Many people think of the air conditioner as something that puts cool air into the home. What it really does is remove heat from the home. So an understanding of how heat gets in the home is key to choosing the most cost-effective ways to cut summer utility bills while staying cool and comfortable.

Top Sources of Heat Gain

The sources of heat gain in a typical newer home in summer, in order of largest to smallest sources of heat, are:

1. Inside sources (appliances, lighting, people)
2. Windows (solar heat gain)
3. Attic and ductwork
4. Infiltration of outside air
5. Walls

Although the proportions of heat gain from each source vary among houses and lifestyles, the top three offer areas of greatest opportunity to save money and stay cooler.

Most cost-effective investments for reducing summer utility bills

For a typical home, here are the top six investments you can make to reduce your summer utility bills while staying cool and comfortable. The sequence is loosely based on typical potential benefits balanced with costs but will vary from house to house.

1. Window Shading. Sun control is usually a much better investment than storm windows. An exterior shading strategy should be used for any glass that receives direct sunshine or even reflected radiant heat from pavement. Reflective interior window treatments help, but they are not nearly as effective as exterior or glass solar control.
   
   Solar screens are an inexpensive, do-it-yourself treatment that can block up to 70% of the solar heat while preserving the view. Solar films (window tint) provide a wide range of properties to fit your needs. Spectrally selective films allow more visible daylight through while blocking solar heat. Look for a solar heat gain coefficient (SHGC) around .4 (no higher than .6) and a visible light transmittance (VT) of .5 or higher. The lower the SHGC, the better; the higher the VT, the better.
   
   Landscaping is great way to shade both glass and walls as well as add value to the home. Awnings are another good option with aesthetic benefits, but they're more costly.
   
   
2. Light-colored Exterior Surfaces. When repainting, re-siding or reroofing your home, choose white or light colors. It may not make a huge difference, but color choice is a no-cost way to reflect some heat. Among roofing options, a white metal roof provides the greatest benefit. Light shingles can provide a much smaller benefit.
   
   
3. Appliance and Lighting Use and Choices. In general, each three kwh of energy saved in the home can reduce the need for cooling by an additional kwh. So you save energy and money two ways.
   
   Leaving lights, computers, TVs and even ceiling fans on adds heat needlessly. Ceiling fans are considered an energy saver by keeping you cooler at higher thermostat settings, but they end up being a net energy loser if you leave them on in unoccupied rooms. Turning everything off when not needed is free. If that’s a difficult habit to enforce, install and use timers or motion sensors.
   
   When replacing appliances, look for the EnergyStar label, a verification of high energy efficiency. Also, compare the big yellow EnergyGuide labels to reveal the hidden cost (operating cost) of different models. Investing in higher efficiency will pay off. Refrigerators and freezers are especially important, since they run (and give off heat inside your home) almost continuously.
   
   Replace your high-use incandescent light bulbs with compact fluorescent lamps (CFLs). CFLs have a higher price tag but use about 1/3 the electricity, produce 1/3 the heat and last about 10 times longer -- so you save money during the life of the lamp and stay cooler. The newer electronic types do not flicker or hum and produce a warm light.
   
   
4. Attic Improvements. If space permits, increase attic insulation to R-38. In coastal south Louisiana, and where you can’t fit R-38, it can suffice to use R-19 attic insulation with either a truss-mounted radiant barrier system or a light-colored metal or tile roof. Ridge and soffit vents provide better attic ventilation.
   
   
5. Sealed Duct System. If your home is typical, your ductwork may lose 30%-40% of the cooling you pay for! That’s because most ducts are quite leaky, and the ductwork is in the hottest place on earth (the attic). The entire duct system should be sealed with mastic and mesh (not duct tape), tested by a trained professional with specialized equipment and insulated (if in an unconditioned attic) with R-8 or better.
   
   
6. High SEER A/C. When it’s time to replace your air conditioner, invest in a Seasonal Energy Efficiency Ratio (SEER) of at least 12 (SEER 10 for room size units). Make sure it has a moisture-removing capacity (latent capacity) of at least 25%, or choose a variable-speed unit that will provide good humidity control in mild seasons (especially important if choosing a SEER 14 or higher). Insist that the unit NOT be oversized. More is not better. An oversized A/C will cool-- but not dehumidify adequately -- and will cost more to operate and will not last as long.

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