by Don Ames, www.detectenergy.com
Heat flows out of your home in two ways, transmission and air leakage. Transmission and air leakage occur through all surfaces of the home - walls, floor, roof, windows and doors.
The amount of heat transfer depends on two factors: thermal resistance and surface area. Thermal resistance has to do with the quality and quantity of the material in the walls, floor, roof, windows, and doors.
Surface area has to do with the size of the home and the size of the holes in the home. There are two other factors that influence the amount of heat loss and, of course, the size of the heating bill: temperature difference and pressure difference. The greater the temperature difference between inside the home and outside the home, the more heat transfer will take place through the structures of the home.
Also, the greater pressure difference between inside the home and outside, the more heat will leak through the holes in the home. In most cases, pressure difference is caused by wind hitting the home. Windows are a special concern because of the low thermal resistanceand the significant surface area. Doors have less associated overall energy loss because thermal resistance is greater and surface area is small.
Insulation is important because it resists the flow of heat. Insulation in a wall cavity forces the heat to conduct from one insulation fiber to another and through one air pocket to another which slows the passage of heat.
A materials heat conductivity describes how much heat flows through a 1-inch thick by 1-square foot slab of a material in a hour when there is a 1 degree difference in temperature from one side of the material to the other side. Heat conductivity, denoted by the letter K, allows us to compare how well common building materials conduct heat.
Aluminum is the most conductive common building material. Air, as it turns out, is one of the poorest conductors of heat. Here are some common building material and their associated K values. The lower K value the better.
Aluminum - 117 K, Steel - 26 K , Glass - .65 K, Concrete - .48 K, Brick - .36 K, Wood - .13 K, Rubber - .12 K, Glass Insulation - .02 K, Air - .015 K.
Therefore, as homeowners and utility payers, we begin to see and understand how our homes work and how the heat gets away from us and ends up costing us more money to keep warm. To control heat loss is to control our power bill. Here's some things you can do.
1. Limit heat loss through windows by air sealing the connection between the window frame and the wall.
2. Install insulated window curtains to increase thermal resistance.
3. Replace single pane windows with new double pane windows.
4. Install plastic window covering or storm windows.
1. Go on a draft finding tour of your home. Use the smoke from an in-scents stick to help locate air leakage.
2. Fill holes and cracks with caulk or insulating foam.
3. Air seal the attic floor and air seal the floor between the indoor space and the ground. Caulk or foam all wire, pipe, and heating duct penetrations.
4. Construct a wind barrier in the yard. Plant a row of trees or bushes that will protect the windy side of the home.
1. Air seal all penetrations and install generous layers of insulation.
2. Identify your homes air barrier. This is the solid barrier that separates the outside air from the inside air. Think of it as the barrier that keeps the wind out.
3. Identify your homes thermal barrier. This is the layer that resists the passage of heat. Think of it as the insulation barrier.
4. Establish a complete thermal barrier and a complete air barrier. Have both barriers on the same plane, in the same place and touching each other.
5. Maintain the integrity of the homes shell by protecting the thermal barrier and the air barrier with a good roof and a good exterior paint job.
Like changing the oil in your favorite car, your home will perform better and cost you less with regular improvements and routine maintenance. With an understanding of how your home is constructed and how your home can perform better, you can provide retrofit upgrades that will keep heat transfer at a minimum and that will keep you warmer for less money.
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