Getting the Most Efficiency Out of Your Room Air Conditioner
Room air conditioners have become considerably more efficient, which means you can actually save money by replacing your old room air conditioner with one of the new efficient models, especially in this era of rising electricity prices. How to choose the right one?
 First, take as many of the steps on the preceding pages of this section as you can to tighten up your house and lower your need for air conditioning. You may actually find that you don't really need to have an air conditioner after all.
If you still want one, there are a number of decisions you will have to make. Central air conditioning systems are more energy efficient than room air conditioners. If getting central air makes sense for you, check out the next section. However, if you would only cool one or two rooms it would probably be cheaper to use a room unit, so read on.
If you opt for the room air conditioner, you must choose between a wall-mounted and a window mounted model. Wall-mounted units cost more to install (and you have to put a hole in your wall) but you can seal them easier than window-mounted units, so less of the nice cool air you are paying for leaks back outside. Plus, a window unit will block your view and light.
The next step is very important: get the right size unit for your needs. If you install an oversized air conditioner, it will run for shorter periods and cycle on and off more frequently. It also won't dehumidify as much so you won't feel as comfortable and will set the temperature even lower. Result: higher electricity bills.
The best way to get the right sized unit is to ask a qualified air conditioning technician or energy auditor for a thorough analysis, which will include local climate information and calculations of heat gain through your windows and walls. Be sure to tell your technician or auditor about all the steps you have taken to lower your need for air conditioning. Whatever you do, don't accept the simple rules-of-thumb used by a salesman to calculate how big a system you need. You will end up buying a bigger system than you need. You won't just pay more now for the bigger model; you will pay later in bigger electricity bills.
Once you know the size of the room air conditioner you need, look for one with the highest EER rating you can find. EER stands for "Energy efficiency ratio" or the ratio of the cooling output in British thermal units (Btus) over the power consumption. New national standards went into effect in October of 2000 which required an average EER of about 10, although the minimum efficiency varies depending on the design and cooling capacity of each unit. Your best bet is to buy an air conditioner that has an EnergyStar® label if you can find one. Remember that even though the higher energy-efficient units cost more, they will pay for the price difference in savings on your electric bill over a few years--or less, given rising electricity rates--especially if you live in hot climates.
Additional energy-saving features you will want on your air conditioner are: (i) a fan-only switch to use to ventilate your house at night for big savings over air conditioning; (ii) a filter check light which tells you when it is time to check the filter; and (iii) an automatic delay fan switch which turns off the fan a few minutes after the compressor stops.
Those of you who live in humid climates will also want a model that is effective at removing moisture and one that includes a variable-speed or multispeed blower. Running the unit on a lower speed will reduce your efficiency somewhat but will dehumidify your home more, so use the lower speed only on very humid days. You can get a model with a variable-speed blower that is controlled by a humidistat, which automatically changes fan speed according to the current humidity.
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