How much does room humidity affect heat transfer/circulation throughout the house?

Higher humdity definitely helps.

Essentially when you add water to the air, you are adding more molecules. More moelcules in the air means more are colliding with your body per minute. The more that hit your body, the more energy (heat) transfers to your body. So most people feel more comfortable with higher humidity when temps are lower.

With a stovetop kettle, I can get the stove room's humidy up to 20-25%. I run a humidifier in the coldest room in the house, my kitchen, so that it can offset the lower temp some. Humidity there runs 50-60%. . . . . I think 60-70% is ideal in the winter, but not realistic unless you forgo wood heat and also run more than 1 humidifier.

What you are discussing is called either the "heat index" or "apparent humidity," and is exactly what a weatherman means when he is talking about the "heat index" on a hot summer's day.

Furthermore, your perceptions of the room temperature can also be affected by other items, including drafts and radiant heat. So, although your temperature may measure one way, your body may feel more radiant heat and thus feel warmer.

hfjeff said:

I picked some thermometers with humidity measurement and placed throughout the house. We are typically at about 16% with the insert running. The inlaws with the big Quad 5100i run a humidifier to keep the room humidity up around 50% and their house feels warmer even if the room temp is the same as mine. Is it all in our heads or is there really something to the humidity factor which makes the house more comfortable?

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Humidity makes a super big difference! Anyone who has spent any time in a dry climate, such as Arizona will feel it immediately when the drive to the East. For example, we spent several winters in AZ then usually went north before turning into Colorado. Turning onto I-70 we could begin feeling the humidity shortly into Colorado!

My wife is a frugal one and she dries the clothes using the heat from our wood stove. Talk about a difference on washing days! The humidity soars and if we don't turn the heat down, the sweat on our bodies soars too!

Anyway, raising the humidity only 10-20% will make a huge difference in your home.

I have seen it quoted that approximately 50% RH is a good target. Higher RH can allow for mold, mildew and dust mite growth, lower can lead to dry itchy skin, bloody noses, etc.

cozy heat said:

I have seen it quoted that approximately 50% RH is a good target. Higher RH can allow for mold, mildew and dust mite growth, lower can lead to dry itchy skin, bloody noses, etc.

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If you don't have a humidistat, a good gauge is a small amount of moisture around the edge of your windows when it is very cold out.... like when you take a shower.

As per mold and mildew, that is caused by uninsulated walls without a vapor barrier. If the heat with humidity escapes into a cold chamber it will condense into water. Not only will it promote mold/mildew but will also rot your home. Often you see older homes with paint peeling off the north side... well this is a major indication.

We like 40-50% RH and low 70's temp and it certainly feels great inside.

Here's a bit of info on regulating humidity levels in the house, shamelessly stolen from http://www.woodheat.org

Do wood stoves dry out houses in winter?
My wife and I are thinking of switching to a woodstove in our log house but I'm concerned about the inside of the house becoming too dry. I've heard stories about people with wood stoves whose furniture won't stay together and the woodwork splitting. A childhood friend's father used to put a pot of water on top of the woodstove to keep the air humidified. What's the real truth?
Cliff


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Hi Cliff,
Wood stoves are not specifically implicated, but do exhaust air from the house and this air must be replaced with air from outdoors, which in cold winter weather, is dry. Hence the theory that wood stoves dry out houses. Wood stoves are no different from oil or gas furnaces or any other device that removes air from the house. But a wood stove uses very little air; about the same amount as an inefficient bathroom fan. Compared to baseboard electric systems, yes they do contribute to lowering humidity, but not compared to all other options.

The real cause of low winter humidity in houses is leakiness of the house. Here's proof - new, tightly constructed houses need active ventilation systems in winter to control the build up of humidity produced by cooking, washing and breathing. Without active ventilation, the windows of a tight new house would mist up and run with condensed water vapor.

So, in old houses we humidify, and in new houses we dehumidify. All this has little to do with the heating system, except that a wood stove in a house does constitute part of the ventilation system. If you want higher humidity in your house in winter, spend some time and money on weatherization. On the other hand, there is no way you will ever get a log house tight enough to need active ventilation to control moisture.

Depending on several things, it can take over a week for your humidity to reach "equilibrium"- your furniture, floors, everything will absorb a bit of moisture.

Low humidity is bad for you, it's bad for your furniture, and it can zap computers fairly easily. I've replaced several very expensive terminals at work that were fried by nothing but static from a person touching them. We now have a huge humidifier there, and an alarm that pages me when it drops below 40%.

I like at least 40% humidity, just heard something on the news about low humidity and lung damage, yikes. If it gets real cold, you might have to adjust the humidity down, or the windows will frost up. But if it's in the 30* and up I have had the humidity up to 50%. It just seems like I can breath easier with the higher humidity. I have a big humidifier in my main house that used 5 gallons of water in a 24 hour period, just to keep the house at 40%. So you have to have a large enough humidifier, just like you have to have the right size stove for your home.

Very true that newly constructed homes are very tight and might not need a humidifier.

Lately in the northeast, the humidity has been though the roof (in excess of 90% the last 2 weeks) even during these cold snaps. I'm burning 24x7, and with a constantly refilled ceramic kettle (sometimes two!) I cant get the humidity in the house above 25%. Have several containers of standing water around the house that evaporate, but still cant get ahead.

Yes, it's normal for humid air at 75° F to "feel" warmer than dry air at 75° F.

There are several reasons, but one of the biggest is this: A cubic foot of air at 50% relative humidity has more mass than a cubic foot of air at 0% RH (due to the added mass of water vapor), so it requires more heat to raise its temperature a given number of degrees (in other words, it has a higher "specific heat" than dry air), and it "holds" more heat (in BTUs or calories) at a given temperature than dry air of the same temperature. What that means is that you have to take more BTUs *out of it* to cool it down a given number of degrees than you would with dry air of the same temperature.

There's also the "cooling evaporation" factor. In dry air, it's "easier" for moisture in your skin and lungs, etc., to evaporate, and that evaporation takes heat out of your body. The higher the relative humidity of the air around you, the slower this process occurs, meaning that your body gives up less heat per hour due to evaporation.

These principles also work in cold air: When cold air is very humid, it "feels" colder than dry air at the same temperature because the humid air weights a lot more per unit of volume (which means that it will have a higher "specific heat" than dry air), which means that it will "soak up" a lot more heat from your body before it begins to warm up than dry air at the same temperature. This is why it feels "raw" on a cold and rainy day near the ocean.