Caulking is one of the best energy savers you'll find for the money.
With a couple of tubes of caulk costing about $3 each, you can seal your home against the sort of air infiltration that wastes energy dollars. The object here is to stop air infiltration before it reaches the insulation buffer.
By far, the worst cold-air offenders are mechanical openings--those that pass plumbing, ventilation and electrical lines through exterior walls.
Gas lines, phone cables, dryer vents and air-conditioner refrigeration lines are among the biggest offenders, but exterior light fixtures and receptacles are also troublesome.
In addition, joints allow cold air into the insulation space. In fact, it's not uncommon for exterior caulks to fail before the house paint does, especially on heavily painted, older surfaces.
As for which caulk to buy, choose one that is able to flex with the seasonal shifts of your home, such as a siliconized acrylic caulk.
When it comes to applying caulk, resist the temptation to smooth every joint with your finger. A smoothed 45-degree joint will produce thin edges, which will be the first to lose their grip on the caulked surface. Instead, cut the applicator tip at a 30-degree angle and let the tube form the caulk in a neat, uniformly thick bead. This type of bead will last longer and is sufficiently inconspicuous when painted.
Start your project with a careful inspection of your home's exterior. Look for existing caulk that's cracked and any obvious service openings, especially those made by utility companies.
For example, if your telephone company has recently added a line and has drilled through an exterior wall, there's a good chance the opening will be larger than the cable and it will be unsealed.
Especially troublesome will be any flat-surface fixture or vent that spans lapped or grooved siding. Light fixtures and dryer vents often leak badly in these instances. As for lap siding, it's possible to splice a plastic or wooden adapter between the fixture and lap.
When replacing cracked or separated existing caulk from siding seams, first cut away old caulk with a carpet knife. Its curved, hook-like blade, lets you slice into the joint from both directions, lifting much of the bead intact.
Scrape out any waste that remains in the area. In the case of older wooden siding, the paint that supports the caulk will lift off, too. Before caulking a new bead, it's best to paint the joint with a high-quality exterior primer, which offers better adhesion than topcoat paint.
After allowing the primed areas to dry at least a day, recaulk the seam with a flexible, exterior-grade caulk. Resist the temptation to smooth out the joint. When the caulk has set long enough for it to skin over, in roughly 30 minutes, paint the joint, caulk and all.