Home energy Q&A: When to replace your air conditioner

By Ken Sheinkopf

Published: August 16, 2008

Q: We drive a pretty old car and every time it needs repair work, I go through the math of figuring if I'm better off fixing it or getting a new one. Now we're hearing some funny sounds from our home's 11-year-old air conditioner, and I'm having the same thoughts about putting some money into fixing it or if I'm better off getting a new one.

How can I make the right choice?

A: You've made a good analogy here, as I see similarities between the two items. Both are major cash investments and both need some maintenance and little fix-ups during their lifetimes.

There's really no precise way to measure when it is time to stop the repairs and make a new purchase, but there are certainly some guidelines on what makes the most sense.

You've gotten a number of years out of your air conditioner already.

Sure, its projected lifespan is probably still several more years, but many factors can influence exactly how long the unit will keep operating.

I've got a home near the beach and the salt air does a real number on the outdoor compressor in as little as five or six years, while I have friends up north who are still using 20-year old air conditioners that are working just fine.

The best rule of thumb I've heard for an air-conditioner replacement is to seriously consider getting a new one when major components like the motor or the compressor finally wear out. Yes, you might have problems with some parts over the years, but repair costs are usually reasonable and will keep the unit operating for some time.

This is probably the same basic reasoning you use when you decide if you need a new car, but there's one major difference here that can't be ignored — the tremendous advances in technology in energy-using equipment like air conditioners that make today's units a much better investment. This means that spending a few thousand dollars on a new unit, while considerably more than it would cost to make repairs, can give you one where the significant energy cost savings will repay that purchase cost over its lifetime. Even the most fuel-efficient cars can't make such a statement.

Air conditioners on the market today use considerably less energy than did systems built 25 years ago, or even five or 10 years ago. Federal minimum efficiency standards have increased in recent years, assuring you that even the basic system you buy today will be significantly more energy-efficient than what was available just a few years ago.

Obviously, if you live in a part of the country where you have extended periods of hot weather, then it makes even more sense to buy a new energy-efficient air conditioner since you'll be using it more and enjoying even greater savings. But even if you only use it a few months a year, rising energy costs make the economics favor replacing an older system needing serious repairs with a new highly efficient model.

So when people ask me how they can choose the right air conditioner for their home, I always give the same answer: Buy the most efficient unit that you can afford, and make sure that it is the proper size for the home. The minimum SEER rating (the standard efficiency rating used on the equipment) might be 13, but if you are willing to pay the extra money for a 14, 16 or even higher-rated one, then you will enjoy even greater energy savings.

And if the system is too large or too small for your home, it won't cool properly, won't keep the house as comfortable as it should be, and can make your bills higher than they need to be.

With gas bills as high as they are these days, doesn't it make sense to buy an efficient car that gets high miles-per-gallon? Likewise, it makes sense to buy a home air conditioner that uses less energy to cool your home.

Q: I always look forward to the end of summer when we can open up our house and enjoy the cooling outdoor breezes. However, I'm concerned about this flow of air since I have read often about controlling outdoor air. Is it bad for us to open the windows when the weather allows?

A: Nope. It's actually one of the best things you can do to both control the indoor air quality of your home and to stay comfortable without relying on your heating or cooling system.

The confusion comes about because people don't always understand that ventilation is actually the "controlled” use of air flow into and out of a house, something quite different from air infiltration which is air flowing through holes, cracks and other openings.

From a health standpoint, just think about all the potentially harmful contaminants you have in your home right now. Check out the cleaning supplies under the kitchen cabinet, the paints and solvents in your workroom, the bags of garbage sitting in the can by the kitchen door, the various perfumes and products in your medicine cabinet, or the candles and incense you sometimes light. I won't even add in the air problems when someone smokes indoors, or the fumes from your fireplace or foods you cook, or maybe even some radon problems in the basement.

So opening up your home to ventilation means that fresh air will be coming in and diluting or even totally getting rid of stale air. While you can get mechanical ventilation systems installed that will help increase the flow of air through your home, opening windows for cross-ventilation and keeping screen doors open can all help keep air moving.

If you're constantly bothered by a runny nose or itchy eyes, your best bet may be to talk to a local contractor about a good ventilation system for your home to ensure that you keep the air clean.

This can involve replacing or installing good exhaust fans that will draw the stale air out of the home or using supply-ventilation strategies to have fresh air blown inside.

Obviously, keeping cool outdoor air coming in and flowing through the home can help increase the comfort level. Fans can be very effective in keeping the home's occupants more comfortable without relying on the heating or cooling system.

There's another point to consider here, as well. Many home problems, including mold and mildew, peeling paint, rotting window sills, and discoloring in carpets and furniture can be traced to too much moisture indoors, something that can also be improved by good ventilation. When you open up the home after the summer is over and enjoy the great fall "swing season” of fresh air, you can usually notice improvements in many of these potential problem areas thanks to the airflow.

Now none of this means that you shouldn't keep a home well-sealed, plugging gaps around pipes and wires leading to the outdoors, sealing holes and cracks in the walls, foundation, around windows and doors, etc.

This is where the problem becomes not poor ventilation, but air infiltration, the "unwanted” flow of air into and out of your home.

Rather than controlling this air, this is actually a situation where you'd rather keep that air out. For example, when warm, moist outdoor air flows inside and hits cold surfaces like your windows or ducts, you can get moisture problems.

When you're trying to stay comfortable this winter, you don't want cold outdoor air coming in, forcing you to raise the thermostat setting. Keep in mind how unwanted airflow differs greatly from the air movements that you can control and use to your advantage.

Ken Sheinkopf is a communications specialist with the American Solar Energy Society ( www.ases.org). Send your energy questions to askken@ases.org.

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