Humidifiers: Friend or Foe? 

By Robin & Audrey Barrett,
Healthy Homes Consulting 

UPdate Fall 1995

     It is getting cold again and moisture problems that come with winter will soon be here.  Typically, if you have a tight house you have to worry about high moisture levels.  If you live in a leaky house or one with a high ventilation rate things can get too dry.  This issue we will look at what you can do if your house is too dry.

     In terms of human health, optimum levels for relative humidity range from 40 to 60%.  Unfortunately, the ideal levels for human health are not always the best for maintaining a house.  Levels low enough to prevent condensation and mould growth in most houses are usually between 30 and 50%, but may need to be lower in poorly insulated houses.  Problems caused by high humidity have been covered in previous articles.  However, before we start discussing humidification we would like to emphasize again one point about high moisture levels which contribute to mould growth: “PEOPLE SHOULD NOT LIVE IN MOULDY HOUSES!” (emphasis and Quote from the introduction of  “CLEAN-UP PROCEDURE FOR MOULD IN HOUSES” by Canada Mortgage and Housing Corporation).

     Problems from high moisture levels such as mould are normally obvious either by sight or smell.  Problems caused by low relative humidity are far more subtle and because of that often ignored.  Because cold air holds less moisture than warm air, if you bring in outside air in winter, either due to a leaky house a high rate of mechanical ventilation, your indoor air quality will likely be equivalent to the air outside in terms of contaminants, but it will be very dry.

     Low relative humidity can lead to chapped skin and lips, “scratchy” nose and throat, possible eye irritation and the drying of mucosal linings in the nose and throat which reduces your defence against viral and bacteriological infections (i.e. colds and flu’s).  In our climate it is not uncommon to see the relative humidity in houses during winter go down to the low thirties.  While this level is not ideal, it does not normally cause people undue discomfort.

     Levels from the teens to the twenties can cause significant human discomfort, problems with electronic equipment (due to increased static electricity), loosen joints in furniture and enlarge gaps in wood flooring and paneling due to the shrinkage of the wood.

     One of the classic solutions for the problem of dry air is a humidifier.  There are many types of humidifiers, but the most common include: Cool mist, ultrasonic, warm mist, steam, console (drum), and furnace.  Each has its own strengths and weaknesses.  Testing water samples in home humidification units for microorganisms has shown a mixture of bacteria, fungi, amoebae and protozoa (table 1).  The ability of these microorganisms to get dispersed into the air varies with the type of unit.  Cool mist and ultrasonic units have the capability to disperse many of these microorganisms into the air we breathe because of the type of mist they produce.  Warm mist, steam, console and furnace units produce droplets of water which are not as likely to transport living microorganisms through the air. 

     Unfortunately, living microorganisms are not the only water-borne contaminants we need to be concerned about.  There is also the problem of volatile chemicals which enter our breathing space by evaporation.  These include chemical contaminants in the water itself, such as chlorine, and chemicals produced by the growth of fungi or bacteria.  All types of units are capable of distributing these pollutants into our breathing space.

     The other problem with humidification is of course the moisture itself.  An incident comes to mind when parents asked if the black mould on the walls could be interfering with the benefits of the humidifier they were running in their child’s bedroom.  Although best intentioned the humidifier in this case was the source of a problem far worse than any benefit it created.  If you have mould due to condensation you do not want a humidifier.  Adding humidity will only make things worse.

What to do?
1. Make sure you really need humidification.  Your body may need it but your house may not be able to handle more moisture without having mould problems.  A simple check is to look for condensation on the coldest surfaces in the house (typically on windows and outside walls).  If you get occasional condensation but it never stays long enough to cause mould growth you are likely at the maximum humidity level that area of the house can stand.  If condensation stays for any length of time or you notice mould growth, dehumidification is what is needed, not humidification.  If your body needs more moisture but your house cannot tolerate a higher level without causing mould growth, it may be time to upgrade your windows and insulation.  The better insulated your house is, the higher you can keep the moisture level in the winter without having condensation and mould problems.

2. The quality of water used in the humidifier will have a large impact on the pollutants spouted into the air.  Distilled water is ideal, but whatever you use, remember that any pollutants in the water softener, dissolved minerals and metals) will end up in the air.  Cool mist and ultrasonic units have the capability of releasing most of the pollutants found in the water into the air.  Steam, console, and furnace units release far less of the biological pollutants, dissolved minerals and metals but they are still capable of releasing chemical contaminants such as chlorine or volatile chemicals produced by biological contaminants living in the humidifier water.

3. All types of humidifiers are capable of having microorganisms grow and multiply inside them.  Occasional cleaning is not effective in killing microorganisms but regular cleaning (at least once a month) with hydrogen peroxide should be effective.  Make sure this method is appropriate for your particular unit by checking the manufacturer’s instruction before attempting it.

4. The most important point is to maintain the humidifier properly.  If you cannot make a commitment to clean the humidifier regularly, it is better not to buy it.  The units mounted or furnaces are most often prone to problems because they automatically refill themselves, making it easier to forget about maintenance. 
In general, humidifiers are very useful devices to improve health or comfort in your home.  They are also potential sources of major health problems if improperly used.  Years ago, people would place a tray or pot of water on the back of a wood, coal or old stove and just let the water evaporate.  The pot was easy to clean, and if you forgot about it, it just went dry.  If you are going to use more modern technology, it is critical that you do it properly.