Replacing Your AC Unit

By Kristi Brodd | November 29, 2017

Q: With hot weather around the corner, we’re thinking about having our air conditioner tuned up. It might be even be time to replace it with a new, more efficient system. It’s about 12 years old and seems to be running okay. Would it be worth it to get a new one?

A: I’m always reluctant to discard equipment that’s working fine, even to replace it with more efficient equipment. If your air conditioning system is 12-years-old, it is time to think about getting a new one. On average, they last about 12 to 15 years. Of course there are some out there that are more than 20 years old and still cranking out cool air.

What you don’t want is to be in the middle of an August heat wave—five days in a row over 95 degrees—and have your air conditioner die. Of course it will happen at the worst time, like when your family is visiting. At that point, you’ll call your AC dealer and get him to install whatever will get the cool air flowing immediately, and then you’ll pay for that for the next 12 to 15 years.

Having the system checked now and doing some homework about what you want to replace it with will pay real dividends when the time comes. Below are some of the factors you should consider and some questions should you ask.

The single most important factor is the quality of the technician doing the work. Here’s the dirty little secret of the HVAC industry: the vast majority of heating and cooling systems installed in homes in the U.S. are not installed to the manufacturer’s specifications.  What does that mean, and why should you care?

The efficiency of air conditioning systems is tested and given a SEER rating (Seasonal Energy Efficiency Rating) – the higher the rating, the more efficient the equipment. That is, the less electricity it will use to produce the same amount of cooling.  This rating assumes the equipment is installed properly, according to the manufacturer’s specifications.

Years of research conducted nationwide demonstrates that, most of the time, proper installation doesn’t happen, which means you don’t get anywhere near the efficiency you’re paying for. On average, SEER 12 equipment performs at about SEER 7.5, so you wind up paying a lot more to keep your sister comfortable when she visits in August.

What are the biggest problems?

The first is leaky ducts. Whether you are replacing your equipment now or not, making sure the ducts are totally sealed—with duct mastic, not tape—is one of the most cost-effective things you can do, especially if you have ductwork in the attic. Attaching a high-efficiency air conditioner to a duct system that is cooling the attic, crawlspace, and the rest of the neighborhood doesn’t make a lot of sense.

The next big issue is proper sizing of the new air conditioner. Usually, contractors simply install a system that is the same size as what you have now. Some even put in something a little larger “just to make sure.” Since the vast majority of systems are already oversize, you need to make sure your contractor does an actual load calculation to determine what your house needs.  Oversize air conditioners will be less efficient, costing you more money every month. They also won’t run enough to pull the moisture out the air, causing high humidity in the house. Sometimes, especially if you’ve done any weatherization improvements, a smaller system might make you much more comfortable and will cost much less to run.

The other big issues are having the proper amount of refrigerant in the system and setting the right air flow.  When these are off, efficiency suffers and you pay more.

There are a number of contractors in North Carolina who have the training and skill to do these things right. They usually won’t be the lowest bid, but they will save you money in the long run. If your contractor blows this stuff off—isn’t willing to show you his load calculation or talk about how he measures the air flow to each room to make sure it’s right—it might be time to find another contractor.


This article was originally featured in Carolina Country Magazine. Carolina Country is a monthly consumer magazine reaching more than 700,000 families, farms and businesses in North Carolina. Published continuously since 1946, Carolina Country is distributed by subscription to members of North Carolina’s electric cooperatives. For more information visit