In addition to using less energy to operate, energy-efficient heating and cooling systems can be quieter, reduce indoor humidity, and improve the overall comfort of the home. When properly installed into a tightly sealed home, this equipment won't have to work so hard to heat and cool the home.
As much as half of the energy used in your home goes to heating and cooling. So making smart decisions about your home's heating, ventilating, and air conditioning (HVAC) system can have a big effect on your utility bills — and your comfort.
A wide variety of technologies are available for heating and cooling your home, and they achieve a wide range of efficiencies in converting their energy sources into useful heat or cool air for your home. In addition, many heating and cooling systems have certain supporting equipment in common, such as thermostats and ducts, which provide opportunities for saving energy. Key components of an efficient HVAC system include:
Mechanical equipment, ductwork and plumbing should not be located in exterior walls, vented attics or vented crawlspaces if possible. All air distribution systems should be located within the conditioned space. Interior chases must be considered and provided during the schematic design phase to make it easy to install services. A designer must think about stair locations and openings while allowing ductwork and plumbing to get by them as it goes from one side of the house to the other and from one floor to another.
Seal and insulate ducts in attics and crawlspaces.
Ducts that move air to-and-from a forced air furnace, central air conditioner, or heat pump are often big energy wasters. Sealing and insulating ducts can improve the efficiency of your heating and cooling system by as much as 20 percent — and sometimes much more. It is of primary importance to seal ducts that run through the attic, crawlspace, unheated basement, or garage. Use duct sealant (mastic) or metal-backed (foil) tape to seal the seams and connections of ducts. After sealing the ducts in those spaces, wrap the ducts in insulation to keep them from getting hot in the summer or cold in the winter.
Install high-efficiency heating and cooling equipment.
Well-designed high-efficiency furnaces, boilers, and air conditioners (and distribution systems) not only save building occupants money, but also produce less pollution. Install equipment with minimal risk of combustion gas spillage, such as sealed-combustion appliances.
Central Air Conditioners: ENERGY STAR qualified central air conditioners have a higher seasonal efficiency rating (SEER) than standard models, which makes them about 14% more efficient than standard models.
Geothermal Heat Pumps: Geothermal heat pumps are similar to ordinary heat pumps, but use the ground instead of outside air to provide heating, air conditioning and, in most cases, hot water. Because they use the earth's natural heat, they are among the most efficient and comfortable heating and cooling technologies currently available. ENERGY STAR qualified geothermal heat pumps use about 30% less energy than a standard heat pump. They are quieter than conventional systems.
Furnaces: Furnaces are the most common residential heating system in the U.S. ENERGY STAR qualified oil and gas furnaces have annual fuel utilization efficiency (AFUE) ratings of 83% and 90%, or higher, making them up to 15% more efficient than standard models. Furnaces heat air and distribute the heated air through the house using ducts.
Understanding the Efficiency Rating of Furnaces and Boilers:
A central furnace’s efficiency is measured by annual fuel utilization efficiency (AFUE) and is a measure of how efficient the appliance is in the energy in its fuel over the course of a typical year.
Specifically, AFUE is the ratio of heat output of the furnace or boiler compared to the total energy consumed by a furnace or boiler. An AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere. AFUE doesn't include the heat losses of the duct system or piping, which can be as much as 35% of the energy for output of the furnace when ducts are located in the attic.
An all-electric furnace has no flue loss through a chimney. The AFUE rating for an all-electric furnace or boiler is between 95% and 100%. The lower values are for units installed outdoors because they have greater jacket heat loss. However, despite their high efficiency, the higher cost of electricity in most parts of the country makes all-electric furnaces or boilers an uneconomic choice. If you are interested in electric heating, consider installing a heat pump system.
High-efficiency heating systems will often condense flue gases in a second heat exchanger for extra efficiency, have sealed combustion, and a 90%–97% AFUE rating.
Calculate the size of equipment.
Heating and cooling systems should be custom fit for your home. Sizing and a handful of other installation practices can dramatically affect how well your new equipment will deliver comfort and savings. Proper equipment sizing is based your home's heat loss during cold weather and heat gains during warm weather. The calculation is usually done using software, and should be based on professional guidelines such as Manual J from the Air Conditioning Contractors of America (ACCA) or similar method. Oversized equipment can cause reduced comfort and excessive "air" noise. Oversizing will shorten the life of the equipment by causing it to cycle on and off more frequently than a properly-sized unit. Undersized equipment, with airflow that is too low, can reduce the efficiency of the air distribution and accelerate wear on system components, leading to earlier failure. After the design load calculation is completed, ducts, supply registers, and return grilles can be sized and selected using professional guidelines in ACCA's Manual D or similar method.
Thermostats and Control Systems.
You can easily save energy in the winter by setting the thermostat to 68°F while you're awake and setting it lower while you're asleep or away from home. By turning your thermostat back 10°–15° for 8 hours, you can save about 5%–15% a year on your heating bill—a savings of as much as 1% for each degree if the setback period is eight hours long. The percentage of savings from setback is greater for buildings in milder climates than for those in more severe climates.
In the summer, you can follow the same strategy with central air conditioning, too, by keeping your house warmer than normal when you are away, and lowering the thermostat setting to 78°F (26°C) only when you are at home and need cooling. Although thermostats can be adjusted manually, programmable thermostats will avoid any discomfort by returning temperatures to normal as you wake or return home.
A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save.
The best designed and installed high-efficiency HVAC system can quickly loose its efficiency, effectiveness and lifespan without periodic maintenance per the manufacturer's specifications.
Change your air filter regularly. Check your filter every month, especially during heavy use months (winter and summer). If the filter looks dirty after a month, change it. At a minimum, change the filter every 3 months. A dirty filter will slow down air flow and make the system work harder to keep you warm or cool — wasting energy. A clean filter will also prevent dust and dirt from building up in the system — leading to expensive maintenance and/or early system failure.
Tune up your HVAC equipment yearly. Just as a tune-up for your car can improve your gas mileage, a yearly tune-up of your heating and cooling system can improve efficiency and comfort.