Get the facts on cooling efficiency before you buy

Energy saving air conditioners can transate into big savings on your household energy budget. With energy prices seemingly always on the rise, it makes sense for you to improve the efficiency of your current air conditioner – if you can – or to find the most efficient new air conditioner you can afford.

The good news is that there’s lots you can do to cut cooling costs whether you’re sticking with your current air conditioner or planning to buy a new high efficiency air conditioner.

Most air conditioning systems sold today are energy saving air conditioners, compared to the models sold ten or twenty years ago (at least in the US and Canada). The keys to obtaining the most cooling for the lowest energy cost are choosing the right sized model for your home, the right configuration (central, ductless minisplit, portable, or room air conditioner) and the right efficiency rating, while balancing system cost with life cycle cost.

In this article I cover general guidelines for energy saving air conditioners, such as how and when to buy, maintaining proper refrigerant levels, and how to get the most out of your energy saving air conditioner using as little energy as possible.

I encourage you to check these other air conditioner-related topics which I’ve placed in separate articles linked below:

In the US alone, home air conditioning use costs $11 billion each year, and produces roughly 100 million tons of CO2. If every American household that currently has an air conditioning system (about 65% of all households) were to upgrade to the most energy saving air conditioners available, Americans could eliminate perhaps 40 million tons of CO2 emissions per year.

And save $4 billion in energy costs.

Want your share of that $4 billion?

General efficiency questions

Is your current air conditioner efficient, or is it time to look at new energy saving air conditioners? Will cleaning boost efficiency? Are there other ways to make your AC more efficient? What about refrigerant levels? What should you look for in a new unit? All these questions are covered in this section.

Is it time to buy a new high efficiency AC?

If your unit is more than ten years old, or cycles rapidly when in use (on / off / on off), it is probably time to look at newer, energy saving air conditioners.

Efficiency standards for air conditioning systems keep going up. You can probably save more than 20% of the electricity your current unit is now using, if you upgrade to a high efficiency model.

Excess capacity is another potential problem that leads to inefficiency in older units. If your central air conditioning system is more than ten years old, there’s a good chance the installer “over-spec’d” it. Installing oversized units was once common practice, and an oversized unit is much less efficient than one slightly undersized for the area being cooled. To see if your central unit is oversized, ask an HVAC contractor to check its BTU rating for you and to do a sizing on your house to determine whether it was oversized.

See the sections on buying new energy saving air conditioners on my Efficient central air conditioning and Efficient window AC units pages.

Correct refrigerant levels help your AC run efficiently


Good quality energy saving air conditioners for movable use are shipped with the correct amount of refrigerant (known as the refrigerant charge). These units, including those for window or through-the-wall installation, as well as portable energy saving air conditioners, are preloaded with refrigerant for optimum efficiency.

Central air conditioning systems have their manufacturer-recommended refrigerant charge added by the licensed HVAC company doing the installation.

That’s where the first efficiency problem can arise with a central AC system: a poorly trained or inattentive installer may install too much or too little refrigerant.

For both central air conditioning systems and movable energy saving air conditioners, the refrigerant charge may also decrease over time due to leaks.

If your air conditioning system seems to work less well over time – or it’s working harder this summer than it was last summer and seems not to be cooling as well, the refrigerant charge may be a problem. (Or maybe it’s just hotter out!)

For a central air conditioner, you should have the unit serviced at least every two years to preserve its efficient operation. Service it more often if you use it much of the year. The service call should include a test of the refrigerant charge, and the charge level should be noted on the invoice.

Also ask the technician to verify that the refrigerant charge is correct for the unit, not just sufficient. There should not be too much refrigerant.

Keep your maintenance invoices so you can ensure the refrigerant charge stays the same. If it drops from one servicing to the next there may be a leak, which needs to be fixed by a technician before more refrigerant is added.

Keep the unit clean

For either central or room units, keep your air conditioner clean. Any exposed coils, vents, fins, filters, or other parts where heat is vented, air passes through, or where moving parts are exposed to the air should be free of dust and moisture.

Make sure any condensate from a window unit is properly drained to the out of doors, preferably away from the house so that it does not drip on your foundation and increase basement humidity problems.

For central energy saving air conditioners, make sure the coils in the heat exchanger, and the fan blade and fins in the condenser unit, are cleaned during the scheduled tune-up.

Never turn the temperature way down to speed cooling

Turning energy saving air conditioners down to a very cold setting won’t make any difference to how fast you’re cooling down the indoors. Suddenly you’ll be freezing, and you’ll be wasting energy if you forget to turn the unit back to a reasonable temperature setting.

The temperature control on energy saving air conditioners only sets the low temperature the unit will stop cooling at. It doesn’t affect how hard the unit works at any given time. If you get home and you’re boiling hot and need instant relief, don’t push the thermostat way down – go and take a shower!

Anticipate hot days and cool early

Energy saving air conditioners can cool a room down for a lower dollar cost if they start up early in the day, at least in areas where time-of-use pricing is in effect. (Time-of-use or TOU pricing: you pay a higher rate at times when electricity is in high demand, and lower rates when demand drops, for example overnight.)

TOU pricing tends to be lower early in the morning before the world wakes up. So don’t wait until it’s scorching hot outside to crank up the AC – start cooling earlier, and ease up when the electricity rates go to daytime highs.

Better yet, if it’s cool at night, open the windows first and draw in as much cool outside air as possible before turning on the air conditioning system.

Heading out? Turn your AC off early

Most people run their energy saving air conditioners whether they’re at home, or out and about town. (Some of my neighbors even leave them running when they leave for their summer vacation!). This isn’t the best way to spend your money, if you ask me. When you’re going out of the room or house being cooled for more than a half hour, shut the damn thing off!

It doesn’t take long for energy saving air conditioners to start making a room or house comfortable, and there’s no point spending money to keep the space comfortable for non-existent occupants. So if you’re planning to head out, turn the room unit off ten minutes before you leave, or the house unit off half an hour before you leave.


Is letting the house get hot inefficient?

Don’t believe anyone who tells you it’s more efficient to let the unit run all the time, rather than to let the temperature in your house rise when you’re not around.

No house is perfectly insulated; some heat always creeps in from outside when it’s cooler out than in. The bigger the gap in temperature between outdoors and in, and the more poorly insulated or sealed your house, the more heat will pass through the walls as the two temperatures strive to meet equilibrium.

Energy saving air conditioners left on on all the time result in a bigger temperature difference between in and out, and so a bigger heat exchange. Ergo … more electricity used by the AC.

The other reason for turning off the AC when you go out is that … you might forget. You know that errand you thought was only going to take ten minutes? But while you’re out, you figure, might as well pick up the dry cleaning, might as well buy bread and milk, let’s stop at the bank …

Then you spot a friend you haven’t seen in ages … suddenly two hours are gone. And your AC has been running the whole time, not really doing anyone any good.

Coming and going? Try a timer

If you don’t want to come back to a warm, clammy room or house, you can put a room air conditioner on a timer (or use its built-in timer if it has one). Set it to turn on a few minutes to half an hour before you return.

For a room or portable air conditioner, remember that if you’re using a separate automatic timer, the timer has to be able to handle the amperage of your unit. Some automatic timers are only designed to turn lights on to make your house appear occupied. Look for timers that can handle 20 amps, since most standard home electrical circuits are wired at 20 amps.

As for central energy saving air conditioners, if you’re leaving during one step of the daily cycle but returning at another part, it’s safe to raise the temperature when you leave even if the thermostat is still in the comfort cycle. Programmable thermostats always revert to the regularly programmed temperature setting when the next phase of the program kicks in.

For example, suppose you have your thermostat set to:

  • 6:30 a.m. 78F
  • 8:30 a.m. 83F
  • 4:30 p.m. 78F
  • 10:00 p.m. 83F

If you’re leaving the house early, say at 7:00 a.m., you can turn the temperature up to 83F without reprogramming the unit; the house will still start to cool down to 78F at 4:30 p.m., but you’ll save the cost of keeping it cool from 7:00 a.m. to 8:30 a.m.

Does 5 degrees for an hour and a half really make that much difference? It sure does. Especially if you pay time-of-use rates, since 7:00 to 8:30 in the morning tends to be a peak electricity price period.

Use an energy-saving temperature setting

Your rooms should be cooled to between 23-26C (73-79F). Use the highest temperature in this range you can comfortably live in.

In fact, you can slowly wean yourself off that deep freeze, and work your way up to a higher ‘comfort’ temperature setting. You’ll save a lot more if you set your cooling temperature to 26C/79F than if you use the lower end of the range. Sometimes, just running the AC to remove humidity from the indoor air can make it feel cooler, even if the indoor temperature is high.

Supplement your air conditioning system with fans


Use ceiling fans and room fans to blow your air-conditioned indoor air around, in rooms where people are present.

Fans help people stay cool – by evaporating the sweat on their skin. Table fans, floor fans, and ceiling mount fans all let you get away with raising the AC temperature a little – perhaps by 2-4F (1-2C) – and no one will even notice a decrease in comfort over a room that’s air conditioned without a fan.

(Of course, if they’re wearing a wool suit, there won’t be too much chance for sweat to evaporate from their skin, but why are they wearing a wool suit in hot weather!?)

Compared to air conditioning systems, fans use practically no energy at all. Just remember that there’s no point in running a ceiling fan, or any other fan that just blows air around inside, unless there are people there to benefit from the evaporative cooling from the fan. In fact, a fan blowing air around inside a closed room with no occupants is actually adding heat to the room, not cooling it.

Follow these summer energy saving tips

Over and above these tips specific to making energy saving air conditioners more efficient, follow my summer energy saving tips, which cover a wide range of things you can do to save energy in the summer, including tips to keep your house cool without using air conditioning as much (or at all).

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