Archive for the ‘Humidity’ Category

On Humidity: Hard Data

January 3, 2011

In various holiday travels, I’ve stayed with friends, relatives, and in hotel rooms and observed the struggle against so-called “winter dry air”.  Some people have narrow buckets of water hanging behind radiators.  Some have kettles steaming on wood stoves.  Some who don’t have radiators or wood stoves have resorted to expensive electrical appliances that continuously spew steam into the air (which, as you can see, consume as much as 125W of juice, or up to 3 kWh of daily.)  The hotel room as simple dry as a desert– felt like something around 15% humidity.

I’ve discussed before how heat is the real cause of the air “being dry” in winter.  But your probably didn’t know that the data logger has also been recording Relative Humidity all along.  I haven’t been showing it, to avoid data overload.  But reviewing the data confirms what I already believed:  keeping the house cool keeps the air moist.  No need for fancy (or even simple) appliances that use even more energy to add extra moisture trying to make up for the dryness resulting from the burning of excessive energy in the first place!

Here’s a graph of last week’s humidity.  I’ll decipher: the purple line is indoor relative humidity (RH).  The dashed purple line is the average for the week: 45.4%.  The blue line is a rough graph of average daily outdoor RH.  And the faint red line, just for reference, is indoor temperatures.

If you look carefully, you might draw some conclusions.  As expected, all else being equal, raising the temperature lowers the humidity.  This is somewhat offset by our human behaviors, though– we tend to be cooking, showering, etc. during the same hours that the the wood stove might be running.  So sometimes the humidity and temperature go up in sync.  Mostly, though the moral is: if you keep the house cool, you won’t dry yourself out like a raisin.

Indeed, if you Google “ideal indoor humidity”, you’ll find most sources advise trying to keep it right about 45%.  Below 30%, you get increased risk of dry skin, respiratory infections, static electricity, and ozone.  Above 55% you have increased risk of condensation, fungus and mites.  Bacteria and viruses allegedly become more prevalent both above and below this range, as do risks of allergies and asthma.  Here’s a nice chart, based on this complex report from the Technical Resource Center of Finland:

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More Google Queries

November 9, 2010

A few Google queries which, it seems, landed people on this blog today:

Query:  “is 1.2 cord enough firewood”

Comment:  Oh, most possibly so!  If you live in a 400 sq ft house, it probably will be.  If you have hyper-insulated two-foot-thick walls and passive solar, it probably will be.  If you are only using wood as “ambience” heat to supplement fossil fuels, it probably will be.  And it just might be if you live with a house so chilly that most of your friends think you’re a little strange.  1.2 cords is about what I’m projecting we’ll use for the 12 months ending at Christmas… but maybe less?

Queries: “unhealthy cold house”, “bad health to have a cold house”, “cold house sick”, “respitory [sic] infections from cold house”

Comment:  Whoa whoa whoa.  Sure, a cold house can be unhealthy– if it’s saturated with radon, or asbestos, or rabies. But seriously, I’d be interested to hear any real evidence that a cold house is less healthy than a hot house for otherwise-healthy adults.  Hey, did you know that bed bugs’ reproduction, development, and feeding is hindered by cooler temperatures?  So much so that the state of Connecticut, in an official paper on how to counter the current bed bug plague, advises residents to “Keep bedrooms cool (if possible) at night to slow down bug activity.”  How about that!  (And one must ask– why not keep the bedrooms cool during the day, too??)

Query:  “humidity in bathroom doesn’t move”

Answer:  Uh… where where you hoping it would move to?  Akron?  Time for my annual plug for using a dehumidifier, rather than bathroom fan vent, in the winter.

Efficiency & Bathroom Humidity

January 27, 2010

Reader Frank recently commented:

“Another strategy that I’ve found useful is the proper use of the bathroom vent fan. I know the cfm rating of it and after figuring the size of the room determined that the fan is capable of completely exhanging ALL the air in the room in under two minutes! Excess humidity is no good either; the windows throughout the house frost up noticeably more when the fan doesn’t get used and interior humidity is too high. Anyway~ fan stays off during shower operations and gets flipped on for 1-2 minutes right after, and that’s it. Most of the humidity goes out, most of the heat stays in.”

This reminded me that I’ve been meaning to to discuss bathroom vents.  To start with my conclusion: unless you use them as Frank does (i.e., most judiciously) I think they are a horrible idea in winter.  They are the equivalent of cutting a hole in the wall and blowing cold air in through it at somewhere between 50 and 200 cubic feet per minute.  Oh, I know– they don’t blow air in, they blow air out.   But that air is replaced with air from some other part of your house… which is replaced with air straight from outdoors.  There’s no way around this fact.  You don’t really notice it, probably, because it’s sneaking in through a thousand cracks, and you’re likely in the shower while it’s happening.  But it’s a travesty.

In fact, it’s a double travesty, because besides replacing warm air with cold air, you are losing the (much larger) amount of heat contained in the water vapor.  One of my Cold House mottos is that water should leave the house in the same phase of matter (more…)

You’re Not Dry Until You’re Hot And Dry

January 15, 2009

Well, here we are: in the (statistically, on average) coldest week of the year here. And reality is keeping up pretty well with statistics. The high temp today was about 10F/-12C, and the low tonight is predicted to be around
-8F/-22C. Housemate has been ridiculously supportive of the minimal-heat concept. Since January 1 we’ve pretty much had the furnace switched on only from 5pm to 10pm, and set at 60-64F/16-18C.

It wasn’t quite as cold last night as it will be tonight, but it was cold enough for me to wake up about 4am and go looking for a hat (foolishly, I’d left them all downstairs.) We may leave the heat on a bit longer tonight.

Housemate, and many others, have expressed a concern that keeping the house cool will increase risk of respiratory infections during winter. I theorize that it’s just the opposite (barring extreme life-sapping cold): that keeping the house hot causes the humidity to go way down, drying out your mucus membranes and making you susceptible to infection.

Here’s a Q&A article from a Minneapolis newspaper. The writer first complains that his house gets unhealthfully dry in winter, so he bought a humidifier. But then he got ice on his windows and, presumably, a lot of moisture condensing on other cool surfaces (not to mention and increased electric bill). Woefully, he states he cannot afford new, better-insulated windows, which the newspaper had previously suggested for preventing condensation, and asks if there is any other solution.

The newspaper’s expert responds, “You have discovered one of the conundrums of living in climates as cold as ours. Research indicates that for health and comfort, a relative indoor humidity of 40 to 60 percent is desirable. But keeping the air that moist over the course of a winter is more than most Minnesota homes can handle.” He goes on to advise that the dryness problem can be ameliorated by “slow the infiltration of cold, dry air by caulking and sealing windows, doors and other leaking areas.”

“More than most Minnesota homes can handle”?? This is peculiar. You can easily keep your home this humidified, if you really want to. What you won’t be able to handle, though, is the mess it makes of your house if you simultaneously insist on keeping the indoors at tropical temperatures.

In fact, this whole answer is just phony. The winter air in Minnesota is cold, but in terms of relative humidity, it is not dry. In fact relative humidity is about 70% all winter long in Minneapolis. It’s 59% right at this moment. Going outside in this air will not dry you out, and letting it into your house will not do so either. What does dry you out is excessively heating this air, which causes it to be capable of containing much more moisture, which causes it to suck moisture from you. Air that is 50% humidity at 32F/0C will become just 16% humid at 68F/20C, and 12% at 76F/24C.

So, I argue the writer’s problem is probably not that he had too little moisture without the humidifier and too much with it, but that that his house was too hot at both times. Chasing a severely unnatural goal of a hot house in a frigid climate has left the writer with more problems (the “solutions” to which will create only yet more problems.) Nowhere in the expert’s “solution” does he suggest the logical first step of turning the thermostat down a bit. Because, I gather, that is a step backward into historical wisdom, rather forward into the glorious technological future.

It’s Not Winter’s Fault

December 14, 2008

I mentioned before that the complaints of “it’s too dry in the winter” may have more to do with excessive indoor heating than with actual climatic conditions. Here’s a graph of the Smallish City’s annual humidity pattern, which seems to confirm:

This shows that there is almost no seasonal change in afternoon humidities. There is a slight seasonal change in morning humidity (ranging from about 75% to 85%), but even this is not a clear winter/summer effect– it’s as humid in December as it is in June, and the least-humid month is actually April.

Right now, in spite of being 16F / -9C outside, we do have 73% humidity. Unfortunately by warming things up to 48F / 9F indoors here, I’ve lowered the humidity to about 20%, which is a bit dry. Still, I’ve had much less in the way of chapped lips, etc., this winter than usual. If I heated the house up to 68F / 20C, the humidity would be only 10%… parching.