CPAP Rainout: Why Water Collects in Your Tube and How to Fix It

What Is CPAP Rainout?

Rainout is condensation that forms inside your CPAP hose, collecting as water droplets that gurgle, splash, or drip onto your face during the night. It is one of the most common and most frustrating CPAP complaints, and it has nothing to do with a malfunction. Your machine is working correctly. The problem is simple physics.

Why It Happens

Your CPAP humidifier heats water in its chamber and adds warm, moist air to your pressurized airflow. That warm, humid air then travels through your hose to your mask. If the hose is cooler than the air inside it, the moisture in the air condenses on the inner walls of the tube, exactly like water droplets forming on a cold glass on a summer day.

The bigger the temperature difference between the air inside the hose and the outside of the hose, the more condensation forms. This is why rainout is worse in certain conditions:

• Cold bedroom. The most common trigger. Keeping your bedroom at 65 degrees F while your humidifier pumps out warm, moist air creates a large temperature differential.
• High humidity setting. More moisture in the air means more water available to condense.
• Tube running along a cold surface. If your hose drapes over the edge of a nightstand, rests against a cold wall, or hangs near a window, those cold spots accelerate condensation.
• Air conditioning or a fan blowing on the tube. Moving cold air across the outside of the hose cools it rapidly.
• Winter months. Indoor heating dries the air (making you crank up humidity) while bedroom temperatures drop at night as the heat cycles off. The combination is a rainout recipe.

Solution 1: Heated Tubing

This is the most effective solution. A heated tube maintains the air temperature throughout the entire length of the hose, preventing the temperature drop that causes condensation. The air arrives at your mask just as warm and moist as it left the humidifier.

For ResMed AirSense 10 and 11 machines, the ClimateLineAir heated tube (opens in new tab) integrates directly with the machine's climate control system. When connected, it enables Climate Control Auto mode, which adjusts tube temperature and humidity together based on room conditions. You set a target comfort level, and the machine handles the rest.

Most people who switch to a heated tube eliminate rainout completely on the first night. It is the single best investment for CPAP comfort after getting the right mask.

Solution 2: Hose Covers and Insulation

If you are not ready to invest in a heated tube (or want an extra layer of protection), a CPAP hose cover (opens in new tab) wraps around your standard tubing and insulates it from the room air. Think of it as a tiny sleeping bag for your hose. The fabric barrier slows heat loss, keeping the air inside warmer for longer.

Hose covers are inexpensive (typically $10 to $20 as of March 2026), reusable, washable, and work with any standard 6-foot CPAP hose. They do not eliminate rainout as completely as a heated tube, but they reduce it significantly, especially in moderately cool bedrooms.

Solution 3: Tube Positioning

How your hose is routed from the machine to your mask makes a real difference. Gravity pulls condensation toward the lowest point in the hose, and you do not want that low point to be near your face.

Best practice: Route the hose so it runs upward from the machine to your mask. The machine should be at the same level as or below your bed. If your nightstand is higher than your pillow, water runs downhill toward your face. Put the machine on a lower shelf, on the floor, or on the nightstand with enough slack that the hose arcs upward.

A CPAP hose hanger (opens in new tab) clips to your headboard or nightstand and suspends the tube above you. This keeps it off cold surfaces, prevents kinking, and ensures that any condensation that does form runs back toward the machine rather than into your mask.

Solution 4: Room Temperature Management

Since rainout is caused by a temperature differential, narrowing the gap between your room temperature and your humidifier output reduces condensation:

• Keep your bedroom above 65 degrees F. If you prefer a cool room for sleep (many people do), a slightly higher temperature in the 67 to 70 degree range eliminates a lot of rainout.
• Move the CPAP away from cold walls, windows, and vents. Cold air flowing over the machine or the first section of hose can cool the air before it even gets into the tube.
• Close nearby windows in winter. Even a small draft across your nightstand can cool the hose enough to trigger condensation.

You do not need to make your room uncomfortably warm. Even a 3 to 5 degree increase can make rainout disappear.

Solution 5: Adjust Humidity Down (Carefully)

If the other solutions are not practical, reducing your humidity setting by one or two levels decreases the amount of moisture available to condense. Less moisture in the air means less water in the tube.

The tradeoff is obvious: less humidity may mean more dryness. This is why heated tubing or insulation is the preferred approach. They let you keep humidity high while preventing condensation. But if you are currently running your humidity at 7 or 8 and experiencing severe rainout, bringing it down to 5 or 6 while adding a hose cover may be the right balance.

For a detailed guide on finding the right humidity level, see our article on CPAP humidity settings.

Why Rainout Is Worse in Winter

Winter combines all the worst factors for rainout:

1. Cold bedrooms. Heating systems cycle off at night, and bedroom temperatures drop.
2. Dry indoor air. Heating systems dry out the air, making you crank up the humidifier to compensate.
3. Cold surfaces everywhere. Nightstands, walls, and the hose itself are all cooler.

The result is a large temperature differential between the warm, moisture-heavy air in your hose and the cool environment around it. This is why many CPAP users who never experience rainout in summer suddenly deal with it every November through March.

Seasonal adjustments are normal. You may need to increase tube temperature or add a hose cover in the fall, then back off in the spring. Your machine is not broken. The physics just changed.

How Rainout Affects Your Therapy

Rainout is primarily a comfort issue, but it can affect therapy in a couple of ways:

• Waking you up. Cold water splashing on your face at 3am will wake you up, and if it happens repeatedly, you may take your mask off and skip the rest of the night. Reduced usage time is the biggest threat to effective therapy.
• Mask seal disruption. Water pooling inside the mask can break the seal, increasing leak rate. Your machine compensates by increasing flow, which can cause more events.
• Increased cleaning needs. Standing water in your hose creates an environment where bacteria and mold can grow. If you are experiencing rainout, pay extra attention to your cleaning routine.

Troubleshooting Persistent Rainout

If you have tried the solutions above and still have water in your tube:

Check your tube for damage. Small cracks or holes in the hose can let cold air in and cause localized condensation. Hold the tube up to a light and look for visible damage. Replace damaged tubing promptly.

Check the humidifier chamber seal. A chamber that is not seated properly can leak warm air around the seal, reducing humidity delivery efficiency and causing the machine to overcompensate.

Verify your tube type in machine settings. If you are using a heated tube but your machine thinks a standard tube is connected, it will not activate tube heating. Check the settings menu on your machine to confirm the tube type matches what is physically attached.

Make sure Climate Control Auto is enabled. On the AirSense 11, Climate Control Auto coordinates the humidifier and heated tube together. If you manually override one but not the other, they may work against each other.

Checking Your Data

After making changes to combat rainout, your leak rate data is the best indicator of whether things improved. Import your SD card into CPAP Clarity and compare leak rate charts before and after your changes. A drop in average leak and fewer leak spikes overnight means your seal is better, which is often a downstream effect of eliminating rainout and the disruption it causes.

When to Talk to Your Provider

Rainout itself is a comfort and equipment issue, not a clinical one. But consult your sleep physician or equipment supplier if:

• Rainout is causing you to skip therapy nights. Adherence problems are always worth discussing.
• You suspect your pressure or humidity settings need a broader adjustment. Your provider can review your data and make changes that address both comfort and therapy effectiveness together.
• You notice unusual smells or visible mold in your tubing or chamber despite regular cleaning. This needs immediate attention.

The Bottom Line

Rainout is physics, not a malfunction. Warm, moist air plus a cool hose equals condensation. A heated tube eliminates the problem for most people. If a heated tube is not in the budget, a hose cover, better tube routing, and a slightly warmer bedroom will get you most of the way there. Adjust your humidity and tube temperature by season, keep your equipment clean, and check your data to confirm the fix is working.