parts.
- Improper Installation: Any damage or defects resulting from improper installation or failure to follow the provided instructions are not covered.
To make a warranty claim, a homeowner should contact the contractor who installed the unit.
Product Safety and Recall Information
There is an important safety recall for certain steam humidifiers manufactured by Research Products Corporation, including some Aprilaire models. The recall was issued because a specific type of electrode wire with a “D” shaped connector can loosen, potentially causing arcing or overheating at the canister connection, which poses a fire hazard.
- Affected Models: The recall includes Aprilaire Steam Humidifier models 800, 801, 865, and 866 that were produced between June 2010 and January 2015. Units sold under other brand names (Carrier, Bryant, York, etc.) are also affected.
- The Hazard: There have been over 100 reports of these units overheating, including 10 incidents that resulted in residential fires and significant property damage.
- Remedy: Homeowners with an affected unit should immediately stop using it and contact Research Products Corporation to receive a free electrode wire repair kit. This kit must be installed by a qualified contractor.
About the Brand and Our Commitment
Who Makes Aprilaire Humidifiers? A Brief History of an Industry Leader
Aprilaire is a brand owned by Research Products Corporation, a company founded in Madison, Wisconsin, in 1938. The company’s journey into indoor air quality was born from a local need: combating the intensely dry air of Wisconsin winters. In 1954, this focus led to a major innovation: the invention of the first truly effective whole-home evaporative humidifier.
This pioneering spirit established Aprilaire as a leader in the field. Over the following decades, the company expanded its expertise and product lines to address all aspects of indoor air quality, developing a full suite of solutions that includes air purifiers, dehumidifiers, fresh air ventilators, and advanced control systems. Aprilaire maintains its reputation for quality and innovation by working closely with key industry organizations like the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) to ensure its products meet the highest standards of performance and engineering.
The Honest Fix Promise: Our Commitment to Clear Answers and Quality Work
This guide was created in the spirit of the Honest Fix mission: to provide homeowners with the clear, straightforward information they need to make confident decisions about their home’s comfort and safety.[112, 112] As an HVAC educator with over two decades of experience, the goal is to empower homeowners with knowledge, not to pressure them with a sales pitch.
Whether a homeowner is looking to perform simple maintenance, troubleshoot a problem, or invest in a new system, having access to honest, technically accurate information is the first step. The principles of doing the right thing, communicating clearly, and standing behind every job are the foundation of trustworthy service.
For a free exact quote on a new Aprilaire humidifier installation, or to schedule service with a team that believes in doing things the thorough way, please contact us. No Upsells. No Games. Just Honest Fixes.
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