Btu Buddy 114: Excess Humidity in a House
Now, Bob’s company has promoted him to help train a new employee, right out of a school specializing in HVAC, just like Bob was. Bob is now Tim’s Btu Buddy. Tim is anxious to travel with Bob. Tim realizes that he is right out of school, with the theory and lab work that he accomplished in school, but still needs help. He knows that he worked with many of the components of the systems in the school, under ideal conditions with good light and air conditioning. Now it is into the field, sometimes under the house with poor lighting, or out on the rooftop in the sun, where the real action is. He is naturally and normally reluctant, but he has Bob to help guide him.
Bob and Tim were on their way to a residence outside of town where the homeowners’ complaint was excess humidity in the house. When they arrived, they met the housewife and she told them, “This house has too much humidity. The plumbing fixtures often sweat, there is mold in some of the closets, and mold is beginning to form in the laundry room.”
Bob and Tim took a look around. After crawling under the house and examining the structure, Bob told the owner, “I found the following things that will reduce the humidity in the house:
1. The house is at the bottom of a slight slope and water from up the slope can run down against the foundation and seep under the house in rainy weather. You should have a small ditch or mound on the upper end of the house to stop the rainwater from getting to the foundation.
2. The gutters are full of leaves and probably running over during rains, again, allowing water to get up next to the foundation. You can see where water has run over the gutters and has been running down the side of the house. You need to have them cleaned and be sure that they are maintained.
3. The earth is not covered in the crawl space under the house. A good quality plastic sheet could be spread on the ground under the house to keep any moisture that is in the soil from rising up and adding moisture to the house.
4. The dryer vent is partially plugged and most of the moisture from drying clothes is coming into the house. We can take care of that for you.
5. We noticed that you have a partially open window in the den, probably because of smokers. That open window will allow a lot of outside air into the house. We would recommend an electronic room air filter for that room instead of opening the window. A whole house electronic air filter would be even better. We can give you a price on that and it would be a great fix for the whole house.
6. We will check that air conditioning unit to make sure that it is doing a good job and removing as much moisture as it can.
7. Your home is not on city water, so you are using a well. Well water is much cooler than water from the city water main. Excess humidity in a house can easily cause the entering plumbing pipes as well as the sink drains and toilet bowls to sweat. We are going to see what we can do to dry the structure out with the cooling unit and then maybe the humidity will be low enough to stop that sweating.
8. The mold that you have seems to be very slight at this time. You will need to clean those areas with the proper mold killing cleaner and I believe we can keep the mold out with a lower humidity.”
“Wow”, said the owner, “I didn’t realize that any of these things could cause humidity problems. We have only lived in this house for several months and it didn’t seem to have any problems.”
Bob said, “These things kind of creep up on you before you know it. A home is constant maintenance. That is why some people live in condos and apartments where the maintenance is taken care of by others. It is a big responsibility to own a properly maintained home.”
The owner said, “We seem to stay busy and don’t notice the small things. I will make a list of these things and keep it posted and try to keep up with them.”
Bob said, “Moisture is an enemy of a wood structure. The structure must remain dry or it will deteriorate over time. We are going to check out the cooling unit now.”
Tim said, “I didn’t want to appear dumb in there and ask this question, but, how come the humidity change makes such a big difference?”
Bob responded, “No question is dumb. Dumb is not finding out answers to your questions. All of this is related to the dew point temperature of the surfaces in the house. You studied the dew point temperature in school, but it is one of those subjects that is not very interesting, but important. The dew point temperature is the temperature where moisture will begin to form on a surface. Imagine if you set a glass of water out on the table in a room and very slowly started adding small amounts of ice to the glass and stirring it all the time. As the surface temperature of the glass began to lower, at some point, moisture would begin to form. The surface temperature at that time is the dew point temperature (Figure 1).”
Tim said, “I remember that, but I never thought it would come into play.”
Bob said, “The fact that the plumbing was sweating and mold was forming proves that the dew point temperature is too high in this house.”
Tim asked, “What should the highest dew point temperature be?”
Bob said, “Good question. Cooling equipment is rated at an indoor temperature of 75°F at 50 percent humidity and a dew point temperature of 56°. Most people would prefer a cooler temperature and would like to control the structure at about 72° and about 50 percent humidity, which would be a dew point temperature of 52° (Figure 2). Well water temperature in this area would normally be about 58°; so at a 72° thermostat set point, the dew point temperature must be above 56°. Let’s measure it and see what it is.”
They used an electronic psychrometer (Figure 3) and found the indoor temperature to be 73° and the dew point temperature to be 63°, which is a humidity level of about 70 percent. Bob said, “That is too high and will cause problems.”
Bob and Tim proceeded to check out the cooling unit and found that the condensate drain was not draining and was spilling out under the house, causing even more moisture. They connected their wet vacuum to the drain outlet and turned it on and pulled a big plug of algae out of the line. They then added an algaecide tablet to the line trap to help reduce the algae in the future.
They checked the unit performance and found it to be good.
They reported to the owner what they had found with the drain and told her the following: “We are going to assume that you will take care of the items we mentioned earlier, and after you have completed the list, please call me a week later and tell me what you see. I think the first place you will see a difference is in the sweating plumbing fixtures. When they stop sweating, I think the job will be complete.”
Tim later asked, “Why did we use the shop vacuum instead of blowing the line out?”
Bob explained, “If you blow the line from the outside towards the coil, you will blow that plug back into the coil pan. It will drain for a while, until the plug floats back over the drain pan drain hole. When you pull the plug out, you get rid of it.”
The owner called back in about three weeks and reported that all the work had been completed the week before and things looked good. There were no more sweating fixtures and the overall humidity seemed to have dropped to a good level.
Tim said, “Wow, what a fix, and all of it was just common sense, not a big mystery when you understand it.”
Bob said, “As time goes by, you accumulate a knowledge base from the experiences you have. Always try to remember these basics and apply them.”
Publication date: 9/17/2012