Energy saving window AC units
Energy saving window AC units will cost you far less to operate than the $200 special you pick up at your building center at the start of the summer cooling season.
Don't be tricked by super-low prices into buying a cheap window air conditoiner - it'll cost you far more in combined up-front and energy costs, than if you buy the most energy saving window unit you can find. And make sure you buy the right-sized unit; an efficient window air conditioner can become very inefficient if its capacity is much bigger or smaller than the space you cool with it.
How you install a window AC unit will have a big impact on its efficiency, and how you use it will too. And of course, don't forget to dispose of your old air conditioner legally and safely. All this is covered in detail below.
Disposing of your old window AC unit
Don't just throw your old window AC unit in the trash. Don't give or sell it to a scrap dealer. Why? First, you may be breaking the law. Second, you may be helping destroy the ozone layer.
You may have heard of CFCs (chlorofluorocarbons), chemicals that are harmless at ground level but that are largely responsible for destroying the ozone layer high over our heads. These chemicals were used for much of the twentieth century as the refrigerant liquid in both refrigerators and air conditioners. CFCs are being completely phased out for both uses by 2010, and their manufacture in the US was halted in 1995, but remember that most older models still contain them, as may some units still on sale today. It is critical that you dispose of your old air conditioner through an agency or company authorized to reprocess the CFCs so that they don't escape into the environment. Contact a local refrigeration service center, HVAC dealer, or your city government or state/provincial environment department for information on safe disposal.
An old, inefficient window AC unit
Wait - is that a Bible!?
Photo by Jason Eppink, via FLICKR
For new window AC units, if you are concerned about ozone protection (and everyone should be - the ozone layer provides vital protection to all of us from harmful ultraviolet radiation from space), insist on the new R-410a refrigerant, which is much less harmful to the ozone layer (though still not entirely benign). Most manufacturers have already switched over but there may be a few laggards.
Also note that while the new HCFC compounds have a much less damaging effect on the ozone layer than CFCs, they still cause some damage, so you should still ensure your unit is safely disposed of.
If you want to upgrade to a more energy efficient window AC unit, you certainly shouldn't give or sell your old clunker to a friend or a used appliance dealer or a junk store. You'll just be passing on your problem of an energy wasting window AC unit (and high operating costs) to someone else, which might save you money but it won't reduce the negative environmental impacts of the unit. An old, energy inefficient window AC unit should be safely scrapped rather than kept in operation by someone else.
Buy the right-sized window AC unit
Don't buy too big a unit. You might see two efficient window AC units for sale, one with a higher cubic foot rating than the other, both with the same energy efficiency rating (EER). You might think the larger window AC unit will do a better job. But if it's too big for your room, it will be less efficient than the smaller one. It will likely cycle on and off frequently, which will annoy the room occupants (especially those trying to sleep!). This rapid cycling is what leads to the unit operating less efficiently, and also leads to the compressor and fan controls wearing out faster.
An undersized air conditioner will be running a high percentage of the time, which shortens its operating life, and it may overdry the room.
You need to figure out the surface area of the room and buy an air conditioner whose BTU (British Thermal Unit) capacity matches the room size. To figure out the surface area, for a simple rectangular room, multiply the width in feet or meters by the length in the same measurement unit. That gives you square feet or square meters. For more complex shapes, break the room into a combination of rectangles and right-angled triangles, and measure the length and width of each. For rectangles, multiply width by length. For right-angled triangles, multiply width by length and divide by two.
Don't try to overestimate size and think you're being conservative - again, you'll wind up with too big a unit and you won't get optimum efficiency. Once you know the surface area of the room being cooled, use this chart to select the right capacity - and adjust as indicated below. Note that room air conditioners typically come in sizes from 5,000 to 14,000 BTU per hour.
| Square feet | Square meters | |||
| From | To | BTU | From | To |
| 100 | 150 | 5000 | 9 | 14 |
| 150 | 250 | 6000 | 14 | 23 |
| 250 | 300 | 7000 | 23 | 28 |
| 300 | 350 | 8000 | 28 | 33 |
| 350 | 400 | 9000 | 33 | 37 |
| 400 | 450 | 10000 | 37 | 42 |
| 450 | 550 | 12000 | 42 | 51 |
| 550 | 700 | 14000 | 51 | 65 |
| 700 | 1000 | 18000 | 65 | 93 |
| 1000 | 1200 | 21000 | 93 | 116 |
| 1200 | 1400 | 23000 | 116 | 130 |
| 1400 | 1500 | 24000 | 130 | 139 |
| 1500 | 2000 | 30000 | 139 | 186 |
| 2000 | 2500 | 34000 | 186 | 232 |
These estimates assume two people regularly occupy the room. Increase the capacity by 600 BTUs for each additional occupant over the first two. Also add 4,000 BTUs if the unit is in a kitchen, as a kitchen produces considerably more heat. Finally, go to the next highest BTU level in the chart above, if your room has high ceilings (over 8 feet), has heavy exposure to the sun through windows facing south or west (in the northern hemisphere), or where the ceiling borders a hot attic, particularly if the attic is poorly insulated or vented.
Of course, if you are actively trying to reduce your cooling costs, for example by following my Summer energy saving tips, you may want to adjust the BTU requirement downward one category. For example, if you've thoroughly insulated your house, ventilated your attic, are going to keep window coverings shut during the day to prevent passive solar heating, have changed most or all of your heat-producing lighting such as incandescent and halogen lights to compact fluorescents or LEDs, and are willing to live with a slightly warmer, but still air conditioned home in exchange for greater energy savings, you will wind up with a system whose capacity is too high if you just use the BTU table above.
Once you've selected the BTU level you need, shop for the unit close to that BTU setting that has the best energy efficiency score. The EER (Energy Efficiency Rating) or SEER (Seasonal Energy Efficiency Rating) number from the US Department of Energy provides a good indication of efficiency. Buy the highest EER or SEER you can find. To convert between SEER and EER, see my conversion formulas at Air conditioner ratings.
Remember to check the amperage of the unit you plan to buy, and ensure it will not blow the electrical circuit where you plan to plug the unit in. For units of 7.5 amps or less, they can be plugged into any 15- or 20-amp circuit. Higher-current units will need their own dedicated circuit. (Central AC units require a dedicated 230 volt circuit).
Also look for a filter that slides out easily for cleaning, as an energy saving air conditioner can soon become very inefficient if the filter clogs up with dust. Other useful features are a unit that can thrust the air further into the room (if cooling a long, narrow room), a digital temperature readout, and a built-in timer. Take a look at the controls for the unit and make sure they are simple to use. An energy saving air conditioner whose controls are incomprehensible could lead you to overcooling the room, which could eat up any savings you might have obtained from buying the unit.
Install the unit in a shade-facing window
The more sunlight strikes the outside of your window air conditioner, the hotter the sun will make it. Since the job of the outside of the air conditioner is to get rid of excess heat extracted from the room, the unit will have to work harder to get rid of this heat if heat from sunlight is thrown in on top. So where you have a choice, put the unit in a shade-facing window, or a north- or east-facing window (assuming you're north of the equator).
South-facing windows are the worst as the hottest sun of the day comes from the south; west-facing exposure is worse than east-facing because the setting sun in the west throws more heat (and at a hotter time of day) than the east-facing sun of dawn. (If you're south of the equator, the sun still rises in the east but will probably be north of you not south, so reverse the north/south guidance and keep the east/west guidance!)
If there are trees or other buildings shading one window all day, choose that window - as long as the shading objects aren't so close to the unit that they impede air exchange. A neighbor's wall two feet from your window is not a good place to be blowing hot air onto.
When you install a window AC unit (or a through-the-wall AC unit), make sure the unit is perfectly level so that condensate drains out of it properly. Never install a unit sideways. And seal the unit into its window frame or opening so that there are no air leaks around it, as these will allow cool air to escape or hot air to enter.
Don't use your window AC unit's outside air setting all the time
Your window AC unit will operate more efficiently if, for the most part, you keep cooling down air inside the room (at least, during times when the room air is cooler than the outside air). If you have a window AC unit with an outside air option, at the very least don't use it all the time, as you'll be exchanging cool air in the room for hot air from outside. Although the hot air may become cooler than the inside air as it passes into the room, it takes energy to extract the heat from that hot air to make it cooler, and you've just blown out the nice cool air that was already inside. So use the outside air setting only to provide a bit of fresh air every so often; for the most part you should be cooling the air inside, rather than (A) expelling the cool indoor air, which you've already burned energy to cool, and (B) drawing in hot outside air, and using energy to cool that.
Use the low fan setting when dealing with high humidity
When the room being cooled is very humid, use the low setting on your window AC unit's fan. This will do a better job of drawing humidity out of the room than the high setting. Although it may not cool the temperature of the room down as fast or as far, it will result in better comfort, as a humid room at 78F will feel warmer than a dry room at 83F.
Check the window unit's seal each year
At the start of each cooling season, check your window AC unit to ensure that the seal between the unit and the window is still airtight. Moisture from indoor air in the winter, or from rainfall on the outside of the unit, can warm window frames or cause corrosion in the metal frame of the unit, both of which can damage the seal. A window air conditioner with a poor seal will reduce the efficiency of the unit and allow hot, humid outdoor air to enter the room (and the cool air you are paying to keep cool to escape).
Cover the outdoor portion of your window unit in winter
Once the air conditioning season is over you should cover the outdoor part of your window AC unit, or remove the unit and store it indoors. This will reduce corrosion of or dust build-up in the exterior fins. In cold weather you will probably save more on your heating costs by removing the unit. Metal-framed air conditioning units in particular will conduct heat from inside your room to the outside, which not only makes the room colder but will cause condensation on the inside of the frame.
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