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: