Do you have a central air conditioner (AC) in your home that is at least 15 years old that still works but is not very efficient? Replacing an inefficient air conditioner with a more efficient model could reduce your electric bill. A new AC unit is 20 to 40 percent more efficient than one from the 1990s—and ENERGY STAR®-certified systems are even more efficient.

How much money you save by replacing your current AC unit depends on how often your AC runs and your electric rate. The best way to determine possible savings is to have an in-home assessment conducted by a qualified heating, ventilating and air conditioning (HVAC) professional or a certified energy auditor. Electric co-ops are often interested in reducing peak summer loads and sometimes offer information, rebates or a list of qualified professionals. 

Your contractor needs to size the system to your home. A unit that is too small will not cool your home to the levels you want. If it is too large, it may not dehumidify your home sufficiently, and it will cycle on and off more frequently, which can increase wear and tear on the system and shorten its life significantly. To size the system, the contractor will look at the efficiency of the home by checking insulation levels. If you add insulation where it’s most needed, you may be able to install a smaller AC unit and enjoy greater comfort and lower cooling costs. The contractor should also assess your ductwork, which is often poorly designed, leaky or inadequately insulated.

It’s good to know there are several air conditioning options suited to different situations. It may or may not be practical to change to a different type of system.

Central air conditioning is one of two types: either split or packaged. A split system, which has the cold coils inside the home and an outside unit exhausting heat, is the most common. Packaged systems, which are sometimes installed because of space constraints, combine these functions into one box located outside the home.

A heat pump can provide cooling and heating in homes with or without ducts. If you are currently using propane or natural gas as your fuel source, this may be a good option.

A ductless mini-split heat pump can be an efficient way to cool up to four zones inside the home. If your existing ductwork is in bad shape or poorly designed, this could be a good solution.

Window units are much less efficient than other options, but they can still be effective for cooling a single room. It’s worth paying a little more for a new ENERGY STAR-compliant unit, rather than the dusty $80 unit from the yard sale.

Evaporative (or “swamp”) coolers are an alternative in very dry climates. While they use a quarter of the energy and are less expensive to install than central air conditioning, they also require more frequent maintenance


  1. My husband and I are looking to have a more energy efficient AC unit installed in our home. We want to make sure that we choose the right size for our home. As you said, a unit that is too small will not cool your home to the levels we want, and too large may not dehumidify our home. We will be sure to find the right contractor to help us decide on the right size.

  2. It really is important to have an HVAC contractor come out and size the HVAC system for your home. After all, as the article points out, a ton of problems can arise if an air conditioning system is too big or too small for your home. While these problems might not seem like much at first, they can very quickly start to effect things like your energy bill and cause them to skyrocket.

  3. I like how you say that you would want to find an AC service that will size your system to your home. It would make sense because, as you say, one that is too small won’t cool enough and one that is too big will cost too much energy. My husband and I want to upgrade from a window AC to a central AC system, so we’ll have to find one that is the right size for our home.

  4. Excellent advice. Picking the right air conditioner can be a tough choice. However, knowing your needs and what options you have are crucial. Thanks for sharing!

  5. Our current AC unit is quite old and has been making strange noises. We are thinking it is time to get a new one installed. Like you said, we will need a contractor to help us size the system to our home. We’ll make sure to get this done soon!

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