Reduce unwanted heat gains and you will reduce your air conditioning bills; eliminate most of the solar heat gains to which your home is subject, or its internal heat sources (coming from lighting, baths, laundry, ovens and other appliances), and you will not need much air conditioning.
That’s rather obvious, but we often forget it. The role of air conditioners – or of any other cooling system – is not so much to cool the indoor air as it is to counteract the continuous heat gains to which homes are subject.
And that makes controlling heat gains – the solar ones, and the internal – more important for energy improvements than sophisticated and highly rated cooling equipment…
Bottom line: before buying an air conditioner or installing any other mechanical cooling system you need to consider the several ways to protect your home from solar heat gains, and consider internal sources of heat...
Home Heat Gains Control
Assess the importance of the different sources of heat in your home - and act on them accordingly...
Shade your home as much as possible (using trees and shading devices);
Close your windows and doors during the hotter parts of the day;
Consider high performance windows;
Use window films in low-efficient windows.
Insulate your attic, walls and floors;
Air seal your house to avoid air infiltration;
Act on internal sources of heat;
Protect your roof.
Internal sources of heat
Do not undervalue the impact of internal sources of heat on your cooling needs. Their importance varies from home to home and with the climate, but they rank as the third leading cause of heat gains, after heat gains through windows and through the roof-attic.
Adapt your lifestyle (food preparation, baths, laundry...) in order to minimize their impact. Also consider changing from incandescent lamps to LEDs. They produce a lot less heat.
Preventing solar heat gains through windows
Windows are, typically, the most important source of unwanted heat. Close your windows during the day and shade them with awnings, shutters and other devices. And consider also tree-shade as a long-term goal, for energy savings…
Window films are another great choice to minimize solar heat gains. If your windows are old, and you are planning to remodel your home, install windows with energy-efficient frames and the right SHGC (Solar Heat Gains Coefficient) glazing. You will be rewarded with huge energy savings.
Preventing solar heat gains through the roof and the attic
The roof and attic typically rank as the first or the second leading sources of unwanted heat gains, in stand-alone homes.
Attic fans are sometimes used to prevent attic overheating and the transmission of heat to the rooms below; but they aren't a good choice (see: Attic Fans).
High levels of attic insulation are the best method to prevent heat gains through the ceiling.
Reflective barriers - aluminum foil-faced paper, etc. - can also help reduce attic temperatures, in hot climates. They are stapled to the roof rafters, on the underside of the roof. See image at left, from the EERE.
If you are going to re-roof your home, consider roofing with special cooling coatings; they will not cost you much more, and will keep your roof and home much cooler.
Preventing solar heat gains through walls
Walls aren't as important as the attic and roof when it comes to heat gains. But their role should not be minimized, and they should be properly insulated.
See: Walls Insulation
Other sources of unwanted heat
Trees, vines and other vegetation, or outside devices (pergolas, awnings…) or structures (overhangs...) can reduce outside temperatures significantly, and indirectly the indoor temperatures.