One of the great paradoxes of climate change is that the very technology we've designed to keep us comfortable in the heat is also a big contributor to global warming. According to the EPA, about one-seventh of US electricity generation is used to air condition buildings, accounting for more than 4% of national greenhouse gas emissions. Making the most of that air conditioning -- or finding more efficient ways to stay cool-- could reduce overall emissions a percent or two and substantially lower your energy costs.

Top tips for staying cool

  1. To the extent you can, prevent the need for an air conditioner in the first place by closing the shades or using an awning to keep the direct sun out, using a ceiling fan or house fan, insulating the house, and planting trees to shade areas of the house that get particularly hot.
  2. Use an efficient room air conditioner (e.g. ENERGY STAR) if there is just one room that needs to be cooler. Make sure to size it properly by knowing your room dimensions when you go shopping and tell your retailer that you already help cool the room through natural means.
  3. If you need central air conditioning, get help from a professional to locate the most efficient place to install the outdoor unit. Ask a professional whether a zoned system is suitable for your home.
  4. Always buy at least ENERGY STAR rated appliances.
  5. The recommended summer thermostat setting is 78°F. Depending on where you live, you could save 5% for every degree you turn up your thermostat. If you have a programmable system, make sure the unit only runs when you need it and you aren't paying to simply cool the couch when you aren't home.

Naturally Cool
Ventilation, natural or driven by ceiling and house fans, is the most energy-efficient way to cool your house. In hot, sticky climates, ventilation causes humidity problems, but otherwise it can be used either alone or can allow you to raise the air conditioner thermostat a few degrees.

Why is your house warm? Are there certain windows that get the most sun? Shades, blinds, or an outdoor awning can prevent the heat buildup in the first place. When replacing windows consider double-glazing and low-E coatings. Incandescent lights create more heat than CFLs. Does your roof hold heat? Insulation and reflective roofing materials can reduce this dramatically.

Trees in the right place can save up to 25% of a typical household's energy used for cooling by providing shade, putting about $100 back in your pocket each year. Tree-shaded neighborhoods are also cooler than treeless areas on summer days. How your landscape can best contribute depends on your climate, so check with a landscaper or your local agricultural extension office for suggestions.

Consider your whole house: A full suite of landscape solutions, ventilation, and heat reduction strategies, combined with energy-efficient windows and doors could eliminate or reduce the need for air conditioning altogether. Even if you still use AC, if you take other natural cooling steps as well, your cooling costs will be lower -- and your heating bills too.

Chilling
If you can't avoid a cooling system, what are your options? For more moderate climates a heat pump may make the most sense. Heat pumps move warm air from your cool house to the outside. In drier climates, another option is evaporative cooling, which uses much less energy than AC. Evaporating coolers use simple evaporation of water to cool the air but it works best in low humidity.

Do you have only one room that gets too hot to inhabit? A room AC makes the most sense here.

  • Make sure you size it properly; too large and it will finish cooling the air before it finishes dehumidifying, leaving you with a cool but clammy room. You'll need to know the square footage of the room (multiply the length by the width).
  • If you have more than one window in the room, install it in the window on the shady side of the house; a window unit in direct sun uses as much as 10% more energy. And keep lights and anything else that generates heat away from the thermostat. A ceiling fan will allow you to keep the thermostat higher and ultimately use less energy.

For more than a couple of rooms, central air is the most efficient and cost effective.

  • Get smart, technical advice from someone who knows efficiency. There are many electrical contractors who are expert in energy efficiency, but many who aren't. Make sure you're working with someone who appreciates, like you, the importance of efficiency ratings, not oversizing systems, and investing in equipment not simply based on its purchase price. If your contractor looks at you quizzically when you ask what the SEER is or doesn't offer to show you the Manual J calculations (see the jargon help below), you might want to find someone else to assist you. Contractors who manage to give you a bid without doing much measurement aren't doing their job. For more tips, click here.
  • Having a well-insulated house with properly insulated and sealed ducts improves the effectiveness of the air conditioning.
  • Make sure that you get the right sized unit for both maximum efficiency and comfort.
  • If you're planning your own AC installation, try to put the outdoor unit (condenser and compressor) in the shade on the north or east side of the house. The easiest way to find the north or east side is to find your street and house on an online satellite map. Check to make sure that north is at the top of the map. Now look at the orientation of your house - the north and east sides will be at the top and right side of the home. If you can't find your home on a satellite map, find your street on a paper map, walk out to the curb and look at how the home is oriented with respect to the street and to the top of the map.
  • The outdoor unit needs lots of air flow, so avoid putting it near shrubbery that restricts the flow. Of course, check with a professional if you have any questions about the suitability of a compressor location.
  • Whether you use room or central air, replace any unit 10 years or older with an ENERGY STAR unit, which are typically 8% above the standard efficiency. The energy savings will pay for upgrade, even if you choose the highest seasonal efficiency rating (SEER) available.

Wondering about the air conditioning jargon?

  • Btu - short for British Thermal Unit. For ACs, the unit will indicate Btu/hour and indicates the amount of heat that can be removed from the room in an hour. Higher Btu rating means a bigger and more expensive AC.
  • Tonnage - another metric for determining how much heat will be removed from a space by the AC. One ton of cooling actually refers to the amount of heat needed to melt a ton of ice! It's equal to 12,000 Btu/hr.
  • SEER - short for Seasonal Energy Efficiency Ratio. The higher the SEER, the more efficient the unit is. If it's really hot and you use your AC a lot, go for a higher one because you'll save money on your electricity bills. The new national efficiency requirement for SEER is 13 but your old one might only be 6 or 7.
  • Manual J - procedures for estimating cooling requirements for homes written by the Air Conditioning Contractors of America.