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Millions of Americans have been diagnosed with sleep apnea, a medical condition that causes temporary loss of breath during sleep and is also linked to heavy snoring. The most common forms of this disorder are obstructive sleep apnea (OSA) and central sleep apnea (CSA). While there is currently no cure for sleep apnea, positive air pressure, or PAP, therapy is commonly prescribed to treat the condition. This form of therapy requires an airflow generator (also known as a PAP machine) that draws in outside air using an electric fan, pressurizes and humidifies the air, then delivers it to the user through a connective hose and a nasal or full face mask. Types of PAP therapy include continuous positive air pressure (CPAP), bi-level positive air pressure (BiPAP), and automatic positive air pressure (APAP).
The PAP machine humidifier plays a crucial role during CPAP, BiPAP, or APAP therapy. By adding moisture to the pressurized air, users experience less irritation in their breathing passages and are at lower risk for other side effects of PAP therapy, such as congestion and frequent nosebleeds. Humidifiers may be heated or cold. Additionally, the humidifier may be integrated or built into the machine, or used as a standalone device. Prices for humidifiers vary by model and type, but most cost between $50 and $250.
This guide will explore common designs and functions of PAP humidifiers, compare different types of humidifiers sold today, and provide some buying and maintenance tips for first-time owners.
Designs and Characteristics of PAP Humidifiers
PAP machines deliver airflow at specific pressurized settings. The pressure of this airflow is measured in centimeters of water (cmH20); most machines offer a pressure range of 4 to 20 cmH20. CPAP machines provide a steady (or continuous) pressure rate throughout the night; BiPAP machines deliver two airflow rates, a higher rate for inhalation and a lower rate for exhalation; and APAP machines deliver a variable pressure rate based on the user’s breathing patterns.
Humidifiers ease the breathing process for sleepers receiving CPAP, BiPAP, or APAP therapy. The airflow from PAP machines can be an irritant, especially at higher pressure settings. Without humidified air, PAP recipients are susceptible to the following:
Irritation in the nasal and throat passages
Frequent bloody or runny noses
These issues are particularly commonplace during the early stages of PAP therapy, when sleepers are not yet accustomed to the process. If these problems persist, PAP users are at risk for infections as well.
The following sequence demonstrates how PAP machine humidifiers work:
The humidifier’s open chamber or chambers are filled with water.
Once the PAP machine is turned on, the electric fan sucks in outside air.
The air is channeled over the open water chamber(s), where it collects moisture.
The humidified air is then delivered to the user through the connective hose and face mask.
In terms of design, humidifiers generally fall into one of the following three categories.
Integrated: An integrated humidifier is detachable. It is designed for use with specific PAP machines, and will not be compatible with other models.
Built-in: A built-in humidifier cannot be removed, but the water chambers are detachable for filling and cleaning.
Standalone: A standalone humidifier is not attached to the PAP machine. It will be compatible with most PAP machines. Because they are separate devices, a second connective hose and power cord are needed to operate these humidifiers.
The table below illustrates the similarities and differences between the three humidifier types:
Average Price Range
Detachable Second hose and power cord not required
Remove humidifier to fill with water
Small and compact Travel-friendly Fewer parts required Wide availability
Incompatible with most machines Smaller size provides less humidification
$100 to $200
Non-detachable Second hose and power cord not required
Remove chambers to fill with water
Small and compact Fewer parts required
Smaller size provides less humidification Replacement machine needed for humidifier repairs
$400+ (includes machine)
Not attached to PAP machine Second hose and power cord required
Removal not required
Universal compatibility Larger size provides more humidification
Limited availability More parts required
$120 to $175
Regardless of whether a humidifier is integrated, built-in, or standalone, most models share the following characteristics:
Material composition: Virtually all PAP machine humidifiers manufactured today are made from thermoplastic.
Water requirements: As a rule, only distilled water should be used to fill humidifier chambers. Tap water can cause mineral deposits to form in the chamber; these deposits can damage the machine.
Chamber volume: The water chambers of most humidifiers will hold between 300 and 400 milliliters (mL) of water.
Adjustable settings: Some humidifiers allow users to adjust the level of humidification; additionally, most models offer customizable temperature settings (see next section).
Rainout reduction: ‘Rainout’ occurs when excessive moisture causes the air to cool as it passes through the connective hose; this can cause condensation to form, which affects airflow delivery and cause some of the health issues described above. A growing number of PAP machine humidifiers come with built-in rainout reduction systems that limit excess moisture and help prevent condensation (see ‘Care and Maintenance’ section for more information).
Next, we’ll look at key differences between heated and cold PAP humidifiers.
Heated vs. Cold PAP Humidifiers
Humidifiers fall into one of two categories based on their temperature settings:
Heated humidifiers feature a built-in heating element that warms the water in the humidifier’s chamber. The temperature settings can be adjusted for varying degrees of heat or, if the user chooses, no heat.
Cold humidifiers, also known as passover humidifiers, do not contain an element. Despite their name, these humidifiers do not actually cool the water; rather, the water is not heated and will correspond to room temperature. Cold humidifiers do not have adjustable temperature settings.
Heated and cold humidifiers may be integrated, built-in, or standalone. The table below looks at some key aspects of both humidifier types.
Cold (Passover) Humidifiers
Water chamber with built-in element
Water chamber with no element
Temperature can be adjusted
Temperature cannot be adjusted
$100 to $250
$50 to $90
Battery Life (DC Voltage)
8 hours or less
More than 8 hours
It’s important to note that heated humidifiers have higher satisfaction ratings among PAP therapy users. Warmer air is more comfortable to breathe in, most say, and users tend to experience less irritation. Those who use cold/passover humidifiers tend to experience more irritation and discomfort by comparison.
Care and Maintenance Tips for PAP Humidifiers
Now let’s look at proper care and maintenance guidelines for PAP humidifiers.
Tip #1: Use distilled water
Tap water contains a high concentration of hard minerals that can accumulate in the water chamber and eventually damage the machine. Additionally, breathing in these mineral deposits can lead to congestion and has been linked to more serious health problems, such as lung disease. Filtered, distilled water — which has lower concentrations of these minerals — is the best option, but bottled water will also be suitable.
Tip #2: Empty and clean chamber daily
The chamber should be emptied and cleaned in the morning after each use. This will help prevent mineral deposits from forming and extend the humidifier’s overall lifespan. Also be sure to empty the chambers completely before traveling with a humidifier; this will reduce the damage caused by standing water in the chamber; for airline passengers, this also ensures the humidifier will comply with regulations for bringing liquids on board.
Tip #3: Optimize bedroom settings to reduce rainout
As mentioned above, many PAP machines come with built-in rainout reduction systems. However, rainout may still occur even with these systems in place — especially if the humidifier is heated. To minimize the risk of rainout, be sure to do the following:
Increase your bedroom temperature: Bringing the outside temperature closer to the temperature of the water chamber helps cut down on condensation.
Make sure the hose is straight: Kinked hoses can obstruct airflow and trap moisture, which causes more condensation to accumulate. One way to prevent this issue is to align the machine with your bed and run the connective hose along the wall or over the headboard. PAP bed pillows, which have side cutouts to accommodate the hose and face mask, can also cut down on kinks.
Lower the temperature setting on the humidifier: This is the easiest way to minimize rainout, although it’s important to maintain temperature settings that are most comfortable for you. Also, please note this option is only available for heated humidifiers.
Insulate the hose: Condensation is likelier to occur when air heated with warm water begins to cool inside the hose. Insulating the hose with fabric can help the air maintain a consistent temperature, resulting in less condensation. Manufactured hose insulators are available, but DIY covers made from heavy fabric or cloth will also do the trick.
Consider investing in a heated hose: Heated hoses help the air remain warm between the PAP machine and face mask, thereby cutting down on condensation buildup. Take note: in most cases, heated hoses are only compatible with select models.
Important Considerations for PAP Humidifier Shoppers
When shopping for a new CPAP, BiPAP, or APAP machine humidifier and comparing different brands and models, here are a few variables to keep in mind:
What is your PAP machine humidifier budget?
Prices for humidifiers vary by construction and temperature settings. Both integrated and standalone humidifiers are usually priced between $100 and $160, while built-in humidifiers come with PAP machines (typically $400 or more). Cold or passover humidifiers tend to be less expensive than heated humidifiers.
How important are adjustable temperature settings?
Surveys have found that most PAP therapy recipients prefer heated humidifiers because they offer adjustable temperature settings and cause less irritation and discomfort. However, cold/passover humidifiers tend to be priced lower.
Do you have access to distilled water?
Distilled water is needed for all humidifier types in order to prevent mineral buildup and reduce the risk of congestion and other health issues. If you don’t have easy access to distilled water, then bottled water should be used instead — and this may affect your long-term budgeting for the machine.
Are you planning to power your PAP machine using DC voltage?
One notable downside of heated humidifiers is that they tend to drain batteries when the machine is powered with DC voltage. In most cases, the battery will need to be charged daily in order to provide at least eight hours of PAP therapy that night. Using heated PAP hoses also minimizes battery life. If you primarily power your machine with DC voltage or plan to travel with it, then be sure to stock up on batteries and inquire about charging options at your planned destinations.
Does the humidifier come with a separate warranty?
Most CPAP, BiPAP, and APAP machines are covered under some sort of warranty. The humidifier may be covered under the same warranty, or a separate warranty. Most separate humidifier warranties cover the product against defects for three to five years.