Sleep Apnoea Articles

CPAP Humidification and Rain Out

Unfortunately, some obstructive sleep apnoea patients using CPAP may experience nasal congestion and dryness of the nose and throat and this can compromise their acceptance of their treatment.

This dryness may occur if there is insufficient moisture in the the air flowing from your CPAP device. The problem can get worse in the UK’s colder months as we reach for the central heating controls which creates a drier home environment. Fortunately, this situation can be improved with the addition of CPAP humidification.

Heated humidification offers greater flexibility

There are two categories of humidification – warm and cold.

Cold or “passover” humidification consists of a water chamber that allows air from the CPAP to “pass over” the water before entering the CPAP tube thereby creating a humidified air stream. Although this set up is effective if you have low pressure CPAP settings or live in a warmer climate, it may not always be optimal as the air can become too cold for you to tolerate.

With a heated humidifier, moisture and warmth are added to the air delivered by your CPAP device. Because you can adjust the level of heat, heated humidification offers greater flexibility and may reduce your more severe symptoms. With the improved comfort, you’re also more likely to increase your treatment compliance and use your CPAP for longer periods.

In addition, if you suffer from hay fever in the summer months, a runny streaming nose and/or congestion, CPAP can exacerbate these symptoms. In these cases, heated humidification may also help to relieve your nasal irritation and aid your continued use of your CPAP.

CPAP ‘Rainout”

One of the problems that may sometimes occur with heated humidification is ‘rainout.

In cold weather, as the warmed, moistened air moves down the hose, it is cooled and can condense in the tube and mask. This is known as ‘rainout which can produce gurgling noises in your tube as well as water condensation on your face.

There are several ways to help reduce the risk of ‘rainout’:

  • Always have the device and humidifier positioned lower than the bed
  • Close the bedroom window, turn the humidifier down or raise the temperature in the bedroom at night, to lessen the difference between the room temperature and the hose
  • Tuck the tube under the bedclothes to keep it warm
  • Insulate the hose by covering it with a tubing wrap. Custom made ones can be purchased from ResMed or alternatively you can make your own by wrapping a towel, scarf, bubble wrap or aluminium foil around the tube

ResMed humidification solutions

If you have a ResMed AirSense 10 AutoSet™ device, an earlier ResMed S9 AutoSet, and/or an AirMini™ Travel device, find out more about the available ResMed humidification solutions here.

Or for more information, speak to one of the ResMed UK team on 0800 917 7071 or email

This blog post contains general information about medical conditions and treatments. It is not intended to be a substitute for professional medical advice, diagnosis or treatment. The information is not advice, and should not be treated as such. You must not rely on the information on this website as an alternative to medical advice from your doctor or other professional healthcare provider.

If you have any specific questions about any medical matter, you should consult your doctor or other professional healthcare provider. If you think you may be suffering from any medical condition, you should seek immediate medical attention. You should never delay seeking medical advice, disregard medical advice, or discontinue medical treatment because of information on this website. The views expressed on this blog and website have no relation to those of any academic, hospital, practice, or other institution with which the authors are affiliated and do not directly reflect the views of ResMed or any of its subsidiaries or affiliates.

6 thoughts on “CPAP Humidification and Rain Out

  1. Hi

    I currently have AirSense 10 AutoSet, along with ClimateLine Air and HumidAir.

    The question that I have is, when I use the ClimateLine Air, is it supposed to only heat up for less than 5 minutes ? I was under the impression that the ClimateLine Air was to stay heated throughout until the AirSense was turned off ?

    If it is to stay heated throughout the night then I’ll be happy to return back to my provided for either repair or a replacement.

    Vinod Patel

  2. Hi Vinod, please accept my apologies for the delay in responding. We have have had technical issue with the comments function on the site, but it is now fixed. I have spoken to one of the ResMed UK team and they gave the following answer:”The ClimateLine Air should gently remain heated through the night to help prevent the build of rainout (condensation droplets) which can develop as a result of warm humidified air running through the tube at night. It is normal to not feel the tube getting warm so many do think the tube is not heating when in fact it is. Therefore if you are not getting any rainout in the tube this would indicate it is working as expected. Also, if the tube is not working an error message will usually display on the AirSense”. If you’re still unsure, then please call one of the ResMed UK team on 0800 917 7071.

  3. I’m having a issue with my ResMed , I am using the auto feature on all settings as prescribed by the company that sold my machine. I did have a bad “rain out ” instance on my machine that I felt like I could have drowned in my sleep . Must have been 1/2 a cup of water in my tube. The machine was replaced right away by the company.
    The problems I am having now is my nose canal is now super sensitive and always itchy . Like my all my sinuses are going nuts for the last month. Yes I’m using the right distilled water . It seems like I’m very dehydrated at night and always wakes me up blowing major air through my very now dry canals . Not sure what is up, but last night I said I’m not using the machine , and the morning the flew Linda symptoms were not as bad. I’m linking the problems I’m getting to this machine. At the beginning it seemed good, but now after 6 months of use, I’m not having much fun at all. My sleeps are getting worse not better.

  4. Hello Nick, we’re sorry to hear of the issues with your treatment. So we can offer the best possible advice for you, it would be helpful to know exactly which model/make of device and mask you are using. Can you confirm this please?

  5. Within the UK we advise patients that using plain tap water is perfectly safe and acceptable, so long as any unused water is emptied in the morning and fresh water added again at bedtime. If you live in a hard water area this may result in lime scale deposits building up, so it is important you clean the humidification chamber regularly. We recommend avoiding descaling agents which can affect the seals and instead using a solution of one part clear white vinegar to ten parts water, leaving to soak for 20 minutes then rinsing thoroughly. We hope this helps.

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