Why’s the air so dry in the winter?

Do you ever wonder why your skin cracks and dries out in the winter? Why you get nosebleeds and sore throats? Why you can see your breath when it’s cold out? It all comes down to physics!

Tell Me Why I Can See My Breath When It's Cold

The air can only hold a certain amount of water and the colder the air, the less water it can hold before the water condenses. When you exhale, your breath is warm and contains lots of moisture. As your breath cools down, it eventually reaches a temperature where the air can’t hold all the moisture and you see a fog.

You’ve probably heard the weather forecaster talking about the “relative humidity” (also called RH) of the air. It’s relative because it depends on the temperature outside. For example, if it is 20F outside and the relatively humidity is 80%, when you take that air, bring it inside and warm it to 70F, that same air will only have a relatively humidity of about 15% – very dry indeed!

So during the wintertime, even if it’s very humid outside, when that air comes into your home and warms up, it is very dry air. And dry air wants to suck the moisture out of your skin, leading to chapped lips, nosebleeds, and generally uncomfortable living conditions.

Interestingly, in a normally sized home, overly dry inside air is also a giveaway of a leaky house because most homes have a fair amount of moisture from internal sources – people and pets breathing, watering plants, showers and cooking. All of these dump moisture into the air. In a tight house, this would be more than enough moisture to keep things comfortable in your home. But in a leaky home, the moisture is leaving through all the cracks and the really dry outside air is coming in creating a double whammy that dries out your home.

So if you have dry conditions inside your home during the winter, the best thing you can do is to tighten your home so that less warm, moist air leaves. This could involve getting better windows or putting that shrink wrap plastic over your windows. You can also tighten your home by fixing doors so they seal better. But one of the biggest culprits of air leaks result from poorly sealed ducts. I’ve even seen homes where there were ducts detached in the attic, so the furnace was blowing lots of warm, moist air right out of the house! Problems like this cause the snowmelt seen in my earlier posting.

Keep in mind that air leaking out of your house means an equal amount of cold, outside air is leaking in, and that air has to be heated. So if you seal your ducts and other air leaks, you’ll be reducing your utility bills and making your home more comfortable.

How much of a difference can this make? Easily 30% of your heating bill comes from having to heat cold air that comes in through all these cracks! In fact, studies have shown that air sealing your home can provide the best bang for your buck – making your home more comfortable and energy efficient.

So next time you’re wondering why it’s so dry in your house, go looking for the air leaks. Fix those and you’ll have a more comfortable and energy efficient home!