HVAC 101


What's the most common mistake people make in trying to save energy around the house?
Common mistakes people make include:
- letting the furnace or air conditioner salesperson sell them a unit that's much bigger than they need,
- not getting the ducts checked for leakage when installing a new heating and cooling system,
- thinking that "since heat rises, we only need to insulate the attic." Floors over a basement or crawlspace, walls and windows also matter.
- not using ceiling and portable fans to improve comfort in the cooling season. They use very little electricity. Use them to circulate air in the house, tomake the house feel cooler by doing this, the thermostat setting for your air conditioner can be raised to 85?F, and still maintain the same comfort as the lower setting. 
What's the single biggest user of electricity in my house?
If your house has central air conditioning, the air conditioner will probably be the biggest user by far. Although used only a few months of the year, the annual cost can be much greater than the annual cost of your refrigerator, which is typically the next largest user. In hot climates, the annual air conditioner cost can exceed a thousand dollars. You can get a very rough idea of what your air conditioner is costing you by subtracting the electric portion of your bill in a spring month when you aren't using your air conditioner from the electric portion of the bill in the summer when you do use it. This gives you the monthly cost. Multiply this by the number of months you use your air conditioner to arrive at your approximate annual cost.  
We have an older house. Which should we do first?
Insulate or replace the furnace? Whether you should insulate or replace your furnace first depends on the situation in your house. Factors that influence this decision are the age and efficiency of your furnace, and the amount of insulation currently present in the house. In general it is more cost-effective to upgrade insulation than it is to upgrade your furnace. However, if your furnace is old, and you are planning on replacing it anyway, you might want to upgrade the furnace if you have to choose between the two options. The average lifetime for a furnace is between 15 and 20 years. The efficiency of furnaces has increased over the years, so the older a furnace is, the more likely that furnace is to be inefficient. The average efficiency of new furnaces has increased from 63% in 1972 to 83% in 1995. Older furnaces, and furnaces which are used a lot are more cost-effective to replace than newer or infrequently used furnaces. Also, if you insulate your house at the time of furnace replacement, you might be able to buy a smaller capacity furnace and save money on the price. The same holds true for A/C and other heating and cooling equipment. 
Air-sealing ducts
Measurements of heat pump performance indicate that duct leakage wastes 10 to 30 percent of the heating and/or cooling energy in a typical home. It's one of the most severe energy problems commonly found in homes because the leaking air is 20? to 70?F warmer than indoor air in winter and 15? to 30?F cooler in the summer. Duct leakage may cause some minor comfort problems when ducts are located in conditioned areas. But when leaky ducts are located in an attic or crawl space, the energy loss is often large. Some of the worst duct leakage occurs at joints between the air handler, and the main supply and return air ducts. Some main return ducts use plywood or fiberglass duct-board boxes. These boxes frequently leak because their joints are exposed to the duct system's highest air pressures. Heating and air-conditioning contractors often use wall, floor, and ceiling cavities as return ducts. These building-cavity return ducts are often accidentally connected to an attic, crawl space, or even the outdoors, creating serious air leakage. Fiberglass ducts and flex ducts are often installed improperly. These ducts may also deteriorate with age, leading to significant supply-duct leakage. The best heating and cooling contractors have equipment to test for duct leakage. Testing helps locate duct leaks and indicates how much duct sealing is necessary. Do not use duct tape for sealing?its life span is very short, often less than 6 months. 

What Causes Indoor Air Problems?
Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants. Pollutant Sources There are many sources of indoor air pollution in any home. These include combustion sources such as oil, gas, kerosene, coal, wood, and tobacco products; building materials and furnishings as diverse as deteriorated, asbestos-containing insulation, wet or damp carpet, and cabinetry or furniture made of certain pressed wood products; products for household cleaning and maintenance, personal care, or hobbies; central heating and cooling systems and humidification devices; and outdoor sources such as radon, pesticides, and outdoor air pollution. The relative importance of any single source depends on how much of a given pollutant it emits and how hazardous those emissions are. In some cases, factors such as how old the source is and whether it is properly maintained are significant. For example, an improperly adjusted gas stove can emit significantly more carbon monoxide than one that is properly adjusted. Some sources, such as building materials, furnishings, and household products like air fresheners, release pollutants more or less continuously. Other sources, related to activities carried out in the home, release pollutants intermittently. These include smoking, the use of unvented or malfunctioning stoves, furnaces, or space heaters, the use of solvents in cleaning and hobby activities, the use of paint strippers in redecorating activities, and the use of cleaning products and pesticides in housekeeping. High pollutant concentrations can remain in the air for long periods after some of these activities. Amount of Ventilation If too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Unless they are built with special mechanical means of ventilation, homes that are designed and constructed to minimize the amount of outdoor air that can "leak" into and out of the home may have higher pollutant levels than other homes. However, because some weather conditions can drastically reduce the amount of outdoor air that enters a home, pollutants can build up even in homes that are normally considered "leaky." http://www.epa.gov/iaq/pubs/insidest.html Indoor Air and Your Health Health effects from indoor air pollutants may be experienced soon after exposure or, possibly, years later. Immediate effects may show up after a single exposure or repeated exposures. These include irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue. Such immediate effects are usually short-term and treatable. Sometimes the treatment is simply eliminating the person's exposure to the source of the pollution, if it can be identified. Symptoms of some diseases, including asthma, hypersensitivity pneumonitis, and humidifier fever, may also show up soon after exposure to some indoor air pollutants. The likelihood of immediate reactions to indoor air pollutants depends on several factors. Age and preexisting medical conditions are two important influences. In other cases, whether a person reacts to a pollutant depends on individual sensitivity, which varies tremendously from person to person. Some people can become sensitized to biological pollutants after repeated exposures, and it appears that some people can become sensitized to chemical pollutants as well. Certain immediate effects are similar to those from colds or other viral diseases, so it is often difficult to determine if the symptoms are a result of exposure to indoor air pollution. For this reason, it is important to pay attention to the time and place the symptoms occur. If the symptoms fade or go away when a person is away from the home and return when the person returns, an effort should be made to identify indoor air sources that may be possible causes. Some effects may be made worse by an inadequate supply of outdoor air or from the heating, cooling, or humidity conditions prevalent in the home. Other health effects may show up either years after exposure has occurred or only after long or repeated periods of exposure. These effects, which include some respiratory diseases, heart disease, and cancer, can be severely debilitating or fatal. It is prudent to try to improve the indoor air quality in your home even if symptoms are not noticeable. While pollutants commonly found in indoor air are responsible for many harmful effects, there is considerable uncertainty about what concentrations or periods of exposure are necessary to produce specific health problems. People also react very differently to exposure to indoor air pollutants. Further research is needed to better understand which health effects occur after exposure to the average pollutant concentrations found in homes and which occur from the higher concentrations that occur for short periods of time.

Ask an Energy Expert Energy Efficiency and Renewable Energy Clearinghouse (EREC) P.O. Box 3048 Merrifield, VA 22116 (800) 363-3732 Fax: (703) 893-0400. 

Consumer Energy Information Web Site Energy experts at EREC provide free general and technical information to the public on many topics and technologies pertaining to energy efficiency and renewable energy. 

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This document was produced for the U.S. Department of Energy (DOE) by the National Renewable Energy Laboratory (NREL), a DOE national laboratory. DOE/GO-10097-375 FS 215 March 1997

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