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Your House as a System

Your house is made up of various component parts that work together as a system. Heating and cooling your house affects air flow, air quality, and moisture migration. Chimney Effect

Heat Transfer
When you heat the air in your house, the air becomes lighter and more buoyant. It rises to the top of the living space. The air and heat are pushing on the ceiling. At the bottom of the living space there is decreased air pressure and temperature. Warm house air is pushed into the attic and cooler basement or crawl space air is being drawn in at the floor levels.

This is called the chimney effect or stack effect. The house is behaving like a fireplace chimney. Warm air leaks out the top, and cool air is drawn in at the bottom. Much of the heat you are paying for leaks into the attic. At the lower floor levels, your feet get cold. This phenomena occurs in all homes - it's just a question of to what degree. An AccuSpec Energy Efficiency Analysiswill help you determine how much air leakage your house has, where it occurs, and what to do about it. Heat MovingHeat moves constantly.

It moves in a variety of ways from warm areas to cooler areas.  It moves through solid materials (conduction). It moves through space (radiation). And it moves by being carried in the air (convection).

In the winter the heated air transfers into the attic through the ceiling materials by conduction. It also moves by convection through openings and bypasses such as plumbing and chimney chases, wiring runs, loose ductwork, leaky recessed ceiling lights, etc. In the summer the heat moves from the attic to the living spaces in the same manner.

Moisture Migration
Winter Moisture Migration In winter rising heated air carries moisture into the attic. The moisture is in the form of water vapor, which is put into the air by plants, appliances, cooking, bathing, breathing, etc. It is also sucked in (by the stack effect) from crawl spaces and basements. Air pollutants potentially are sucked in from these areas as well.

Attic ventilation is intended to evacuate the moisten laden air to the outside of the house. If the moisture is too intense and the ventilation is lacking, then in very cold times the moisture can condense out of the air when if contacts cold framing components. This can lead to mold, mildew, fungus growth, unhealthy air, and building material damage.

Older Homes
Older homes usually leak more air than newer homes. The chimney effect is hard at work. A lot of heat is escaping into the attic and other areas, and the cost of heating is high. The interior air is dryer because the warm moist air is being quickly replaced by dryer exterior air. There is one advantage to this however; The interior air is less prone to air quality problems.

Many homeowners will wisely add more insulation in the attic. This is likely to require that more ventilation be added as well. When insulation levels were low, the warm air in the attic kept the building components warm and condensation did not occur. But now, because some moisture will continue to enter the attic and because the framing components will be colder, more ventilation may be required.

Newer Homes
Newer homes are usually more air tight than older homes, and usually are more economical to heat and cool. As a result, newer homes are more susceptible to indoor air quality and moisture problems. Contaminants have a tendency to stick around a little longer.

An AccuSpec Energy Efficiency Analysis will help you determine how much air leakage your older or newer home has, where it occurs, and what to do about it.

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