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NORA Advanced Efficiency

National Oilheat Research Alliance 37 insulated (The insulation can be outside the foundation or inside.) Figure 9 above. Materials that could be damaged by moisture, such as fiberglass and cellulose, should not be used to insulate a crawl space or basement. Interior basement insulation should be foam installed against the basement walls. It must be protected with fire-rated covering—drywall, spray-on coating, or fire-rated foam. If there is cellar hatchway to outdoors, be sure it is sealed and insulated. Installing an air barrier between the hatchway and the cellar, such as a door, may be a good option. Crawl Spaces The crawl space should be sealed, NOT ventilated. (Think of crawlspaces as small basements). Dirt Floors are a source of moisture and should be sealed: eliminate the source of any standing water then use 6-mil thick polyethylene sheeting as a vapor barrier to cover the ground and seal tightly to walls and columns. Then seal and insulate the walls, rim (band) joist and sill plate. Humidity Humidity is important for comfort. Humidity affects the rate skin is able to discharge heat. In the winter, higher humidity is more comfortable, because the water vapor on skin will not evaporate and will not take the heat from the body making one more comfortable at lower temperatures. In the summer, perspiration and evaporation cool the body. Humidity is water vapor in the atmosphere. The mass of water vapor per unit of air volume is called absolute humidity. Relative humidity is the ratio of the water vapor in the air compared to the amount of moisture the air could hold at that temperature. If the relative humidity is 100%, the air is saturated with water (it cannot hold any more water). If the relative humidity is 0 percent, then no water vapor is present. Clothes that are hung out to dry on humid days will dry more slowly than on dry days, because the air cannot absorb the water as quickly when it is mostly saturated. Air saturation depends on the amount of water in the air or the air temperature. The saturation point is called the dew point. When the air cools at night, the relative humidity will rise until the air is saturated. At that point, water will begin falling and this results in dew in the summer and frost in the winter. The temperature at which the amount of water in the air and the temperature intersect to have water condense is called the dew point. A number of household comfort and health problems stem from having either too much or too little humidity in the air. When the relative humidity indoors exceeds 50% on a continuing basis, usually in the summer, mold, mildew, and bacteria grow in furnishings, walls and ceilings. Windows and walls start to sweat and moisture condenses inside the walls and roof framing. This sets the stage for rot and allergies. If the air in a building is too dry, it can cause problems. Not only do occupants feel cold, but also when relative humidity is 15 percent or less, throat and nasal passages get too dry due to rapid evaporation. Furniture joints come apart, bookbindings crack, paint may not hold to some surfaces, plaster cracks, and static electricity becomes a nuisance. Both furnaces and boilers that are in the conditioned space that are not provided with outside combustion air will tend to lower the humidity of a house. Generally, people, animals and plants will increase humidity as the moisture in them evaporates. Similarly, boiling water, showers, and the dishwasher will also add water to the air. However, as the boilers and furnaces call for air for combustion, fresh cold and generally dry outside air will be brought into the house through air leaks. As this air is brought up to room temperature, it will seem even drier as the relative humidity falls. Furnaces often make the problem even worse due to their use of circulating air to heat the home. Most rooms have supply registers, but only a few also have return registers. If the


NORA Advanced Efficiency
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