Do you have the necessary ductwork? If you're replacing an existing central air conditioner, then your house will already have a system of ducts in place. However, your contractor should still check out the ducts to make sure they are in good condition. Be sure to tell the contractor about any problems you are having with airflow or uneven cooling with your existing system, since this may be a sign of poorly designed ductwork. If you are adding a new air conditioner, you may be able to connect it to the ductwork for your central heating system, although it may need some modifications. If your home has no ductwork, you might want to consider a ductless mini-split system.
Consider your climate. If you live in a hot, humid climate, it's especially important to choose an air conditioner with a high SEER, since the air conditioner will be running a lot. In a hot, dry climate, EER is more important than SEER; it measures how effective the air conditioner will be in the hottest weather. People who live in dry climates might also consider skipping the air conditioner in favor of an evaporative cooler, or swamp cooler, which uses less energy. In mild climates, consider a heat pump, which could meet your needs for heating as well as cooling.
What rebates are available? As mentioned above, all Energy Star-rated central air conditioners can get you a federal income tax credit. However, other rebates may be available from your state, town or local electric company. To qualify for these, you may need to buy a unit with a higher SEER than the basic Energy Star standard. Depending on what rebates you can get, a higher-SEER system may actually cost less out of pocket than a lower-SEER one.
Get at least three quotes from contractors. Referrals from friends, neighbors and co-workers can be a good starting point. You can also ask local trade organizations for names of members in your area. Organizations like the Air Conditioning Contractors of America (ACCA) have directories on their websites that can be searched by ZIP code.
Ask for details. Don't trust a contractor who gives you an estimate based solely on your home's square footage. Make sure the contractor calculates your home's cooling needs according to Manual J, a tool published by the ACCA, and get a written estimate that shows all calculations, including ductwork design.
Check out the contractor's credentials. Ask to see the contractor's license and proof of insurance, and find out how long the company has been in business. ConsumerReports.org recommends looking for a company whose technicians are certified by a trade organization, such as North American Technician Excellence (NATE) or HVAC Excellence.
Expect professional behavior. Your contractor should show up on time and treat you with courtesy. A contractor who is late, unreliable or surly is not someone you'll want to have dealing with your air conditioner's problems in the future.
Check references. Get at least three references from each contractor. Call them up to ask whether they were satisfied with the work. Was it done on time and on budget? Were there any problems? You can also check with your local Better Business Bureau for complaints about the company.
Compare bids. Don't rely solely on price; you should expect to pay more for quality work. An extremely low bid is a warning sign that a contractor is likely to cut corners. The ACCA provides a handy installation checklist on their website to compare bids based on both price and quality.
Negotiate for the best deal. An estimate isn't set in stone. If you have another bid that's lower, ask the contractor to explain the discrepancy. If you ask for a relatively small discount, you will probably get it. You can also negotiate for a better warranty or service contract.
Get it in writing. Make sure to get a written contract before the work begins. Project costs, scheduling, model numbers and warranty information should all be specified. This will protect you from unwanted last-minute changes.