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updated 6/8/2010 9:36:22 AM ET 2010-06-08T13:36:22

Temperatures aren't the only numbers that climb in the summer. With air conditioners on full blast, so do energy bills.

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Cooling costs run the average homeowner about $400 a year, according to Energy Star, the government program that promotes energy efficiency. But you can control your expenses with a few simple measures.

Whether you have central air conditioning or a window unit, here's how to keep costs down.

Find the right unit
Let's start with window units. Their cooling capacity is measured in Btus, and the amount required depends on the size of the room.

You don't want a unit that's too weak, of course. But getting one that's too powerful isn't a good idea either.

That's because the room will cool too quickly and the unit will be turned on and off more frequently. This not only wastes energy, but interferes with the air conditioner's ability to regulate humidity. So the room could be left feeling damp and uncomfortable.

The recommended Btu capacities for various room sizes can be found on the Energy Star website at www.energystar.gov. Note that adjustments should be made depending on certain factors. For example, sunny rooms need more cooling power, while well-shaded rooms need less.

Units that have the Energy Star label indicate that they're more energy efficient than standard models.

The same is true for central air conditioners. However, those looking for central air units are likely working with contractors who can recommend the right cooling capacities and models for a home.

An important point to remember when letting a contractor take the reigns is that central air units usually come in multiple parts. To ensure maximum energy efficiency, make sure the parts your contractor uses are from the same manufacturer or approved to work together.

You also might want to invest in a new unit if your central air system is more than about 15 years old, because the money will likely be earned back on lower energy bills, said Maria Vargas, a spokeswoman for Energy Star.

A tax credit of up to $1,500 is also available for central air units through the end of the year. Prices for central air units and installation vary greatly, so get quotes from at least a couple places before making a commitment. Generally, it will likely cost at least $2,000.

Seal and maintain
Even if a system is energy efficient, cold air can leak out of a home that isn't properly sealed. Such leaks would also mean higher heating bills in the winter.

It's usually easy to tell if there's a draft in your home. But if you want to double check, there's a do-it-yourself home sealing guide on Energystar.gov.

To avoid air escaping around window units, be sure to carefully follow the installation instructions. And clean or change the air filter about once a month — or whenever you see significant dander buildup — so the unit doesn't have to work as hard.

Ideally, window units should also be taken out and stored during winter, said Glenn Hourahan, a spokesman for the Air Conditioning Contractors of America. This minimizes the draft that comes in through the unit and prevents dirt or leaves from getting lodged in vents. If it's too much trouble to take out and reinstall the unit every year, however, Hourahan suggests at least securing a wrap around it in cooler seasons.

Anyone with central air should check for cracks in exposed ducts. But don't just tape over cracks — use a sealant called mastic that's designed for the job.

Tweak habits
Small changes can add up to considerable savings, too. For example, it might be tempting to leave the air conditioner on while you're out so your place will be cool when you return. But the habit can run up energy bills.

Instead, buy a programmable thermostat for central air conditioners, or get window units with built-in timers.

On days when it's not too warm, try staying cool with a ceiling or room fan. Even when it's hot, keep the fan on and run the air conditioner at a lower strength. Raising the thermostat by just two degrees can save as much as $30 a year, according to Energy Star.

That doesn't mean you should leave the fan on all the time. Unlike air conditioners, fans don't cool the air — they cool people. So there's no point in keeping a fan on if you're not in the room.

Finally, don't underestimate the power of shades and curtains. Draw them closed before leaving for work, so rooms don't bake while you're out.

Copyright 2010 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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