Humidity levels in your home are a big determiner as to just how healthy your home is. This page is a part of our discussion on Understanding water leaks, and moisture issues in the house and the impact of humidity of the health of your home– that is the impact of your home on the health of the occupants- human and pets.
How much moisture is in the air of your home? you can see the optimum zone in the diagram below. Many home is summer in Texas are around 85%. We all can become inured to humidity.
The chart below describes the stuff we do not like in our house or do not like to experience and the humidity ranges where these activities are most active.
You are not only uncomfortable with the humidity too low or too high, but these same uncomfortable conditions increase the likelihood of things like bacteria, mold fungi and dust mites flourishing. This diagram here is intended to give you a perspective on the role of humidity. We will actually address all these potential pollutants and go into much more detail with these issues when we talk about the healthy house.
Our purpose on this webpage is to get a hint as to the impact of humidity out of whack in your home…but to also understand the mechanism by which your home has a humidity problem.
We need to understand the fundamentals, because people try to baffle us with BS and get us to buy stuff that does not get at the roof causes.
Lets get our Bearings with the fundamental issue of too much moisture in North Texas homes.
North Texas is a humid place in the summer time. It might surprise you. It is not exactly the Mississippi delta, but check out the humidity curve on this page. The North Texas climate which is plenty hot is also humid.
We are going to cover the following points. I will state them first and then describe them in more detail. Air leaks into our homes and depending on the season, either adds moisture and humidity, or dries the air and reduces the humidity. The mechanism is air leaks and the inadequate handling of moisture air in our homes. We will address these issues in more detail as we proceed.
Moisture issues In the cooling season
Outside hot humid air leaks into our homes. When it mixes with our cool conditioned air created by our air conditioner, the humidity goes up. I will show you that with what is called a psychrometric chart.
Moisture Issues in the Heating season
In the heating system, cold outside air leaks into the house and as it warms up, it becomes capable of holding much more moisture. This because warm air can hold much more water vapor than can cold air. This drops the humidity level in the heating season to below what is comfortable and bow what is optimal. YOu might want to look at the chart above to see the effects of air that is too dry in the home, or when we address healthy homes later in this collection of pages. Many people humidify in the heating system. This is treating the symptom. The low humidity is a symptom. The cause is the cold air leaking in.
Ok there is it. Humidity problems in homes start with air leaks.
You might have some mechanical issues too, and we address HVAC issues here– and we talk about issues with fans in your house here. but air leaks are a root cause. The real solution is to stop the air leaks, and stop the fundamental problem with humidity. We will have a comprehensive discussion of solutions late, but lets get through our basic understandings of the fundamental issues involved.
We will address air leaks later but we have to connect the dots with humidity and the nature of moisture.
In a bit we get to look at something really exciting- the psychrometric chart- but we do need to review a few points first for perspective and reference points.
Lets Review the basic nature of Water.
I am sure you remember this from school, so we will just review it briefly.
Water freezes at 32 degrees F- under conventional conditions and air carries water as a gas. How much moisture it contains depends on the temperature of the air. Absolute humidity is 100% – and any surface cooler than dewpoint will collect condensation.
The actual amount of water in the air at 100% humidity depends on the temperature. Air at 80 degrees at 100% humidity is actually holding more water vapor than air at 60 degrees and at 100 % humidity. Relative humidity is the percentage of water in the air as a ratio to the level of absolute humidity of that temperature of air.
As temperature of air goes up, the relative humidity goes down unless you add more moisture to the air. As temperature goes down, relative humidity goes up. Any normal surface colder that the dew point of the air will collect moisture as liquid water. This is like dew on the grass in the morning- or your cold glass making a water ring on paperwork on our desk or just your desk, if you are a cleanliness nut with an uncluttered desk.
These relationships are not linear. Air at 80% does not necessarily carry twice as much water as air at 40 degrees. This is where the psychrometric chart comes in and this chart is a bit confusing- let take a look at the chart.
The psychrometric diagram looks a bit confusing but with some simple points of reference it reveals why homes with conditioned air can by muggy and uncomfortable.
The curved lines are humidity levels and the bottom X axis running across the bottom fo the image is temperature. Let pick a point that relates to the average dewpoint in North Texas in August 2014 – about 70 degrees.
So find the 70 degree line and follow it up until you hit the highest curve that is dewpoint 100% humidity. Now take that line horizontally- which means the same amount of moisture in our parcel of air, we are just raising its temperature. Lets take the temp up to 100F which is not a stretch for North Texas. Here the relative humidity is only 40%.
When this hot air leaks into your house, and your air conditioner cools it down, you have brought in a lot of moisture. Now I am not going to get into grains of water per pound of air or anything, but depending on how much your house leaks- depending on how many times per hour the air in your home is exchanged with the outdoors because of leakage- you are picking up a lot of moisture.
You HVAC system must handle this moisture well. And so we return to the question that we broached at the start of this page. What do you think is the humidity level in your home? Does it feel humid? Muggy? Is the air too dry in winter?
OK, now we are ready to talk about air leaks- how all that humidity gets inside.
Homes leak air. The hot humid air of summer settles in through the ceiling because of pressure differences in the house. In the heating season warm air floats up and out of the ceiling. We talk about all things air leaks here.
Excess levels of moisture and humidity are required to grow mold.
You saw it in the chart at the top of the page. Mold and Mildew have a range of requirements for robust growth. We want to make sure we do not provide these in our homes.
We talk about Mold Issues in more specific detail here.
So what should you do about air leaks and moisture issues? We will talk about solutions after we get all our pieces together.
Any questions or comments, or experiences you would like to share… feel free to add them below.