Step one, if you have siding use a insulated vinyl siding with silica gel. Replace your windows with a double or triple insulated window system. And third your doors are very important. When you do replacement anything you want the doors and windows to fit the space perfectly. We can do these things and more at Jarrett Industries.

The answer to this question is directly related to the climate that you live in.  The major window manufacturers offer glazing that is designed for the solar heat gain and temperatures in the various climate zones. You can obtain information either through a reputable window company in your area or by visting the websites of national window companies such as Anderson, Pella, Milguard, etc.

The energy efficiency of a home relies on several factors. 

The most dominant of these factors is the insulation used, both within the perimeter walls and attic.  This would include the houses ability to breath as well as maintain a good barrier.  It's not so much the amount of insulation as the type and installation methods.

Another factor that effects the energy efficiency of your home is your windows and doors.  They come in all varieties of energy ratings, and are also reliant on the installation methods used.

The third thing that I would look at is the ventilation of your attic.  If your attic has the necessary ventilation needed it can reduce energy cost as well as prolong the life of your roof system.

I say insulation should be at the top of your list. I would also take a look at your water pumps.

Here's a few of the items we actuallyp ersonally suggest when going green: http://xtremegreenhomes.com/green_options.php.

Oftentimes the attic is the place to start.  Make sure you have plenty of ventilation, both intake and exhaust.  Check the soffit cavity to make sure you it isn't clogged with insulation.  There are formulas for Square foot of attic in relation to ventilation.  If you have a vapor barrier in the ceilling a ration of 1:300 sf is ok, otherwise about 1:150 is the rule. Second, check the insulation.  All air escaping into the attic should be sealed using spray foam or other sealants. Next, depending on your geographic location, make sure you have plenty of insulation in the attic.  Finally, something as simple as installing blinds over windows can be an economical solution to saving on energy costs.  As recommended in some of the other answers, an energy audit or getting advice from any number of qualified professionals that are willing to visit your home is the best place to start.

Great insulation plays a key factor in energy savings. There are many different options available to increase the energy efficiency of your home.  James Hardie Siding is specifically designed for the climate in which it is installed. Whether you live in a climate with freezing temperatures, snow & ice or a climate with high humidity, heat, and rain; James Hardie has a siding product built for your homes specific needs. Technology has changed tremendously over the years so homes built 15- 20 years ago may have been installed with what was considered cutting edge at the time. Window replacement and the new technology that windows have now can save a great deal of energy costs. A good product that we can recommend also would be the Mezzo Vinyl Window or Integrity by Marvin Windows. These are high performance windows that are engineered to provide outstanding energy efficiency. Major appliances such as heating and A/C units can also offer great energy savings. 

For both an existing and new construction home, the top three items that provide the greatest value and return on investment are as follows:

1. Installation of LED light bulbs and fixtures in replacment of incadenscent or compact flourescent bulbs/fixtures.
2. Sealing of exterior shell of house and all top plate penetrations in conjunction with blower door test.
3. Properly installed insulation in walls and ceilings and upgrading R-Value above code requirements.

Additional items to consider include:

1. Testing and sealing of hvac system duct work
2. Upgrade hvac system condenser SEER and furnace efficiency
3. Tankless water heater
4. Solor photovoltaic system

John,

Where is the home located in terms of climate region. There are some nuances when it comes to tuning glazing packages per elevation.

Keep in mind that standard Low-e glass will reduce the amount of radiant energy that enters through the window by more than 200% over clear glass right off the bat.

WoW Home Solutions

Many great answers here regarding insulation and air sealing.  If you have a pool, also look into upgrading your pump to a variable speed pump.  They run at lower RPM for filtering than they do for vacuuming.  This can be a significant saver in energy costs... and as always, GO SOLAR!

Solare Energy has been serving San Diego for 25 years and provides our customers with a free energy audit and rate analysis before designing a solar panel system for their homes.  This allows us to accurately size the system to your energy consumption needs and get you the best value for your investment.

Learn more at www.SolareEnergy.com or call 858-547-4300 for San Diego area solar installations.

Rob Shaw
Marketing Manager
Solare Energy, Inc.
San Diego, CA

1.  Add insulation in walls and roof.  2.  Air seal your home. 3.  Install Low E or better dual pane doors and windows.

John Ford, There are an abundance of energy efficiency upgrades you can do to your 2-story home. A question to your question - do you have a small or a larger budget? Small budget - 2 options: Attic Insulation or A Foil Energy Barrier, one example is Green Energy Barrier. Blown-In Attic Insulation is inexpensive and can help with an additional R-value of 18-60 in your attic. A Foil Energy Barrier - can be placed along the rafters or floor boards and is a foil used by NASA that greatly assists with energy efficiency. Larger budget - 3 solid options: Solar panels, Replacement Windows with Krypton gas, or Insulated Siding, an insulation with a system R-value of a 4.2 that contours to your siding panel. Best, Ken 

73-79 when active in home. This can go up when everyone is at work or school.

Set it where you are most comfortable as that is why you have it.  A good idea is to update the thermostat to a programmable version that will run the A/C mostly when you are home and according to your schedule as well as at the desire temperatures.  It isn't necessarily recommended to shut off the A/C on warmer days when you are not there as it will have to struggle to catch up when you turn it back on.  This would be due to the warmer air in the home and the storage of heat in the walls, ceilings, floors etc in your home.