When replacing an existing door, measure the door’s actual width, thickness (normally 1 3/4 inches) and height (normally 6 feet, 8 inches).

If you’re buying a complete entry system and intend to replace the jamb as well as the door, measure the thickness of the existing jamb, from the inside of the exterior molding to the inside of the interior molding (this equals the wall’s thickness). Stand inside, and note which side the knob is on. If the knob is on the right, you have a “right- hand” door; if it's on the left, you have a “left-hand” door.

When buying a wood door, look for high-quality woods, durable finishes, and careful detailing. As a rule, the more intricate the carvings and moldings, and the thicker and wider the stiles and rails, the better the door. Nord’s high-end models have 1 3/8-inch panels; lesser priced doors have 9/16-inch and 3/4-inch panels.

If you’re considering an entry system, be sure all the components are from the same manufacturer; many systems are assembled by distributors, and their parts may not be designed to go together. Be sure all weatherstripping seals tightly and the threshold interlocks with the door’s bottom edge.

If the door system includes a window, look for dual, low-e glazing and be aware that, if the window is leaded, real lead (or brass) caming is more expensive than faux caming. Keep security and safety in mind. Some glass, such as Pease-Shield by Pease Industries, is highly resistant to breakage.

High-quality steel and fiberglass doors have a thermal break—an insulated separation—that prevents outside cold and heat from being conducted through the door’s skin and frame (with a fiberglass door, this break may simply be the wood frame). This is a must for cold climates; otherwise, frost may form on the door’s inside surface.

Even if it costs you a little more, a high-quality door is sure to pay you back with smooth operation, energy efficiency, low maintenance requirements, and a great look for years to come.