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During the past several years, more and more "high performance" houses have been built, reducing the energy bills of tens of thousands of homeowners. As this new construction model continues to increase in popularity – for obvious reasons – it also carries risks that can be minimized by planning and installing effective insulation and duct work.
The intent of a high performance home is to completely seal the structure to keep outside air from the inside of the home. We do need some fresh air in the house, but the idea is to bring in the exact amount needed, filter it, and mix it with conditioned air. From a standpoint of energy efficiency, this is the best way to build a home today.
The area of the house that is sealed, however, should be on the underside of the roof decking, rather than the traditional method of laying insulation on the bottom of the attic. In this way, the air conditioning can be reduced, the R-value on the ductwork can be less, there will be less dust in the home, and no fiberglass particles floating around in the attic. Some people might think, "I never go in the attic. Why would I care what's up there?" Take a look around your ceiling and count the number of holes: duct supply grilles, can lights, bathroom exhaust fans, and any fixture with a wire coming out from the attic. None of these holes are sealed, leaving an opening as large as 1/4" around each hole.
Ever notice the dirt around the supply grilles in the ceiling? This dirt, along with fiberglass from insulation and other contaminants, that has entered the home through small holes in the ceiling is pulled into the living area of the house by "negative pressure." Any negative pressure in the home can occur when the dryer is on, a vent hood is on, or a bath fan is on. When these fans are running, they remove air from the home and exhaust it outside. This air must come from somewhere, so it pulls from any source possible, such as holes in the ceiling. The air in the attic is being pulled into the home causing dust to be deposited in the living area as it moves through the openings. Since holes in the ceiling are necessary, it makes the most sense to move the insulation to the next barrier, the underside of the roof deck. In that way, the attic is part of the "conditioned space," making it as much as 50 degrees cooler than it would otherwise have been.
By moving insulation to the roof decking, your heating and cooling equipment in the attic is no longer operating in a 130 degree environment while trying to cool your home, and any air leakage through duct loss is not costing you money through your utility bills. Proper air flow within the attic and living areas is also an important element of planning and constructing a high performance home.
The idea of a foamed, sealed attic is becoming more popular, but as more and more people are sealing the structure to protect themselves from high utility costs, the learning curve of properly installing gas appliances has lagged behind.
All gas-burning appliances require air to feed the flame that heats the air or water for which the appliance was designed. Ideally, these gas-burning appliances bring air to the appliance from outside the structure.
If a standard furnace is installed in a sealed home without proper duct work, the combustion air (the air that feeds the flame) will be pulled from the conditioned air, causing a negative pressure inside the house. This air will be replaced from any source available, including the vents of other gas-burning appliances, causing the vent gases to downdraft, possibly causing carbon monoxide gas to enter the living area.
This problem with gas-burning equipment such as furnaces, water heaters or "tankless" water heaters, can be eliminated by installing "sealed combustion appliances" that bring in air from outside the structure. Anyone building a sealed structure must make sure all the gas burning appliances are rated for sealed combustion.
This also includes wood-burning fireplaces, which must have an outside air source to feed the flames, or the air will come from inside the home. In a tight, high performance home, there will not be enough air leaking into the house to allow the fire to draw up the chimney, causing smoke to roll back into the home. If you are planning to build or purchase a high performance house, ensure that both the insulation and duct work is installed properly, allowing you to safely enjoy an energy efficient home. You can go to the new construction page of this web site to see a list of builders that are well qualified to build your new high performance home.
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