There are many types of doors available for use in your home. The best ones to use are insulated doors (IDs). IDs should be used for all residential exterior doors, including doors that lead to attics or other unconditioned areas. IDs are available in steel or fiberglass skins. Steel insulated doors are generally less expensive than fiberglass doors, but fiberglass doors offer a stainable skin, unlike the steel doors.

IDs have been shown to be superior in thermal protection, both from a heat transmission standpoint and an air-infiltration standpoint. Because the manufacturing process may differ, it is important that you understand what makes one ID perform better than another.

Recommended Features:

Urethane/Polyurethane Foam Filled
We recommend using the highest R-value foam available for insulated door construction. The door must be completely filled with the foam and not partially foam filled. Some doors use paper/cardboard honeycombing as partial filler, which can reduce the door's thermal efficiency. Other doors use expanded bead polystyrene foam, other lower R-value foams or no foams. This can also reduce the door's thermal efficiency.

Door Thermal Break
We recommend using IDs that have a wide, effective, complete thermal break between the inside and outside steel face panels. This is normally accomplished with a wood stile that completely surrounds the perimeter of the door between the two face panels. If metal touches metal, no thermal break exists, so conductive heat loss and gain can occur. If the thermal break is not a wide break, some conductive/convective losses can still occur through thermal bridging between two closely spaced, metal face panels.

Sill/Threshold with Thermal Break
We recommend using IDs that have a thermal break in the sill/threshold if the door has a sill/threshold that is made of aluminum or any other metal, and if the sill/threshold continues to the inside of the home. This is normally accomplished with a durable rigid plastic or vinyl strip that is installed in the sill/threshold directly under the bottom of the door. Some IDs use wood or polycarbonate sill/thresholds, which would eliminate the need for an additional sill/threshold thermal break.

Advanced Weather Stripping
The old "set recommendation" was to ALWAYS use magnetic weather stripping on ALL steel IDs, which is still a good idea because the magnetic weather stripping offers a very tight refrigerator-like air seal. But some of the new, large, bulbous, rubber-type compression weather stripping found on some steel and fiberglass IDs also offer a very tight seal when the door is installed level and square. The magnetic weather stripping on steel IDs can stretch out, grab and hold the weather stripping to the door, allowing more flexibility when a door is not installed perfectly square. Whichever weather stripping is used, care should be taken not to allow paint to get on the weather stripping.

Proper Installation of Weather Stripping
For weather stripping to perform correctly, the door must be installed properly. The door must be installed square and level, or even the best weather-stripping system will not work properly.