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Window air conditioners are certainly better than no air conditioners at all on a hot summer day, but quieter, more efficient central air conditioning represents a major step up in household comfort. Often referred to as just central air, a whole-house central air conditioning system distributes cooled air through a home or office space via a duct system. Central air can be added to your existing forced-air heating system, although an existing HVAC network isn't required. In this buying guide you'll learn more about centralized air conditioning and the cost.
How Does an Air Conditioner Work?
An HVAC includes a thermostat that registers temperature, ductwork to draw and expel air, the air handling unit, an evaporator coil filled with refrigerant, a compressor, and a blower. The basic cycle includes:
- The thermostat registers temperatures above the level you set and sends a signal to the air handling unit
- The air handler draws in air through the ductwork
- The air passes over the evaporator coil
- The refrigerant within the coil cools the air
- The unit sends the cooled air back through the ductwork
- The blower sends the air through the vents into the home
- The evaporator coil sends the refrigerant back through the compressor to be re-cooled so it's ready for the next cycle
Central Air Conditioning Considerations
Below are some of the points you should keep in mind when shopping for a new central air conditioner.
Types of Cooling Systems
There is more than one type of cooling system. The ideal type depends on your home but also the climate where you live. Some houses may be suitable for multiple options, but some may not have the proper setup required by different cooling systems.
Central Air Options
- Standard central air: To truly be a central air system, there must be ducts in place to distribute cooled air throughout the come. The most common type of system is referred to as a split system, wherein the refrigerant circulates between an indoor evaporator coil and an outdoor compressor and condenser. Standard central air systems follow the model of operation described above.
- Packaged units: Unlike a split system central air conditioner, packaged units have a single piece of equipment that houses the compressor, condenser, and evaporator. They work similarly to split system units, with the exception that the refrigerant does not have to travel to a secondary unit. Packaged units also often contain a furnace.
- Split ductless systems: While not technically a central air system, split ductless systems provide cooling effects similar to central air. These systems feature an outdoor compressor and condenser and multiple air handlers. There is a conduit that connects the indoor and outdoor sections, which also houses a condensate drain, the power cable, and refrigerant tubing. The system is controlled via a remote and each air handler cools the room it is installed in.
Additional Cooling Options
- Room air conditioners: These are designed specifically to cool an individual room. Typically mounted in windows or other wall openings, they are cheaper than central air systems but do not offer the same cooling power; multiple units would be needed to match a central air system.
- Evaporative coolers: Also known as swamp coolers, these cooling systems are more common in dryer areas. They pull in outside air through moist pads which cool the air, releasing it back into the home. It may not seem very effective, but evaporative coolers can create inside air that's 30 degrees lower than the temperature outside.
Factors to Consider When Choosing a Central Air Unit
Multiple factors determine the type of air conditioning unit you should get. First, you consider the energy efficiency and seasonal energy efficiency ratio (SEER) rating of the unit. If you are replacing an old unit, newer units with higher SEER rating are considerably more affordable than they used to be. Remember, the higher the SEER value and the better the energy efficiency, the higher the savings.
Also, have a professional provide estimates as to proper unit size. An under- or oversized unit renders the process of installing or replacing air conditioning essentially useless. A heat load calculation is the only surefire way to get the the right size AC unit.
Once you've decided on the type of central air conditioning system, it's crucial to select a setup that is powerful enough to cool your entire home on hot days, but not so powerful that it doesn't adequately remove humidity. The size of an air conditioner is expressed in tonnage or BTUs (British Thermal Units) per hour. A cooling contractor can help you evaluate the size of the system you need by performing what's known as a Manual J load calculation.
When it Comes to Your Air Conditioner, Size Matters
It is absolutely crucial that your AC unit is the appropriate size for your home. To ensure you get the right size, contact a professional for a consultation so that all the pertinent aspects of your home are taken into account. A professional considers factors such as the age of the home, square footage and volume of a home's living space, the number and condition of windows, and the existing ductwork and vents.
Both oversized and undersized systems should be avoided. Oversized systems cool the air in your home rapidly, leading the system to shut off before it should. Though the air in the home has been cooled, the building structure itself is not, allowing heat and humidity to seep in and start the system again. This causes the system to run multiple time for too short of a time and the cost quickly adds up. Undersized systems simply do not cool your home properly, causing the system to run constantly which also increases the cost. In both instances, your AC fails sooner and your utility bills are higher than if you'd bought the correct size unit from the beginning.
Understanding AC Sizing Terms
The size of an air conditioner is rated in tons of cooling capacity, with one ton of cooling being equal to 12,000 British thermal units (BTUs) per hour. A standard residential air conditioner is a 2-ton unit, equating to 24,000 BTU per hour. It is important to note, however, that just because two units have the same tonnage it does not mean that they are the same.
Energy efficiency and Seasonal Energy Efficiency Ratios (SEERs) vary from unit to unit. Once you figure out the correct tonnage for your home, consider SEER ratings as you look at different units. Higher SEER rating use less energy, with each SEER using approximately 5 percent less (i.e a 15 SEER unit is roughly 15 percent more efficient than a 12 SEER unit). Central air is one of the most expensive aspects of any home, but installing a unit that's properly sized and has a decent SEER rating significantly reduces those costs.
How to Determine the Correct Size
A truly accurate estimate of the necessary AC unit size for your home requires a professional load calculation, referred to as the Manual J. The majority of installers include this free of charge as a part of their estimate. There are two types of Manual J calculation: room-by-room and whole house.
Room-by-room calculation determines the amount of cooling needed per room, with all results being added together in the end. This is the more accurate method of calculation and is recommended if you are replacing your existing ductwork. Whole house calculation determines the amount of cooling required by the home as a whole. This method is recommended if you are not planning on modifying or replacing your existing ductwork.
It is best to get an estimate from a professional, but that does not mean you can't get a rough estimate of your own.
The equation is: [(house sq. ft. x 25) / 12,000) - 0.5] = required tonnage for your home.
Please note: If you live in an area where temperatures are higher most of the year, you need to add 0.5 instead of subtract it.
While this equation gives you an idea of what unit size you need, it is always more accurate) to consult a professional.
Although sizing for central air conditionings systems is determined formulaically, there is more leeway when choosing system efficiency. The seasonal energy efficiency rating (SEER) of an air conditioner expresses how much cooling unit provides relative to the amount of energy it uses. The higher a unit's SEER rating, the more efficient, and less costly, it is to run. The federal SEER minimum is 13, while 16 to 23 SEER is considered high efficiency.
Central Air Average Costs
The actual cost of central air installation depends on a number of factors, including the size of the home as well as the unit's tonnage and SEER rating.
- In a 2,000 square foot home with existing ductwork, central air conditioning costs $4,000 to $6,000 installed. If ductwork is additionally required, costs could reach $8,000 to $12,000 or more.
- Mini Split ductless units: A single ductless unit has an average cost of $1,800, but keep in mind that is for a single air handler. An 1,800 square foot home typically requires a system with at least four blowers, which costs around $3,800.
- Split ductless Installation averages between $10 and $40 per hour, with additional service fees starting around $50.
- Note that while a high efficiency unit could cost up to 30 to 40 percent more than one with the minimum 13 SEER rating, the extra costs should be recouped in energy savings over the lifetime of the system.
- Room air conditioners: A window-mounted room air conditioner designed to cool a room between 150 and 400 square feet typically costs between $100 and $300. Units to cool a larger space may cost between $300 and $800.
- Evaporative cooler: Portable swamp coolers have an average cost of $400, with units for the entire home coming in around $2,000. Including installation and service fees, the average cost of installing an evaporative cooler in a 1,500 square foot home is $3,900.