On Humidity: Hard Data

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:

6 Responses to “On Humidity: Hard Data”

  1. AnnMarie Says:

    I’m confused by your statement that those who don’t have wood stoves use humidifiers. We have a wood stove and a monitor (kerosene) (and oil base board heatin which we try to not use). We use the monitor during the week in an effor to use us the kerosene we bought a year ago. The humidityy level is just fine. As soon as we start using the wood stove, we turn on the humidifier as it gets horridly uncomfortable. Even upstairs in the bedroom where it is cooler.

    Admittedly, we dont ever keep the house quite as warm with the monitor, but even when we crank it over 70 we are never as dry as when the stove is even going on low.

    I have been wondering how much electricity the humidifiers will cost us. But we cant uwe the wood stove without them. I was waking up in the middle of the night with such a bad sore throat i couldnt sleep. We do have a pot of water on the stove but it doesn’t produce much at all. So we run humidifier in same room as stove (primary living space, 24 hours running) and our bedroom (only while sleeping). We have the main area at about 35% humidity with this.

    House is from about 1980 and we just did Efficieny Maine so we shouldn’t have too leaky of a house. Things were never this bad in our 1900 house with a gas furnace either.

    • Cold House Journal Says:

      Hm. I can’t come up with any good explanation for why heating your house to a certain temperature with a wood stove should lower your humidity more than getting to the same temp with your kerosene heater. Actually, I can think of one: if the kero heater is the portable, unvented kind, then it would put out a lot of water vapor as a product of combustion. But I’m assuming the Monitor you mention is the sort that draws air from outside and vents directly to outside, too? If so then yes, I’m stumped. Do you have a data logger with which to document this phenomenon? : )

  2. AnnMarie Says:

    Yes, it’s the latter kind, not portable. No data loggers, but I think I will keep more of an eye on the humidity indicator when we go back to the monitor after the tree is down (the only good spot was right in front of the heater, so we are using wood all the time right now).

  3. Barelas Babe Says:

    Just stumbled on your website through a google search. We’ve been keeping our old adobe house at 57-60 degrees F in winter for years, but I want to learn more. Your site has been quite interesting and helpful – thank you for sharing your experiences.

    Re: humidity. The optimum level really surprised me, and I wonder if there is any difference for those of us who live year-round in desert climates (afternoon humidity here tends to be less than 20%) and those who deal with dry air due to heating. 40%-55% seems horribly humid to us here in the high desert southwest of New Mexico (at least that is when I notice many people complaining about the humidity). And this is anecdotal, I know, but my family also doesn’t seem to suffer from increased respiratory infections that I am aware of – a bad cold maybe once every 3-5 years seems to be our norm. Just thinking that perhaps just as we got used to colder indoor temps, perhaps our bodies have also adapted to drier climes.

    Now, we do go through bottles and bottles of lotion here!

    • Cold House Journal Says:

      Hm. Interesting. I’m sure that long-term exposure to low humidity could lead to adaptive changes, just as exposure to cooler temps does. But I just glanced through humidity data for the last couple months for Taos, NM and was surprised by how high the average humidities were. There is certainly a large daily swing, and often 45%, and mostly >55%. I imagine the daily swings are primarily a reflection of the dramatic day/night temperature difference out in the desert. Anyway, I’d be curious what your indoor humidity tends to be at this time of year, if you have a way to find out…

  4. Icerabbit Says:

    Humidity may be something we’ll track in the future.

    (imho) burning energy(electricity) to increase humidity is a waste. There are times when we feel less warm than other days at the same temperature and can only contribute it to higher humidity/ relative humidity, requiring a higher room temperature to feel warm. I have heard people talking about taking extra measures to increase humidity, because they’re convinced forced hot air and fireplaces dry out the air and make it feel colder … Where I think it is just the opposite, and that by adding humidity they decrease comfort levels or the apparant temperature? maybe those among us who live in a colder house notice this more? And in a warmer house higher humidity doesn’t change our temperature feeling / comfort as quickly? Do you have any experience and / or data in that regard?

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