When air leaks around windows, energy is wasted. Energy is also transferred through the centers, edges, and frames of windows. Eliminating or reducing these paths of heat flow can greatly improve the energy efficiency of windows and, ultimately, of homes. Before applying new caulk, old caulk or paint residue remaining around a window should be removed using a putty knife, stiff brush, or special solvent. After old caulk is removed, new caulk can then be applied to all joints in the window frame and the joint between the frame and the wall.
Low humidity is important during application to prevent cracks from swelling with moisture.
Warm temperatures are also necessary so the caulk will set properly and adhere to the surface. Weatherstripping is a narrow piece of metal, vinyl, rubber, felt, or foam that seals the contact area between the fixed and movable sections of a window joint. It should be applied between the sash and the frame, but should not interfere with the operation of the window. The type and quality of the window frame usually affect a window's air infiltration and heat loss characteristics. When properly installed, fixed-pane windows are airtight and inexpensive and can be custom designed for a wide variety of applications.