While most home-maintenance projects will save you money over time, few will produce an immediate effect of measurable return. Maintaining your home's 'energy envelope' is one. Floors, walls, ceilings, and exterior doors and windows make up the energy envelope of your home. Properly maintained, this envelope will increase your comfort level. You can exert a finite amount of control over heat and cold with insulation in the walls, ceilings, and floors. You can seal air leaks and make all exterior walls more air-tight. Sealing gaps at doors and windows is an annual must-do. Weather-stripping comes in vinyl, rubber, foam, metal and wood. You don't need a lot of tools to install it, either. A screwdriver, razor knife, and perhaps a hacksaw complete the list of required tools. Depending on your needs and financial limitations, you can choose from a number of weather-stripping configurations. There's metal V-strip, vinyl V-strip, integral vinyl V-strip, and adhesive-backed foam (for little used doors and windows) and hollow rubber beading on a metal flange. A professional should install interlocking metal. Metal V-strip weather-stripping is durable and easy to install. It comes with a pressure-sensitive adhesive backing that allows you to install it with no tools. The V-strip is mounted on the doorframe and comes into contact with the face of the door when the door is closed. The V-strip is then flattened when the door is closed. The built-in spring tension that creates the V-shape closes the gap between the door and the frame so that air can't pass through. V-stripping is available in vinyl which performs as good as the metal type. Vinyl V-stripping is available in a type that is built directly into the doorframe. It snaps into a groove in the doorframe and you press to lock it into place. There is no adhesive. Adhesive-backed foam is installed in the same way and in the same location as the V-style weather-stripping. This type of weather-stripping is inexpensive, but it's not very durable. Installed on a busy door, it won't last three months. For frequently used doors, stick with the metal and vinyl styles. The best weather-stripping is the interlocking-metal type. It's also the most expensive. Small metal flashings are attached to the door and frame. When the door is closed, the metal flashings interlock. Used primarily at doors and on casement windows, installation requires notching the surface with a router. The special tools and tedious process often require a professional. This type of weather-stripping is installed around the entire perimeter of the door and a special threshold is installed that interlocks with the metal flashing across the bottom. With all other types of weather-stripping, a door shoe is installed at the bottom of the door. The shoe is adjusted to close snugly against the threshold. Sometimes the rubber weather-stripping is mounted on the door shoe and other times directly on the threshold. When the rubber is mounted on the bottom of the door, it wears better than when it's mounted on the threshold. Regardless of the kind of weather-stripping you select, you should check every opening to see if a problem exists. A lot of air passes through walls and ceilings, as well as the floor. There are several methods you can use around light switches, drain pipes, electrical outlets, water pipes, registers, thermostats, light fixtures, smoke detectors, floor outlets, door bell chimes, and all your doors and windows. The first method is called the candle or incense method. All you do is hold a lit candle, or burning stick of incense, next to the suspected point of the air leak. If there's a leak, the flame will flicker, or the thin stream of smoke from the incense will waiver. You can also use the 'wet finger' method. When air passes over water, it causes it to evaporate. If your fingers are wet, they'll get colder as the flow of air passes over them. The flashlight method is a bit more com