Humidify or Dehumidify?
by Building Inspector and Indoor Air Specialist, Dan Schilling
© Copyright 2002 Residential Inspections LLC, All Rights Reserved
The Old Way of Thinking
Old homes used to lose a lot of heat, and along with the heat loss was the loss of humidity. During cold weather, the indoor air would become so dry that people would use portable humidifiers, or have them permanently installed on their furnaces. These humidifiers solved the lack of humidity but have lead to other problems in homes, usually related to lack of maintenance. The built in humidifiers were out-of-site and therefore out-of-mind, and the portable models were also a chore to clean and sanitize. As a result, humidifiers would grow bacteria and mold inside of them, which caused sickness due to biological contamination of the indoor air. The common term for this sickness is “humidifier fever”.
To compound the problem further, homeowners believed that if they had a humidifier, they must need to use it, albeit they paid little attention to the actual humidity levels in their homes. As a result, humidity levels would often exceed the recommended maximum level of 50% and consequently cause biological problems indoors with exploding dust mite populations in furniture and carpet, and mold contamination throughout homes. Furnace mounted humidifiers would also back-up and leak into furnaces causing corrosion and mechanical damage. Humidifiers would also produce white dust around a home depending on the mineral or sodium content in the water.
The New Way of Thinking
Newly constructed homes rarely have need for more humidity; in fact, the exact opposite is more likely and a dehumidifier is usually needed, sometimes even during the coldest winter months. This is due to the high moisture content of brand new homes. Similarly, homes that have had energy conservation measures performed no longer have the need for humidification. This might include the addition of attic insulation, new windows, caulking, weather-stripping, newer furnaces, etc. All of these measures turn old homes into new homes from the humidity perspective. Because moisture travels with heat, when you save heat, you save moisture by default, and would likely do yourself and your home a disservice by using a humidifier. Indoor humidity levels in homes today will rarely ever drop below the recommended minimum level of 30%. In most situations, home inspectors will recommend removing humidifiers when installed on furnaces due to the health issues and mechanical damage they cause. There may be unique situations in which added humidity might be a necessity, but they are rare. In these situations, it would be best to simply use a small portable unit that can be easily cleaned and monitored.
When dehumidifying, it is important to have a dust screen over the area where the air enters the dehumidifier in order to keep the inner coils clean. When clogged, the unit will operate poorly, waste electricity, and may cause the coils to ice up and stop functioning altogether.
Finally, people cannot simply depend on a sense of feeling to determine if the indoor humidity levels are proper. Humidity levels could well exceed safe indoor levels before ever being perceived through the senses by building occupants. Perhaps the most important thing you can do is to monitor your indoor humidity levels all year long with a humidity gauge. If you do not have one or question whether the one you have works properly or not, purchase a new humidity gauge for your home and use it faithfully.
with those you care about.