Where do I buy a central air-conditioner, and what will it cost?

Answer:

You buy the complete system and servicing from an air-conditioning or heating contractor like Bush.

Although prices vary from region to region, you should expect to pay at least $3,000 to $8,000 for a package that includes installation and hardware. The larger the house, the higher the cost. Installation is cheapest and simplest if the air-conditioner can be tied into existing heating duct, even if their vents aren't optimally positioned to direct cool air into the rooms. But if the contractor has to install ducts, the price will climb. The number of ducts, their size and shape, and the amount of carpentry needed to hide them in walls and ceiling will vary from house to house.

What factors should I look for in a central air-conditioner?

Answer:
Two factors that matter the most are energy efficiency and cooling capacity. Of the two, efficiency is easier for you to determine. Manufacturers test their central air-conditioners according to Government standards and give them a Seasonal Energy Efficiency Rating (SEER), which lets you compare competing brands for efficiency over an entire cooling season. For systems of the same capacity, the higher the SEER the lower the operating cost. This means an 12 SEER unit uses less electricity than a 10 SEER. 

Government standards require any new central system whose compressor is separate from its evaporator to have a SEER of at least 10. The most efficient new models are rated at 18 or more, but some older model still on the market may have a SEER of less than 10. 

Cooling capacity is typically measured in "tons" of cooling, where one ton equals 12,000 Btu per hour. Other things being equal, the larger the capacity, the more the equipment costs and the more expensive it will be to run. A unit with too much cooling capacity for the house will cycle on and off more frequently than a properly sized one, and it may not dehumidify the rooms adequately. Researchers at Texas A&M University have found that slightly undersized units are more efficient and better at moisture removal than oversized systems. 

With even the most efficient air-conditioner, you can sharply reduce annual operating costs simply by raising the thermostat setting two or three degrees-from 74 to 76 say. That kind of small temperature change shouldn't cause you noticeable discomfort. 

What about dealing with humidity here in the South?

Answer:

You know how miserable humidity can make you. Well, with a variable speed air handler you can reduce the humidity in your home, giving you and your family a more comfortable environment. 

In fact, you'd probably be amazed to find out just how much moisture is in your home. Consider this a humidity control system. This alone could take out several more gallons of water a day.

How can I find out how much cooling capacity I need?

Answer:

Contractors use various rules of thumb, such as one ton of capacity for every 600 square feet in a well-insulated house or one ton for every 500 square feet in an under insulated house. 

Such rough guides don't always make allowances for important variables-the amount of sunlight striking a house, the area of exterior walls, the number of windows facing east and west (those windows admit the most intense heat in the summer), and so on. 

Formal sizing guides for contractors' use, such as one published by the Air-Conditioning Contractors of America as "Manual J' (Load Calculation for Residential Winter and Summer Air-Conditioning), allow for climate, house construction, and other factors. 

A good contractor should take the time to calculate cooling capacity with a guide like "Manual J" as part of the bid and to show you room-by-room requirements for cooling load and airflow. 

If new air ducts have to be installed, how can I be sure the work is done right?

Answer:

A good contractor will use a recognized set of duct-installation guidelines, such as the Air-Conditioner Contractors' "Manual D." Ducts need to be designed to deliver the proper amount of cool ;air to each room and to return a comparable amount of air to the evaporator coil. If the system can't maintain that balance, rooms won't cool properly and the air-conditioner may not achieve its maximum efficiency. In extreme cases, the evaporator coil may ice up, causing the cooling to stop and prompting a service call. The material used for the ducts also matters.

Flex duct, rather like an insulated version of the hose used for a clothes-dryer exhaust, is the cheapest and easiest to install but also the most prone to bending kinking, tearing, or leaking around joints. 

Duct board, a rigid fiberglass board with an outer barrier is cut and joined with special tools and tape to make square or rectangular ducts. Duct board is less susceptible to bending or kinking, but any tears in the outer barrier or improperly taped seams can allow cool air to escape. 

Galvanized steel duct usually a combination of prefabricated and custom-made parts for each installation, is generally the most expensive but also the strongest and most durable. It needs to be insulated where it passes through uncooled spaces-after all, you don't want to pay to air-condition the attic or an unfinished basement. 

No matter what material is used, the sections of duct should be firmly connected, not merely held together with duct tape. In order to maintain the proper airflow, ducts should turn corners smoothly, not sharply, and be adequately supported to prevent sagging. Cold air leaking from seams or migrating through the duct walls can drastically increase overall operating costs. 

Even the most watchful home-owner can't be sure the contractor has handled every part of the installation properly. Your best protection against faulty design or installation is monetary: Make the final payment to the contractor only after the system is installed and you're sure it runs properly.