Temperature fluctuations


  #1  
Old 10-23-02, 03:04 PM
Greta17
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Temperature fluctuations.....need help in sealing/insulating old house.

I've been reading several posts regarding insulation and moisture problems, and I was hoping someone would have a suggestion for me.
My house history:
- located in Dallas, TX
- House was built in 1939.
- Exterier is stone (Austin stone)
- attic has about 7" of blown in insulation
- Exterior walls have zero insulation
- all windows are original and are wood with single pane glass.
- house is built on pier and beam (so it has a ~ 2 foot crawlspace underneath that has vents to the outside).
- We have placed vent covers over the crawlspace vents.
- there is no insulation or vapor barriors in the crawlspace. Just the dirt ground, 2 feet of air, and then the floor joists.
- all windows and doors are sealed from drafts. We've done a good job of caulking and weatherstripping any gaps that we had.
- our heat is from a gas furnace and comes out of ceiling vents.

Problems:
1) condensation on interior of the windows.
2) when the heat is on, there is a huge temp. difference between top half of the room and bottom half. When you stand up, its about 85-90 degrees, but when in bed or sitting on the couch it feels about 60. If you lay on the floor, it's about 50 degrees. I'm not joking, the difference is that much.

What can we do to fix this problem? Replacing the old windows or having insulation put in the walls is not an option right now due to cost.
Is a radiant barrier the solution? In the crawlspace and/or attic?

Please help! Thanks for your time!
 
  #2  
Old 10-23-02, 08:46 PM
R
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There are basically 3 types of heat transfer, radiant, conductive and convection. Your description best describes convection. As the air in the home is heated it rises to the ceiling and as it cools it drops. Air that moves either up or down against an object, like your body or furniture, will leave heat if the air is warmer than the object or extract heat from the object if the air is cooler than the object. This is in essence convection heat transfer.

Conduction is the transfer of heat through an object. Your windows are a perfect example of conductive heat loss or transfer. All heat has moisture in it. On the outside of the window the temperature is much lower than inside the window. As the heat travels through the glass, the moisture in the heat condenses on the glass. A clear sign of conductive heat transfer.

Radiant heat transfer is the transferring of heat from one object to another without the use of a medium, such as air in convection. Radiant uses waves to transfer heat, example the sun radiates heat to the earth. It doesn't use convection or convection to do that. Any object that is warmer than its surroundings will radiate heat. Example is a pot used for cooking, the closer you put your hand to the side of the pot, the more warmth you feel. So the 2 main factors with radiant are the hotter an object is, the more heat that object will radiate and the closer you are to the warm object, the more warmth you'll receive from the object.

If we apply this to your situation, it is clear to me that conduction and convection heat loss are the reasons for your discomfort. The telltale signs are the large temperature differences from the ceiling to the floor and the condensation on the windows. Remember in convection, if the object (windows) is cooler than the air, it extracts heat from the air, making the air cooler and the condensation on the windows proves it. It is much cooler below the windows than above them. Hot air rises and cool air drops. Yet the temperature on the outside of the windows is still cooler than the temperature of the air at the floor. The reason for this is your heating system is replacing some of the heat that the windows are losing but is incapable of replacing the amount being loss per hour.

You don't have to take my word for it. There is a simple test you can do. Take a room and cover the windows in plastic. The next day if you have condensation on the rest of your windows, if you look in the room where you put plastic on the windows, there will be no condensation. Furthermore, the temperature difference between the ceiling and floor will be much lower than the other rooms and the temperature in that room will be higher than the other rooms.
 
  #3  
Old 10-24-02, 06:19 AM
Greta17
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Thank you very much for your detailed explanation as to the reasons for my problem. I vaguely remember some of these principles from my thermodynamics course in college! : )

Ok, so from what you are saying, I am rapidly losing heat thru my windows and my heater can't keep up with the heat loss. To fix (or help) the problem I can put plastic over my windows? My mom does this every winter in her home in Minnesota. Is this all I need to do or are there other measures I can take?

Thanks!

 
  #4  
Old 10-24-02, 09:15 AM
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Yes the simplest solution is to apply plastic to the windows. This is only temporary and there are some safety concerns with plastic on windows, especially if children are present. The plastic should be well secured to the window and as close as possible to the window.

You are also correct that the plastic on the windows will reduce the demand for heat in the rooms and the house. A fair estimate is approximately 25%. Besides the fact that it will reduce your energy bills dramatically, it will also increase the comfort in the home by reducing the temperature differences between the ceiling and the floor. And increase the humidity level in the air in the home, instead of it being deposited on your windows.
 
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Old 10-24-02, 06:25 PM
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I live in Wisconsin and use plastic every winter on the windows, it makes a huge difference. My heat ducts are located at floor level so I have the reverse of your problem in the summer-the cool air stays low, warm air high. By running my ceiling fans to distribute the air, through vertical movement, it is much more comfortable and helps my AC.
 
  #6  
Old 11-02-02, 07:38 PM
Mark B
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Greta17- That last post from schiejr tells you another thing you might be able to do. Install ceiling fans, if you don't have them already, and run them at low speed, in reverse. This pushes the warm air away from the ceiling down towards the floor. I have essentially the same situation that you have, regarding house construction and design, and the place is a drafty ice box in the winter (Colorado Front Range). My heat ducts are on the floor, but the lower parts of all the rooms are chilly within seconds of the furnace blower turning off after each heating cycle. Using the ceiling fans in the bedroom and living/dining area really helps to smooth out the 'parfait' effect. I also use plastic film on the inside of my windows, but am looking into replacing my wood sashes with sash replacement kits (double paned low-e glass and new vinyl jamb liners). Also, keep a bunch of sweaters around... ;-)
 
 

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