What is the purpose of humidifying air?

In the last post, I said my next post would be to compare central to portable humidification systems.  Well, I got well into writing that post–which will be more than one post, as I found out–when the thought came to me that maybe I should explain some of the reason I have heard for humidifying our homes.  That last post indicated one reason based on more recent research and that is to control virus. We shall see if future research supports the findings.

Another common reason I heard is to protect the wood in a home.  I am not so convinced, at least for more modern homes that use a lot of manufactured wood products rather than the real McCoy (do people still use that phrase?).  All wood expands and contracts as the wood’s moisture content changes, and the content does change with the amount of moisture in the air.  Cracks form in the wood when it is constrained from moving either by the way it is installed or by its own natural structure.

 

Based on a little research (and note I said a LITTLE research) I believe that most wood in homes expands less than 1/4″ and more likely the amount is around 1/8″.  In a short article published on-line (http://www.forestry.uga.edu/outreach/pubs/pdf/FOR93-034.pdf), The University of Georgia Cooperative Extension Agency published results of a little study on the amount of moisture in wood in 20 homes or offices for oak and maple.  The authors found that the average maple moisture content 7.9 to 10.3% and for oak the average was 6.3 to 8.1%.  In another article published on-line  (http://www.thisiscarpentry.com/2010/09/03/moisture-content-wood-movement/), Mr. Carl Hagstrom gives this rule of thumb:  for every 4% increase in wood moisture content, the wood expands 1% (for “flat gain material”).  (Mr. Hagstrom also very nicely provides a link to an on-line shrinkage calculator at http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkage.)  Putting these two bits of information together, wood inside homes will likely expand about 1% during a typical change in winter conditions.

Mr. Hagstrom further states that wider boards expand more than narrower boards, as you would expect based on his rule of thumb.  However, not a lot of wider boards are used in new construction.  Not that many old big trees are still around these days, and those that are usually are used for veneers.   But, craftsman builders know how to account for wood expansion–both back then and now.   Having inspected a large number of older homes, I have not seen a lot of cracks in finish wood.  I have seen plenty in structural wood, although not many I would consider bad enough to be structural issues.  At that, I have to wonder if the cracks were not caused by the wood not being adequately dried or being exposed to the more extreme variations in moisture and temperature of outdoor air.

I also do not hear many homeowners saying that they humidify because of concerns about the wood.  Instead, the issues are usually that pesky static shocks from walking across carpets in dry environments and physiological issues such as stuffy head and dry skin.  WikiHow has a list of things a homeowner can do to reduce static shock (http://www.wikihow.com/Remove-Static-Electricity).  Apparently, some carpets are also now manufactured to reduce shock.

I have my own theories about the physiological effects of dry air.  I believe that the dry air dries out the mucous membranes of the nasal system.   To prevent drying, the the mucous membranes swell to increase humidification of the air going into our lungs.  Swelling of the membranes causes little fissures in the mucous membranes that cause slight bleeding, which some people see when they blow their nose during this time.  The nasal stuffiness causes some people to use decongestant sprays that can also irritate the mucous membranes and some have rebound effects that make the stuffiness worse.  Decongestants , particularly the ones combined with antihistamines, can also cause a drying effect of the membranes.  Moisturizing sprays can help relieve the drying effects; but, the effect, for me at least, is relatively short-term.

I have one other alternative to help reduce the physiological effects of dry air that most people will not find attractive.  That is, reduce the air temperature of the home.  Doing so will effectively increase the relative humidity of the air.  I confess that during the winter, I keep my home at around 65 degrees.  Even though this temperature is noticeably lower than the 75 to 85 degrees most people keep their homes at during the winter.  I have found over the years, that our bodies are amazingly adaptive.  One other lesson I have learned is that I can always put on more clothes and putting a heating pad under my butt during the coldest days can go a far way toward keeping me warm enough.

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