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Some Advice and Tips to Consider When Buying a New System

Central Air Conditioner Buying Tips

The type and size of air conditioner you need depends on your climate and cooling loads. Evaporative coolers are practical in hot, arid regions such as the southwest. For other regions, compressor-driven air-conditioning systems are the only choice.
When you are shopping for a central air conditioner, look for a SEER rating higher than 12.00 SEER.
If you already have a forced-air heating system, you may be able to tie an air conditioner into existing ducts, depending on their size and your home's relative heating and cooling loads. A good HVAC contractor can do the calculations for you.
Proper sizing and installation are key elements in determining air conditioner efficiency. Too large a unit will not adequately remove humidity. Too small unit will not be able to maintain a comfortable temperature on the hottest days. Improper unit location, lack of duct insulation, improper duct sealing, and incorrect refrigerant charge can greatly diminish efficiency
When buying a central air conditioner, look for a system with a fan-only switch so you can use the unit for nighttime ventilation to substantially reduce air-conditioning costs; a filter check light to remind you to check the filter after a predetermined number of operating hours; and an automatic-delay fan switch to turn off the fan a few minutes after the compressor turns off.
Look for a unit with quiet operation.
If you need or want to replace your existing air conditioner's outdoor (compressor) unit, make sure the indoor (blower coil) unit is compatible with the new outdoor unit. A highly efficient outdoor unit will not achieve its rated efficiency if paired with an older blower coil.

Tips for Buying a New Room Air Conditioner

When shopping for an air conditioner, first determine which type of system best suits your needs- central air conditioning or room air conditioning. Central air conditioners are designed to cool an entire house, while room air conditioners are usually window-or wall-mounted units that only cool the immediate area.
Three types of room air conditioners are available: (1) window models that can be installed in most double-hung windows; (2) ductless mini-split systems (3) (PTAC) built-in models that are encased in a sleeve installed in the wall.
Proper sizing is very important for efficient air conditioning. A bigger unit is not necessarily better because a unit that is too large will not cool an area uniformly. A small unit running for an extended period operates more efficiently and is more effective at dehumidifying than a large unit that cycles on and off too frequently.
When determining the appropriate size air conditioner for your home, consider the dimensions of the area to be cooled. Based on size alone, an air conditioner generally needs 20 Btu for each square foot of living space. Another popular formula is based on 400-500 square feet per ton. Other important factors to consider when selecting an air conditioner are room height, local climate, shading, window size, etc.
Verify that your home's electrical system can meet the unit's power requirements. Room units operate on 115-volt or 230-volt circuits. The standard household receptacle is a connection for a 115-volt branch circuit. Large room units rated at 115 volts may require a dedicated circuit and room units rated at 230 volts may require a special circuit.
If you are mounting your air conditioner near the corner of a room, look for a unit with an airflow in the desired direction for your room layout.
Look for a unit whose filter slides out easily for regular cleaning.
Select a unit with logically arranged controls, a digital readout for the thermostat setting, and a built-in timer.
When considering several comparable units, select the unit with the higher EER.