With the arrival of hot weather, I have received many telephone calls and emails requesting information on central air conditioning systems. The very first thing that I tell everyone is that this is not a project for the average do-it-yourselfer because there are many specialized skill sets involved as well as specialized tools that are quite expensive to purchase. How much a central A/C system will cost depends on a number of factors. If you home is already equipped with central hot air heating system, central A/C will cost you somewhere between $3500 and $4000 and can be installed in two days by two highly trained technicians. These figures are based on a home with a 2000 FT2 living space. On the other hand, if your home isn’t heated by a central hot air system, the installers will have to install the ductwork. If the contractor needs to install new ductwork, the price for central air can quickly increase to $8000 or more for a 2000 FT2 home.
Heat Gain Calculations Selecting and installing the proper system for your home begins with the contractor performing a "J Load" calculation. This heat gain calculation is based on the instructions in the Air Conditioning Contractors of America manual J. This is a relatively simple audit for the trained professional to perform and reveals the size A/C unit required to cool your home efficiently. Where you live; the type and amount of insulation in your home; the number of windows and doors in your home; and your home’s orientation are all factor taken into consideration during the J-Load calculations. Most professionals use a software program like HVAC-Calc Residential 4.0, which sells for $400. If you want to conduct your own professional heat gain/heat loss audit, you can download a free trial copy of the Homeowners edition using this link http://www.sleeth.com/main.asp. If you like the way it works you can purchase it for your personal use for $49. Considering the fact that most professional charge $450 for the first 2000 FT2 and $50 more for each additional 1000 FT2 you could earn that back and more for doing energy audits for your friends and neighbors.
Based on the heat gain calculations the contractor will select a properly sized A//C unit. Air conditioners are rated in either Btu/h (British Thermal Units per Hour) or in tons. One ton is equal to 12,000 Btu/h. Properly sizing the unit is of primary importance because both an undersized unit and an over sized unit will waste energy. An undersized unit will not have the cooling capacity needed to cool your home efficiently and will run longer and harder than a properly sized unit. An oversized unit will have a larger compressor than necessary and thus consume more energy than a properly sized unit.
The next thing that a contractor should talk with you about is SEER Ratings. SEER stands for Seasonal Energy Efficiency Rating. The SEER number refers to how many Btu of heat the unit removes for each watt of electricity it consumes. The higher the SEER numbers, the less it will cost you to operate the unit. Under the new Federal Law, all new A/C units must have a minimum SEER number of 13. The higher the SEER number the more the unit will cost but the money you will save over the life of the unit will be many time that cost difference.
The package system is essentially a very large window unit with ductwork attached. The condenser, evaporator, compressor, and fans are all located in one package with ductwork running directly from that package. These units are very rare today. The split system splits the system into two packages. The condenser/compressor unit is located outside the home with the evaporator/fan unit located inside the home. The two units are connected together by copper tubing that carries the refrigerant back and forth between them. If your home is equipped with forced hot air heating the evaporator/fan unit is usually installed in the hot air furnaces plenum chamber. If there isn’t enough room in the plenum chamber a new plenum chamber will be fashioned from sheet metal and the fan/evaporator unit installed in that. If your home isn’t heated by a forced hot air system, the evaporator/fan unit is usually placed in the attic or attic crawl space to make running the new metal ductwork easier and less conspicuous. In closing, I want to say again that this isn’t a project for the do-it-yourselfer. Properly sizing the A/C unit, placing the condenser/compressor unit and the evaporator/fan unit in the optimal locations, properly sizing and installing the ductwork with minimal disruptions to the residents structural integrity all takes years of training and experience. That’s what you are really paying for when you hire a professional and in this case, it’s well worth the cost.
