The exterior of your home includes the windows, doors, siding and the various tools and equipment that you use outside. Many of the choices that you can make in this area can involve substantial investments since replacements can be pricey. For these sorts of investments you should do some math to determine how long it will take for the costs of your upgrade to be repaid in energy savings.

One of the more economical changes you can make is in the area of sealing your building envelope. It has been proven that a thorough caulking and weatherstripping job can cut around 25% from the heating bill of a house and provide a much more comfortable living environment. And it's such a natural DIY job, that nearly anyone can do it well.

Where does the air leak in and out? Statistically, air leakage in a house breaks down like this:

• 25% Basement sill plate (where the wood frame meets the foundation)
• 20% Exterior electric outlets
• 13% Windows
• 13% Pipe and wire entrances
• 10% Vents
• 7% Baseboards, light fixtures, electrical outlets and attic hatches
• 6% Exterior doors
• 6% Fireplaces

Most homes built prior to 1975 have little to no insulation. Homes which were built between 1975 and 1985 have approximately half the amount of insulation required to meet today's standards. Heat loss in homes is directly linked to the levels of insulation in the ceilings, walls, windows, doors, floors and basement walls, and the rate at which warm air leaks through the home.

If the siding on your home is in disrepair or your walls have a low insulation value, new siding may be on your list. The insulating properties of a material is measured in R-Values. The R-Value is the measure of resistance to heat flow. The higher the R-Value, the more of a barrier it is to heat penetration. The total R-Value for a wall can be found by adding the R-Value of each type material used in the wall. You should be targeting an R value of 25 or more for your exterior walls.

Windows make up on average 15 to 40 percent of the wall area in a house, and have the potential to allow large heat losses. In the average house, heat losses through windows can represent 22 to 37 percent of the total heat lost. Careful window selection when building a new house or renovating an old one can make a significant difference by helping to reduce heat loss.

Energy can be lost around or through the doors in your house. Air can leak around the doors and heat can be lost through them because doors generally have insulation values less than half that of the surrounding walls. If you have old wood doors, you may want to consider some replacements or the addition of storm doors. Even if your doors are in good shape, weather-stripping can make a big difference to the air flow around your doors.

Your lighting and irrigation system may also need a bit of a tune up. For starters, why not replace those old pathway lights with some new solar lights. These lights get their energy during the day, store it away and then as night falls, they illuminate the path. If you have an irrigation system install a timer on your system and set it to water at night. You can also consider a rain meter attached so that the sprinklers don’t flow if it is already raining.