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There are several issues you should consider when adding central air conditioning to an existing heating system.
"If a home has an older heating system with no provisions for central air conditioning, the duct work may be smaller than what is required for air conditioning," said Gene Meyer, extension mechanical engineer at Kansas State University.
As a result, your will have to increase the fan speed to compensate for the duct work. A larger motor often is required to achieve this higher flow rate.
"In extreme cases, it may be necessary to replace the supply duct work," Meyer said.
The location of the return-air registers also plays a role in comfort. In older homes, there were often no return-air registers installed on the second floor of a two-story home. It is difficult to cool the second story if this is the case. It may be necessary to install return-air duct work.
Another consideration is the requirement for a floor drain below the furnace level. Air conditioners produce condensate when they operate. This condensate is the consequence of removing moisture from the air.
"If a floor drain is not available below the level of the furnace, you can purchase a small condensate pump set," Meyer said. "For approximately $60, this set will pump the condensate to a convenient disposal site."
A final consideration is the arrangement of the duct work at the furnace outlet.
"The duct work around the furnace must leave sufficient room for the installation of the cooling coil," Meyer said.
When installing central air, it is an excellent time to check the supply and return air ducts for leaks. Inadequate air flow across the cooling coil is the No. 1 cause for poor air-conditioning system performance.
"First, run another test to confirm the results of your initial test," said Bruce Snead, extension specialist in residential energy at Kansas State University. "If your first test showed an elevated level of radon, say 10 pCi/L or greater, a second charcoal canister test will provide a quick confirmation."
If the first test result was closer to 4 pCi/L, conduct either another short-term, or a long-term test of three to 12 months in duration. The long-term method gives a more average indication of the radon levels in the space. Either approach to testing is acceptable and can provide an accurate basis for deciding whether or not to fix your house.
"The key to getting a valid test and accurate results is to follow the directions on the test kit and use a device that has ‘Listed by EPA’ on its packaging," said Snead.
You should test in the lowest lived-in level of your house, usually the basement, and in the room where you spend the most time. It is also wise to test in more that one location if there are different foundation types in your home, such as a basement and crawlspace or adjacent slab-on-grade areas used as living areas.
"If the radon level is confirmed as elevated through appropriate testing, you will want to take actions to reduce the radon level within the next year," Snead said.
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"There appears to be little correlation between the air-tightness of a house and the potential for radon contamination," said Bruce Snead extension specialist in residential energy at Kansas State University.
Some older homes, which generally are leakier than newer ones, have the characteristics that make them prime candidates for elevated radon levels.
Radon is a radioactive gas produced by the decay of uranium 238, which is found in the soil.
"As a gas, it can be drawn into a basement from the surrounding soil through various cracks and openings," Snead said.
Some of the characteristics to look for include open soil in the basement or in a crawl space that opens into the basement, basement floors with large cracks, open sumps or drains, and large furnaces or boilers creating a negative air pressure in the basement.
"Negative air pressure can increase the rate at which the radon enters through these cracks and openings," Snead said. "Of course, some of these same openings can be found in a new basement."
The only assured way to determine if a radon problem exists is to have your house tested.
"A relatively inexpensive and widely available method of detecting radon contamination in your home is to purchase charcoal pouch-type test kits from a local extension office or health department," Snead said. "You can also order these tests by mail from several companies and may be able to purchase them from local retail stores."
You can obtain the list of the companies offering radon testing products and services by calling the Kansas Department of Health and Environment at 800-693-5343.
You can check a few items that should indicate if your air conditioner has problems.
First, check the two lines connected to the outside of the air conditioner," said Gene Meyer, extension mechanical engineer at Kansas State University. "The larger one—the suction line—should be cool to the touch. It should not be so cold, however, that frost develops."
The smaller line—the high pressure line—should be warm, but not hot. It should be 20 to 30 degrees warmer than the outside temperature.
"In extreme cases, it will be hot to the touch, so be cautious," Meyer said. "If this is the case, call a service technician."
Some air conditioners are equipped with a sight glass in the high pressure line (the small line). The glass should be clear, with no bubbles visible while the system is running. Cloudy liquid in the sight glass may indicate contamination of the system.
"One final check you can make is to measure the temperature of the air as it leaves the register," Meyer said. "It should be 15-20 degrees cooler than the room temperature."
If the building is warm, humid or if the duct work is not insulated, then you may get smaller temperature differences.
"These guides are not intended to eliminate the need for an annual check by a qualified service person," Meyer said. "If you suspect problems, call for help from someone familiar with air conditioners."
The effectiveness of a sun-control device is determined by four factors: its shape and form, its location near the window, its color and the reflectivity of the materials used.
"If possible, an exterior shading device should be your choice, because it stops the sun's heat outside your home," said Bruce Snead, extension specialist in residential energy at Kansas State University. "Natural vegetation is the ideal choice."
Trees and shrubs can be located to provide complete shading during the appropriate time of year. Adjustable horizontal or vertical louvers, mounted outside the window, also can provide complete shading if operated properly.
"They are more costly, however, than most other options," Snead said.
Awnings are a widely-used exterior shading option, because they provide good shade and permit full ventilation.
"Awnings should be opaque and vented at the top to prevent heat buildup underneath," Snead said.
Reflective solar screens can stop 50 to 60 percent of the solar gain without stopping ventilation.
"They have the advantage of being removable to allow full penetration of the winter sun into your home," Snead said.
Interior shading devices include window films and aluminum foil attached to the inside of a window.
"These are inexpensive, though less effective options," Snead said.
Roller shades and drapes also reduce incoming solar energy and are most effective if they are white or light-colored.
"Dark-colored drapes or shades, and Venetian blinds are the least effective shading options," Snead said.
"The T designation refers to the diameter of the lamp in eighths of an inch," said Gene Meyer, extension mechanical engineer at Kansas State University.
For example, a T-12 lamp is 12 times 1/8-inch or 1 1/2 inches in diameter.
"For years, most 4-foot fluorescent lamps were T-12 lamps," Meyer said. "Recently, energy efficient T-8 lamps have become popular. Not only are the lamps smaller in diameter, they use special phosphors that emit more light."
T-8 lamps usually require special ballasts to operate properly.
"A number of conditions can cause paint to blister and peel," said Richard B. Hayter, director of Engineering Extension at Kansas State University. They include poor surface preparation, poor quality paint, painting on hot days in direct sunlight, and the introduction and presence of moisture in the wood being painted.
"Although the moisture problem is common, it is the least obvious," Hayter said. "The moisture may have accumulated from the water vapor inside the home during the winter, or may be introduced through exterior leakage."
This problem is prevalent in older homes that have no vapor barrier on the inside of the wall. In the winter, the humidity ratio is typically higher inside the house than outside, particularly if the home is equipped with a humidifier.
"If a vapor barrier is not present on the interior side of the wall, vapor will penetrate, eventually condense and possibly freeze inside the wall cavity or insulation," Hayter said.
As the wall warms during the spring, the condensation vaporizes and migrates to the exterior wall. As this vapor reaches the painted surface, it can create a paint blister.
"These blisters may rupture eventually, and cause the paint to peel," Hayter said.
Three remedies for reducing paint blisters caused by moisture in walls exist.
"Be sure humidity levels are not excessive in your home in the winter—typically not more than 30 percent," Hayter said. "Second, some form of vapor barrier should be installed to prevent water vapor from penetrating the walls. Third, check building materials and joints where peeling occurs for water entry points and seal them with caulk or paint."
Ideally, a continuous film is installed directly behind the interior wall surface. In existing homes, vapor migration can be reduced by using vapor-retarding paint or wallpaper.
One cause of excess humidity during the winter is the moisture that penetrates foundation walls.
"If the roof of your home is not equipped with gutters, and the grading around the foundation permits water to flow toward the foundation, moisture may seep through the basement walls and cause excessive humidity," Hayter said.
"High head pressure can result from several problems in a refrigeration system," said Gene Meyer, extension mechanical engineer at Kansas State University. "One common problem is that the condenser cannot dissipate enough heat."
If the codenser is undersized or cannot dissipate enough heat due to air circulation, the temperature and pressure in the condenser rise, and the compressor works harder. In time, this increased work causes the compressor to fail.
"One common cause of high head is a dirty or plugged condenser," Meyer said. "The solution is to clean the condenser."
Another cause can be lack of adequate air flow into the condenser. Often, shrubs or other barriers are erected to hide the condensing unit from view. These can obstruct the air flow and reduce the heat rejection rate.
"Sometimes the condenser is not sized correctly," Meyer said.
One permanent solution is to replace the condenser with a larger one. Another solution is to add an evaporative cooler to lower the air temperature prior to admitting it to the condenser.
These will reduce energy usage and lengthen compressor life.
"If high head pressure occurs only on very hot days, a simple solution is spraying water on the condenser," Meyer said.
"I don't recommend this for an extended period, however, because minerals from the water will collect on the condenser and increase the problem next year."
An attic fan ventilates only the attic by drawing in air through the attic vents. It is installed in the roof or gable. It turns on whenever the attic temperature reaches a high temperature.
"Research shows that any savings in air conditioning costs because of an attic fan generally are offset by the cost to operate the fan," said Doug Walter, president of Kansas Building Science Institute, Manhattan.
A whole-house fan ventilates the house and uses the attic vents only for discharging the air. The fan is located in the ceiling between the occupied space and the attic.
"It cools the house by pulling in cool outside air through open windows," Walter said.
A whole-house fan can save a significant amount of energy by reducing the need for air conditioning when outside temperatures and relative humidities are in the comfort range.