Measure the height and width of the Therma-Tru door frame and the building's door frame opening. Compare the two measurements. The building's door frame opening should measure 1/2 inch taller and 1/2 to 3/4 inch wider than the Therma-Tru door frame's measurement. Adjust the building's door frame opening as needed.
Hold a bubble level against the building's door frame opening to see if it is plumb. If the opening does not rest plumb, adjust the opening as needed. In most cases, striking the out-of-plumb part of the door frame opening with a hammer will force the frame into alignment. If the hammer will not move the door frame opening, loosen the opening's mounting bracket and adjust the door frame opening for plumb. Reinstall the mounting bracket.
Clean the building's subfloor at the door frame opening using a floor scraper to shave the surface and a broom to remove the debris.
Run three beads of polyurethane sealant across the length subfloor under the building's door frame opening, using a caulking gun to apply the sealant. Place one bead in the center of the opening and the other two beads along each edge of the opening. If the building has a sill pan, run the three beads across the top of the sill pan. Sill pans wrap over the edge of the building's subfloor and look like a metal or vinyl flashing.
Run a 1/2- to 5/8-inch-thick bead of polyurethane sealant around the perimeter of the Therma-Tru door frame, using the caulking gun to apply the sealant. Keep the sealant centered on the door frame's brick mold, which is the flange that butts against the exterior of the building's door frame opening.
Tilt the top of the Therma-Tru door away from the building's exterior. Walk the bottom of the door into the exterior side of the door frame opening, centering the door frame in the opening. Push the top of the door against the opening. Force the door frame's brick mold against the opening.
Drill a hole through the Therma-Tru door frame's jamb near each hinge, using an electric drill equipped with an 1/8-inch drill bit. Repeat this on the door frame's latch-side jamb.
Run a 3-inch exterior-grade screw through the holes drilled in the center of the door frame's jamb, using the electric drill to tighten the screws. One screw holds the frame near the center hinge and the other screw holds the frame near the latch.
Hold the bubble level against the hinge-side of the Therma-Tru door frame and adjust the hinge-side of the frame for plumb. Slide a shim between the door frame and the building's door frame opening, placing at least one shim next to each 1/8-inch hole in the hinge side of the door jamb. If the hinge-side screw prevents the jamb from resting plumb, loosen the screw and adjust the jamb as needed.
Run a 3-inch exterior-grade screw through the remaining 1/8-inch holes in the door's hinge-side jamb, using the electric drill to tighten the screws. Tighten the middle screw, then the top and bottom screws.
Adjust the Therma-Tru door's latch-side for plumb, using the bubble level as a guide. Measure the distance between the weatherstripping and the side of the door. The weatherstripping should have an evenly spaced gap around the perimeter of the door. If not, loosen the door frame's latch-side screw and adjust that side as needed.
Slip shims between the Therma-Tru door frame's latch side and the building's door frame opening, placing the shims adjacent to the 1/8-inch holes in the door frame's jamb.
Secure the door's latch side to the building's door frame opening with 3-inch exterior-grade screws, using the electric drill to tighten them.
Loosen the screws holding the Therma-Tru door's transport clip, using the electric drill to turn the screws counterclockwise. The transport clip mounts to the door frame at the latch hole and holds the door closed during transportation and installation.
Open the door completely. Run the Therma-Tru-supplied hinge screws through the remaining hinge screw holes, using the electric drill to tighten the screws. The supplied hinge screws extend through the hinge and into the building's door frame opening.
Open and close the Therma-Tru door several times. Verify that the door does not rub against the frame. If the door rubs, loosen the latch-side screws and adjust the shims as needed. Tighten the screws.